Arsenic, Drinking-water and Health Risks Substitution in Arsenic Mitigation : a Discussion Paper World Health Organization 2003 The illustration of the cover page is extracted from Rescue Mission: Planet Earth, Peace Child International 1994; used by permission All rights reserved. This information material is intended for a restricted audience only. It may not be reviewed, abstracted, quoted, reproduced, transmitted, distributed, translated or adapted, in part or in whole, in any form or by any means. The designations employed and the presentation of the material in this health information product do not imply the expression of any opinion whatsoever on the part of the World Health Organization concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. Dotted lines on maps represent approximate border lines for which there may not yet be full agreement. The mention of specific companies or of certain manufacturers' products does not imply that they are endorsed or recommended by the World Health Organization in preference to others of a similar nature that are not mentioned. Errors and omissions excepted the names of proprietary products are distinguished by initial capital letters. The World Health Organization does not warrant that the information contained in this health information product is complete and correct and shall not be liable for any damages as a result of its use.
Transcript
Arsenic, Drinking-water and Health Risks Substitution in Arsenic Mitigation :a Discussion Paper
World Health Organization 2003
The illustration of the cover page is extracted from Rescue Mission: Planet Earth, Peace Child International 1994; used by permission
All rights reserved.This information material is intended for a restricted audience only. It may not be reviewed, abstracted,quoted, reproduced, transmitted, distributed, translated or adapted, in part or in whole, in any form orby any means.
The designations employed and the presentation of the material in this health information product donot imply the expression of any opinion whatsoever on the part of the World Health Organizationconcerning the legal status of any country, territory, city or area or of its authorities, or concerning thedelimitation of its frontiers or boundaries. Dotted lines on maps represent approximate border lines forwhich there may not yet be full agreement.
The mention of specific companies or of certain manufacturers' products does not imply that they areendorsed or recommended by the World Health Organization in preference to others of a similar naturethat are not mentioned. Errors and omissions excepted the names of proprietary products aredistinguished by initial capital letters.
The World Health Organization does not warrant that the information contained in this healthinformation product is complete and correct and shall not be liable for any damages as a result of itsuse.
WHO/SDE/WSH/03.06Distr: Restricted
English only
Arsenic, Drinking-water and Health Risk Substitution in Arsenic Mitigation:
a Discussion Paper
Author:Guy Howard, Programme Manager WEDCLoughborough University, Leicestershire, UK
A report prepared for the Arsenic Policy Support Unit,Local Government Division, Government of Bangladesh
World Health OrganizationGeneva 2003
TABLE OF CONTENTS
PageExecutive Summary ............................................................................................................... i
1.0 Introduction..................................................................................................................... 12.0 Nature of hazards that may substitute for arsenic....................................................... 1
2.1 Comparing risks from microbial hazards and arsenic ............................................ 22.2 Nature of health effects .......................................................................................... 22.3 Comparing risks from other potent ial hazards ...................................................... 4
3.0 Technology options and controlling risks ...................................................................... 43.1 General issues regarding risk substitution.............................................................. 53.2 Pond sand filters .................................................................................................... 63.3 Slow-sand filters..................................................................................................... 63.4 Dug wells................................................................................................................ 73.5 Deep hand tubewells .............................................................................................. 83.6 Rainwater harvesting ............................................................................................. 93.7 Arsenic removal technologies ............................................................................... 93.8 Household treatment of water for microbial hazards............................................. 11
4.0 Ongoing surveillance and support ................................................................................. 115.0 Summary ......................................................................................................................... 12
Appendix-1Water safety issues and examples of ‘model’ Water Safety Plans .......................................... 14
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Arsenic, Drinking-water and Health Risk Substitution
in Arsenic Mitigation: a Discussion Paper
Executive Summary
Risk substitution• There are water-related health risks
associated with all forms of water supply.In reducing one water-related health riskanother may be substituted, sometimes ofgreater magnitude. In Bangladesh, aconsequence of reducing the risk frommicrobial contamination of drinking waterwas the inadvertent substitution of a riskfrom arsenic.
• In developing an emergency response tothe arsenic crisis, the potential for risksubstitution from other hazards must beconsidered. Water supply options shouldbe selected within an overall riskmanagement framework of Water SafetyPlans. In selecting options, it is importantthat a consistent approach is adopted inevaluating all risks.
Substitute hazards• The hazards that may substitute for arsenic
include: microbial hazards (pathogens);toxins derived from cyanobacteria insurface water; and chemical contaminantsfrom pollution. This report provides aqualitative risk comparison betweenarsenic and other hazards, but quantitativerisk comparisons should be considered asa priority in the short term.
Risks and poverty• Risks from both arsenic and microbial
hazards are strongly related to poverty andnutrition, and for microbial hazards thereis a synergistic relationship betweenunder-nutrition and repeated infection bymicrobial hazards.
Nature of health effects• Microbial hazards lead to acute health
effects and attack rates commonlyrange from 20 to 70%. Effects rangefrom self-limiting diarrhoea tomortality. Mortality is more commonin particularly sensitive sub-groups(infant, children, immuno-compromised and pregnant women).
• Arsenicosis is a chronic disease with asignificant latency period for non-cancerand cancer effects. The proportion of apopulation exposed to elevated arsenicthat will develop arsenicosis is uncertain,but may be significant.
Treatment of health effects• Medical treatment of infections by
microbial hazards is generally wellunderstood. In practice access may belimited to medical care, particularlyamong the poor.
• Medical treatments for arsenicosis are notfully developed. There is indication thatswitching to arsenic-safe water and anti-oxidants may reverse symptoms in earlystages.
Comparing the risks• Overall the risks posed by microbial
hazards are greater than those posed byarsenic. This does not mean arsenicmitigation is not important but thatemergency response measures must ensurethat risks from microbial hazards do notincrease.
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• For all options considered in theemergency programme, hygiene educationwill be essential to promote safe waterhandling.
• In the short term it is unlikely that risksfrom cyanobacterial toxins will be greaterthan those posed by arsenic, but in thelonger-term would need to be consideredin defining appropriate water supplyoptions.
Audits in emergency response• During implementation of the emergency
response, third-party audit of constructionquality is essential and should apply to allagencies undertaking construction.
Effective control of risks• Although designs can include effective
control measures for microbial hazards,good operation and maintenance isessential to ongoing risk management,even within the short timeframe of anemergency response.
• Community operators require propertraining in O&M, including action-oriented monitoring and must have accessto the appropriate tools. In addition totraining of operators, O&M should besupported through development of anongoing surveillance programme.
Pond sand filters• The performance of pond sand filters is
often poor and there are concernsregarding both the ability to reduce risksfrom microbial hazards and cyanobacterialtoxins. Consideration is being given todevelop slow-sand filters as a moreeffective alternative to pond sand filters.The use of any technology for treatingsurface water must meet clear criteriaregarding selection of ponds.
Dug wells• There is some evidence emerging of
arsenic contamination of dug wells. Dugwells are also vulnerable to microbialhazards. Although these can be reducedthrough good design it is difficult to assurewater safety in the monsoon and
chlorination may be needed. It may bemore appropriate to consider renovation ofdug wells rather than construction of newwells.
Deep hand tubewells• Deep hand tubewells are an attractive
option as microbial hazards are relativelyeasy to control. More recent data indicatesthat the deep aquifer is contaminated witharsenic in some areas. This needs urgentclarification.
• The USGS study will provide furtheruseful information to base decisionsregarding the use of deep hand tubewellsoutside of areas that have been shown tobe arsenic-safe.
Rainwater• The risks posed by rainwater harvesting
are relatively easy to manage. Rainwatermay not last the whole dry season andtherefore promotion of rainwater will needto be combined with other solutions.
Arsenic removal• Arsenic removal technologies were not
included in the short-list of emergencyoptions as none had been formally verifiedthrough the ETV. The disadvantages notedfor risk substitution for arsenic removaltechnologies are shared by otheralternatives and do not appear adequate todisbar consideration in an emergencyresponse. Community-level technologieswould be more attractive than householdoptions at this stage.
Household water treatment• Household treatment of water to remove
microbial hazards could be considered asan option as there is evidence that thesehave a significant impact on diarrhoealdisease. Promotion of household treatmentfor microbial hazards could be consideredin conjunction with other emergencyinterventions.
Surveillance• A programme of water quality
surveillance should be developed tosupport the emergency response and the
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longer-term mitigation strategy. This canbuild on pilot activities in urban areasundertaken by DPHE and WHO and theprotocol for surveillance in rural areasdeveloped recently for DPHE. Thesurveillance programme should includetesting for E.coli or thermotolerantcoliforms and a rolling programme ofrepeat testing of tubewells for arsenic.
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Arsenic, Drinking-water and health risk substitution in arsenicmitigation: a discussion paper
1.0 Introduction
A key policy lesson for public healthprotection that emerges from thearsenic crisis in Bangladesh is that inimproving water supply services,consideration must be given of thedegree of public health risksubstitution that may result. In the caseof Bangladesh, the provision oftubewells tapping the shallow aquifersubstituted one public health risk(diarrhoeal disease) by another fromarsenic. This risk substitution was notpredicted at the time and the evidenceof the potential for such a substitutionwas certainly not adequate for anevaluation of the probability and natureof potential substitutes.
In developing the arsenic emergencyprogramme it is essential the potentialfor risk substitution is properlyevaluated and that the selection ofwater supply options is undertakenwithin an overall risk managementframework. Increasing scientificknowledge of the nature of differentrisks and how these may be controlled,makes such evaluation both practicaland urgent in the arsenic emergencyresponse.
This paper discusses some of the keyissues that arise in relation to potential
risk substitution from alternative watersupply options, taking into account thevarying nature of risks and thepotential for their management. Withinthis framework, the efficacy and easeof medical treatment is considered aswell as the management actions thatcan be taken to reduce exposures tohazards in drinking water. The paperdraws on the developing paradigm ofwater safety plans, the approach thatforms the basis of the revised 3rd
edition of the WHO Guidelines forDrinking-Water Quality (GDWQ).
The key tool within the revisedGDWQ is the development andimplementation of Water Safety Plans(WSPs) related to health-based targetsfor water safety. The development ofthis approach has particular relevanceto microbial hazards. WSPs arecomprehensive management plansfrom catchment to consumer that whenput in place will assure water safetyand outline the necessary means ofmonitoring and verifying that suchrisks have been managed at a leveldetermined as tolerable in the contextof overall disease burden. Documentssupporting this report containexamples of WSPs for small systems.
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2.0 Nature of hazards that may substitute for arsenic
There are three principal types ofhazard that could be expected topotentially substitute for arsenic fromwater supply provided during anemergency response. These are:
• Microbial hazards: pathogensderived from human and animalfaeces that cause diarrhoea, aswell as a range of other diseases,some with significant chronicsequelae;
• Toxins derived fromcyanobacteria that may lead toadverse health effects includingliver cancer; and,
• Chemical contaminants in sourcewater introduced from pollution.
2.1 Comparing risks from microbial hazards and arsenicMicrobial hazards represent an overallgreater threat than chemical hazardsand in developing countries accountfor a significant proportion of theburden of disease. Diseases due tomicrobial hazards from poor water,sanitation and hygiene are responsiblefor 5.7% of the total global burden ofdisease. For microbial hazards, as forcarcinogenic risk from arsenic, it isassumed that no safe threshold existsand that any exposure has the potentialto initiate an adverse health effect.
When comparing the risks associatedwith arsenic and microbial hazards,several important points emerge. Bothare strongly influenced by poverty andnutrition. Risks of infection bymicrobial hazards (pathogens)increases markedly with increasingpoverty. The overall health burdenfrom pathogens is significantly greaterin poorer communities. Arsenicosisalso appears to be related to povertyand has a greater incidence amongpoorer households exposed to elevatedconcentrations of arsenic. For bothpathogens and arsenic, poor nutrition is
likely to contribute to greatersusceptibility. In the case of microbialhazards, repeated infection alsosignificantly contributes to under-nutrition.
The degree of uncertainty regardingthe epidemiology of arsenic-relatedhealth effects and the progression ofarsenicosis makes quantitative riskcomparisons with health effects frommicrobial hazards difficult. Equally,there is significant uncertaintyregarding the role of drinking-water ininfectious disease transmission inBangladesh, primarily because of thelimited water quality data and thelimitations of data solely expressed interm of index organisms. Undertakingquantitative risk assessment iscertainly possible, but would requirecollection of further data on targetpathogens in drinking water and thisshould be considered as a priority inthe short-term. However, althoughquantitative risk comparison may bedifficult, qualitative comparisons arepossible and are outlined below.
2.2 Nature of health effectsThe nature of health effects betweenmicrobial hazards and arsenic are verydifferent. Arsenicosis is essentially a
chronic disease and there is asignificant latency period beforesymptoms are developed. There
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appears to be discrepancy in theliterature regarding latency, with somereports of 2 years being the minimumfor hyperpigmentation and keratosis.Researchers in Bangladesh suggest that5 years is the minimum latency, whilstsome other estimates suggest that thisis 9 years. Latency for cancers is alsounknown, but it is estimated to be ofthe order of 20 years.
Microbial hazards typically lead toacute health effects with (in all but afew cases) incubation periods oftypically hours to days. Most episodesof infection lead to self-limitingdiarrhoea provided fluid replacement ispractised. However, all pathogens canlead to mortality and this may besignificant in sensitive sub-populations, notably infants andchildren (all pathogens), immunecompromised (often to specificopportunistic pathogens) and pregnantwomen (specifically in relation tohepatitis E virus). Furthermore,although many episodes of diarrhoeaare in themselves self-limiting, there isa synergistic relationship with under-nutrition from repeated episodes.
The proportion of a populationexposed to elevated arsenic fromdrinking-water that will go on todevelop arsenicosis is unknown. WHOhave modelled the progression ofarsenicosis using data from Samta,Bangladesh. The range of thoseaffected over 30 years was 15.75% inthe lowest estimate scenario to 29.25%in the highest estimate scenario.Variation in the estimates of mortalityfrom cancers was between 5.0 and6.5%. This implies a significant overallhealth burden for those affected.
Estimating the number of people thatwill develop symptoms of an infectiousdisease from exposure to pathogens isalso uncertain, as this depends in part
on the dose ingested and susceptibilityof the host, but outbreak data suggestthat this is in the range of 20% to 70%.The proportion of those who becomeinfected who die varies, but is typicallylow among healthy adults with muchhigher rates for sensitive sub-populations.
Medical treatment for microbialhazards is generally well-understood,although in practice access to therequired interventions may be limited,particularly among the poor. Somesequels (e.g. reactive arthritis) may bemore problematic to treat.Treatment of arsenicosis remains anarea of uncertainty. Current evidencesuggests that during early onset,switching to arsenic safe waterreverses symptoms, although there is alack of controlled trials in Bangladeshon which to validate this and toidentify the stage at which this is nolonger effective. It is not clear whetherearly removal of arsenic-contaminatedwater would reduce the onset ofcancers, but it is assumed that it wouldhave some impact because of thecumulative nature of the risk.
More recent work suggests that anti-oxidants within vitamins A, C and Eand possibly compounds containingzinc and selenium also work to reversesymptoms. A recent controlled trialwas performed in Bangladesh, but thisremains to be published and mayrequire further controlled clinical trials.However, this does indicate thenecessity of combining bothenvironmental and medicalinterventions for arsenicosis.
The nature of the acute health effectfrom microbial hazards, the particularimpact on sensitive sub-populations,the typical attack rates and thesynergistic relationship with under-nutrition show that the risk posed by
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microbial hazards is greater than forarsenic. This does not imply thatarsenic mitigation is not important, butto emphasise the need for emergencyresponse measures to ensure that riskfrom microbial hazards do notincrease.
Experience shows that control ofmicrobial hazards in the technologiesconsidered for the emergency responseis possible, but that in order to achievethis control actions are required in theshort and long-term. The Section 3 ofthis paper will identify specific issuesthat need to be considered and suggestways in which control can bemaintained. Examples of water safetyplans for most of the technologies areprovided in the supporting documents.
It should also be recognised that iftechnologies are introduced that are notacceptable to the end users then notonly will the risk from arsenic continueto threaten the health of some of thepopulation, but risks from microbialhazard may also increase as watersupplies deteriorate. Part of theacceptability will include the typicallygreater distance to the source that willresult from most of the optionsconsidered in the emergency response.There will be a need for ongoingeducation and effective riskcommunication to prevent householdsfrom maintaining use of existingcontaminated tubewells for water fordrinking and cooking.
2.3 Comparing risks from other potential hazardsThe risks associated with toxinsderived from cyanobacteria includeliver cancer. Other effects includeacute poisoning from immersion inwater where there is a bloom.Cyanobacterial blooms are found insurface waters with high nutrient loadsand recent work in Bangladesh hasidentified that these blooms occur insome ponds in the country. Nutrientloads may be derived from generalpollution and commercial fish-farmingmay further contribute to phosphateand nitrate input. In addition to directadverse health effects, algal bloomsoften lead to significant taste andodour problems that may lead to therejection of a source by users.Although toxins from microcystis(particularly microcystin-LR) may leadto cancer end-points, the overall healthimpact of cyanobacterial toxinsremains unclear. Within the short-timehorizon of an emergency response it isunlikely to represent a greater risk thandrinking arsenic contaminated water.Furthermore, as discussed below some
removal of toxins may be possiblethrough water treatment.In the longer-term response to arsenic,however, the risks from cyanobacterialtoxins may be more significant giventhe extended duration of consumption.This will therefore need to beaddressed in defining water supplyoptions. It would seem unwise at thisstage to consider the use of a watersource that is known to be affected bycyanobacterial blooms for anyintervention likely to extend beyond avery short-time period and only then ifno other options were available andthere was strong preference forcommunities for use of pond water.Other potential hazards includechemical derived from pollution, forinstance nitrate and pesticides fromagriculture and heavy metals fromindustry and air pollution. Althoughthere is evidence of pollution ofsurface waters and from air pollutionin urban areas, the overall risksassociated with such pollution will be
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significantly lower than for microbial hazards and arsenic.
3.0 Technology options and controlling risks
A short list of technologies has beenidentified by the National Committeeof Experts (NCE) as suitable forconsideration in the emergency
response to arsenic (that is in villageswhere the proportion of arseniccontaminated tubewells exceeds 80%).These are:
• Pond-sand filters• Dug wells (also referred to as
ring wells)• Deep hand tubewells• Rainwater harvesting
It is envisaged that direct provision ofthe first three technologies by DPHEand partners in a supply-drivenapproach, but that Government wouldonly engage in promotion of rainwaterharvesting. The NCE excluded arsenicremoval technologies fromconsideration in the emergencyresponse. These are considered here,however, as the rationale for exclusionof these technologies appears to beinconsistent with approach used toaccept the other technologies.Household treatment of water toremove microbial hazards is alsobriefly considered.
3.1 General issues regarding risk substitutionIn discussing the potential for risksubstitution and risk management foremergency response technologies,some general key points emerge. Forall options used in the emergencyresponse, hygiene education will beessential to promote safe handling ofwater to reduce re-contamination andincreasing risk from microbial hazards.A WSP for water handling is includedin the supporting documents to thisreport.
The NCE raise the importance of thirdparty audit to ensure that allcomponents of the intervention(including construction quality) havebeen followed. This is essential and itis recommended that in the firstinstance this is done on a blanket ratherthan sample basis. This also requiresthat standard designs are developedwith indicative unit bills of quantitiesprepared. Standard auditing proceduresand forms should be developed and
used. Where audits identify failure tocomply, there should be a requirementfor the constructing agency to makethe required changes at their own cost.It is important that auditing is appliedto all water supplies constructed,irrespective of whether this is byGovernment, private sector or NGOs.Although designs and construction canprovide control measures for hazards,experience from around the worldshows that risk management ofmicrobial hazards in particular isdependent on good operation andmaintenance. Even within the shorttimeframe envisaged in the emergencyresponse, poor operation andmaintenance may lead to a significantincrease in risk.Ensuring good operation andmaintenance in community suppliesrequires two key interventions.Operators must be provided withadequate training and provided withthe basic tools with which to undertake
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maintenance tasks. Training shouldalso include basic skills in monitoringthe water supply through action-oriented inspection to ensure thatincipient problems are resolved. Thesecond activity should be a process ofongoing support through a surveillanceprogramme that ensures that periodicinspection and testing of the watersupply is carried out and results used tosupport communities in ensuringeffective operation. This latter point isbriefly discussed further below inSection 4.
For options that use groundwater,controlling contamination requires
both proper wellhead/sanitarycompletion and control of contaminantsources around the facility. The latterare termed protection zones and aretypically defined for both microbialand chemical contaminants. Thisincludes, for instance, exclusion of on-site sanitation close to the tubewell toprevent contamination of the aquifer.Simple methodologies are availableand have been based on work inBangladesh. Further assessments areproposed to define safe distancesbetween latrines and tubewells in thecountry through DPHE/UNICEF.
3.2 Pond sand filtersPond sand filters (PSF) were designedbased on the principles of slow-sandfiltration although actual designsviolate several these principles,including depth of filter bed, flow rateand intermittent supply (head) abovethe top of the filter. As the PSF drawwater from surface water sources, thepotential for microbial hazards to bepresent in source waters is very high.In addition to contamination by humanfaeces, the potential for animal faecalcontamination is likely to besignificant and hazards of particularconcern will include E.coli O157,Cryptosporidium parvum andCamplyobacter spp. In ponds affectedby algal blooms or receiving highnutrient loads, the risk fromcyanobacteria toxins will also beincreased.
Although some reports suggest thatPSFs are efficient in removingmicrobes, this has only addressedthermotolerant coliforms. Other resultsindicate that in practice performance iscommonly poor and that microbialcontamination of final waters iscommon. Concerns have been raisedabout the ability of pond-sand filters toremove pathogen loads in very heavilycontaminated ponds and would requirea further disinfection stage to beeffective.
Overall, the generally poorperformance of the PSFs suggests thatthese have significant potential for risksubstitution and would not be apreferred solution in most cases.
3.3 Slow-sand filtersUNICEF are considering trying tomodify the PSF design to becomeslow-sand filters, with potentially useof pre-filtration. In a variety of studies
at both bench and field slow-sandfilters, removal rates of viral andbacterial pathogens have been shownto be effective. Up to 5-log removals
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of bacterial index organisms andviruses are recorded in the literature.Interestingly, although removal ofGiardia cysts is relatively good, ingeneral the removal ofcryptosporodium is far less effective.The influence of turbidity on slow-sand filter performance is well-knownand has led to the development ofmulti-stage filtration units that provideeffective turbidity removal prior to theslow-sand filter. Roughing filtersshould be capable of removingreasonably fine material and algae.However, if the turbidity is principallyclay material, removal may not be asefficient, although with microbialcolonisation of the media this could beexpected to improve. The potential foruse of geotextiles to improve the speedof schmutzdecke formation could alsobe considered.
Slow-sand filtration is effective inremoving algal cells, which may beenhanced where there is some form ofpre-treatment to reduce algal cellloading to prevent increasingfrequency of removal of theschmutzdeke. There have beenlaboratory-based studies of toxinremoval that showed removal ofvarious toxins in the range of 30% to80%, but reporting of performance inthe field is not available.In developing a slow-sand filter,consideration should be given todevelopment of two units in parallel,
which would be usual recommendedpractice. Although there are clearlygood financial reasons for use of asingle unit, this will lead to asignificant increase in risks ofmicrobial breakthrough during theripening period. Although this riskcould be mitigated by applying a finaldisinfection stage, this may not providefull protection (for instance ifbreakthrough also includes particles)and would increase both cost andoperation requirements. In ponds withalgal blooms, the filter ripening periodwould almost certainly increase therisk of toxin breakthrough, althoughthis would not be likely to be at levelsthat are acutely toxic.
If slow-sand filters are to be used, clearcriteria will be required to determinewhich ponds are suitable for use, forinstance clearly defined set-backdistances for animal rearing. Thedevelopment of a standardised format(similar to those available in the WHOGuidelines for Drinking-Water QualityVolume 3) is an important tool indetermining whether PSF is a viableand appropriate option. Such a toollogically needs to include measures forassessing risks of cyanobacteriapresence. Simple tools are available forsuch assessments using visualinspection and, where available,assessment of total phosphorous as alimiting nutrient for biomassdevelopment.
3.4 Dug wellsHand-dug wells of various descriptionsare a familiar technology inBangladesh and several standardiseddesigns are available approved byDPHE for use. However, there isevidence emerging that some dug wellsare contaminated with arsenic abovethe Bangladeshi standard of 50µg/l.
This makes their use more problematicas investment in dug wells may notresult in any reduced risk from arsenic,but an increased risk from microbialhazards - thus a double risksubstitution.
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The vulnerability of dug well tomicrobial contamination is significant.The problems of direct ingress may beovercome through the use of designsthat include concrete aprons, concretelinings, raised headwalls and covers.Nonetheless, it is often difficult toensure that the linings are watertightand ingress of water through the liningat the upper levels is common. Wheredug wells have been installed in othercountries with heavy seasonal rainfall,difficulties have been found inmaintaining microbial quality in wetseasons. The few available studiesindicate that this more often due topoor maintenance of the headworksthan from sub-surface leaching from,for instance, pit latrines.
Risks may be further reduced byensuring a sanitary means ofabstraction from the well, eitherthrough use of a handpump or bywindlass and bucket systems. In thelatter case, however, theory is muchbetter than practice as commonlydesigns where the bucket need nevertouch the ground are rapidly modifiedby users to maximise their user-friendliness. Pumps installed on dugwells have proven in many cases to
provide significant improvements inquality.
In addition to the need for goodoperation and maintenance, risks canbe further reduced by installing asystem of chlorination or where ahandpump is used, to install a filter atthe base of the well covering thescreen.
Chlorination could well be limited toonly the monsoon season when riskswould be expected to significantlyincrease. Projects in other countrieshave shown that chlorination can beeffective, but requires good trainingand follow-up. In some areas it islikely that dug wells may becomeinaccessible during flooding and wouldalso become heavily contaminated. Inthese situations, emphasis duringtraining must be given to the need fordisinfection of the well prior to re-starting use in the dry season.
As noted by UNICEF Bangladesh, itmay be more appropriate to considerrenovation of dug wells rather thanconstruction of new wells. In bothcases, evidence would be required thatthe shallow aquifer was not arseniccontaminated.
3.5 Deep hand tubewellsDeep hand tubewells have beenidentified as an attractive emergencyresponse measure. This is in partbecause of the limited evidence ofarsenic contamination of the deepaquifer and because in parts ofBangladesh there is a significantaquiclude/aquitard between theshallow and deep aquifers that shouldminimise the potential for leachingprovided construction is properlycarried out. There is a recognition ofthe need to ensure designs are effective
in preventing leaching withinBangladesh and recommended practiceis outlined in available documents.
In terms of risk substitution, deep handtubewells are attractive, becausemicrobial contamination is relativelyeasy to prevent through goodwellhead/sanitary completion and byrestricting pollution within protectionzones. Wellhead completion isrelatively easy and cheap to assureduring construction and require only
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limited maintenance to prevent rapidcontaminant pathways developing.
Despite the generally positiveprognosis of the use of deep handtubewells, reservations remainregarding their use as an emergencymeasure. In some parts of Bangladesh,notably the coastal area, the deepaquifer has been exploited for manyyears and has not shown arseniccontamination. Use of deep handtubewells in these areas is therefore asensible option.
The same situation was largelyassumed to be the case in other parts ofBangladesh, but this is becoming lesscertain. More recent testing of deeptubewells have indicated a significantproportion with arsenic contamination.
One problem with interpreting this datais the significant uncertainty regardingthe accuracy of the records on welldepth. Therefore, it is possible thatsome of the deep tubewells are in factshallow tubewells drawing water fromthe contaminated aquifer. This needs tobe clarified as a matter of someurgency.There is a current survey beingundertaken by the USGS of the deepaquifer in order to develop a betterunderstanding of arsenic movement inthe sub-surface and the scale anddegree of arsenic contamination in thedeep aquifer. Until this study iscompleted, it would seem unwise topromote deep hand tubewells as anemergency response, although theymay become more viable in the longer-term response.
3.6 Rainwater harvestingRainwater harvesting is an attractiveemergency response technologybecause it can be located at the home,thus preventing an additional burdenon women and children to collectwater and because of the abundant rainin Bangladesh. Good designs ofrainwater tanks are available andrelatively low cost.
The major risk associated withrainwater harvesting comes fromfaecal matter that may get washed intothe tank (one particular risk isassociated with Salmonella from birdfaeces). This is easily mitigatedthrough use of a first-flush diversionsystem and through cleaning of theroof and guttering. The critical time forthis is the start of the monsoon, as oncethis is underway it is unlikely that therewill be significant build-up of faecalmaterial. In rural areas it is unlikelythat there will be a significant riskrelated to chemical hazards, but this
will increase in urban areas due to airpollution from traffic. It is essentialthat the designs of rainwater systemshave meshing on the overflow pipes inparticular to prevent the water in thetank becoming a vector breeding site.
In relation to hazards from ingestion ofwater, rainwater harvesting is generallya relatively low-risk option, althoughlarge-scale studies have not beencarried out. However, as rainwaterharvesting is unlikely to providedrinking-water to last the entire dryseason, unless larger tanks areprovided. This may therefore meanthat the promotion of rainwater usemust be linked to provision ofalternative options to provide watersecurity throughout the year.Nonetheless, rainwater harvestingoffers significant potential forimprovement in water safety withacceptable risks attached.
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3.7 Arsenic removal technologiesThe NCE recommended that arsenicremoval technologies should not beconsidered in the emergency responsebecause none of the technologies hadbeen formally verified through theETV. The NCE has highlighted a rangeof benefits and disadvantages in theuse of arsenic removal technologies atboth household and community levelsand these are not reviewed in detailhere. However, it is pertinent to notethat some disadvantages highlightedwould equally apply to the watersupply options recommended.
The results of the rapid assessment ofarsenic removal technologies showedconcerns that the use of mosthousehold units were associated withan increase in microbial contaminationcompared to feed water. As discussedin the report of the assessment, this isprimarily due to poor hygiene andhandling. However, it is likely that re-contamination of water fromcommunal water sources will also becommon and many studies world-widehave shown that this occurs evenwhere households use sources of goodmicrobial quality.
Although the disadvantages noted bythe NCE are not insignificant, it isdebatable whether these are sufficientto disbar consideration of arsenicremoval technologies within anemergency response. Although none ofthe technologies has been formallyverified, for a number of thesetechnologies there is a large body ofevidence of their effectiveness inremoving arsenic. Although there maysome risk substitution for microbialhazards, this is not considered to beany greater than for any technology
where water must be transported andstored within the home.
Much of the evidence already availablefor these technologies (including fromthe manufacturers and the rapidassessment of arsenic removaltechnologies) is at least as good as theevidence of risk reduction offered byalternative water sources. In terms ofoverall health risks, it is far from clearthat the risk posed by some of theoutstanding questions is greater thanthose posed by the alternative watersources proposed.
The use of arsenic removaltechnologies at either a community orhousehold level offers significantefficiencies as an emergency response.In the case of household technologies,the capital investment costs toGovernment will be negligible andsignificant risk reductions can beexpected to accrue at a householdlevel. If the purpose of the emergencyresponse is in effect to gain additionaltime to permit the development oflonger-term improvements in watersupply, such a process is attractive.
The installation of a community leveltechnology would potentially offer notonly the short-term response but couldfeasibly develop into a longer-termsolution for communities that wereinterested in purchasing a unit. In sucha scenario, initial installation may befree of charge, but retention of the unitbeyond the immediate response wouldentail the same processes of cost-recovery as alternative supplies.Effectively, the treatment unit wouldbecome a further option that could beconsidered in a demand-responsiveapproach to long-term water supply.
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There remain issues around theoperation of community-level removalplants, notably the monitoring of theperformance of arsenic removal andthe timing of media replacement. Thisis complicated in some areas wherephosphate in groundwater competeswith arsenic for adsorption sites. Theserepresent areas where solutions mustbe found in the short to medium term,but may not be as significant in thecontext of an emergency response as
external monitoring and support couldbe provided to communities.
As noted at the start of Section 3, whenconsidering the potential for risksubstitution for alternative watersupply options, the rational forexcluding arsenic removaltechnologies appears inconsistent.Arsenic removal technologies mayprovide a viable emergency responsewhere the potential risk substitutioncan be managed.
3.8 Household treatment of water for microbial hazardsThis was not considered by the NCE,but has been raised as an option bysome NGOs and other working ondeveloping emergency interventions. Anumber of options exist forundertaking household treatment ofwater, including low-cost chlorination(notably the CDC Safe Water System),solar disinfection (for instance SODIS)and within Bangladesh thedevelopment of a system that useshousehold cooking stoves to pasteurisewater is being developed. Operationand maintenance of most systems forimproving microbial water at ahousehold level are simple.The CDC Safe Water System has beenshown to be a very effective means ofreducing diarrhoea, with a range ofbetween 25% (from a study in slums inDhaka with no sanitation) to 85% (in astudy in Uzbekistan where sanitaryconditions were poor). The data forother interventions is less welldeveloped and as these result inincreased water temperature may leadto problems with acceptability.
However, it is known that the SODISsystem may also remove arsenic.
WHO has recently completed a reviewthat concluded that this was aneffective interim solution to obtainingwater of acceptable microbial quality.There may be risks of disinfectant by-product formation if very organic-richsurface waters are used.
The promotion of low-cost householdwater treatment could accompany anyof the interventions currentlyconsidered under the emergencyprogramme. It could potentially also beused as stand-alone intervention totreat surface water, although additionaltreatment steps will be needed toreduce turbidity for disinfection andthere would be a need for ongoingtesting to ensure that it remainedeffective. This approach should beconsidered for inclusion within theemergency programme and linked tohygiene education programmes.
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4.0 Ongoing surveillance and support
The development of ongoingsurveillance should be an essentialcomponent of the mitigationprogramme. Pilot activities indeveloping surveillance of watersupplies have been undertaken in urbanareas of Bangladesh (for exampleRajshahi and Mymensingh) by DPHEwith support from WHO and DFID viaa WEDC research project. and inRajhahi and Mymensingh from DFID(via WEDC). Work has also beenundertaken on developmentsurveillance activities for small towns.
Surveillance in urban areas hasinvolved testing of both piped and non-piped water sources for microbial andchemical quality, sanitary inspectionsof facilities and testing of householdwater. The use of surveillanceinformation has been used indeveloping improvements undertakenby City Corporations and bycommunities to improve water qualityand sanitary conditions. Bothlaboratory methods and field kits havebeen used to undertake these activities.In addition, there has beendevelopment of widespread testing ofwater quality, particularly testing forarsenic, in rural areas. A protocol forthe development of a rural waterquality surveillance programme hasbeen prepared for DPHE, whichincludes recommended parameters forinclusion, frequency of testing fordifferent technologies and householdwater, and provides an institutionalframework for surveillanceimplementation.
There is a need to develop and roll-outsurveillance programmes as part of the
mitigation programme. This will helpto ensure that operation andmaintenance of technologiesintroduced during the emergencyresponse is effective. It will alsoprovide opportunities to supporthygiene education and to use waterquality testing and as an entry for pointfor improving overall water safety. Theimplementation of a surveillanceprogramme will also greatly strengthenthe evaluation of the impact of theemergency response and in refiningpolicy and strategy for arsenicmitigation.
The surveillance programme shouldinclude testing of microbial qualityusing in the first instance E.coli orthermotolerant coliforms, butincreasing aiming to introduce otherindex organisms. Sanitary inspectionsshould also be undertaken. It shouldalso include testing of arsenic intuebwells, both those previouslyidentified as being contaminated andthose previously identified as beingarsenic safe. Other parameters as perthe protcol for surveillance should alsobe included. Ongoing collection of thisdata is important in order to assesswhether temporal changes occur inarsenic concentrations.
Surveillance programmes in rural areasshould not attempt to visit and testevery water supply on a regular basis.A rolling program of visits to watersupplies should be developed with anaim to visit each supply once every 3-5years and either stratified randomsampling or cluster sampling used toselect specific supplies to be visited.
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5.0 Summary
The table below summarises the majorissues in relation to risk substitutionand the potential for control withindesign and construction and operationand maintenance. This table does notattempt to rank the technologies withregard to their use, which has beendone by the NCE, but simply sets outwhat issues will need to be considered.
For all technologies, ongoing supportthrough surveillance and hygiene
education will be essential to ensurerisk management is effective in thelong-term up to the point ofconsumption.
It is recommended that arsenic removaltechnologies, particularly those thatwork at a community level, beconsidered as an option for theemergency response.
Technology Risk substitutionpotential
Control throughdesign &construction
Control throughO&M
Pond sandfilter
Certain and high formicrobes; potentialfor cyanobacterialtoxins & chemicals
Control may bedifficult to achieveunless new designsdeveloped
Essential,significantpotential for riskincrease with poorO&M
Dug well Certain for microbes;potential forchemicals
Control can beachieved, but likelysome risk will remain
Essential,significantpotential for riskincrease with poorO&M
Deep handtubewell
Limited potential formicrobes and arsenic
Control can beachieved for microbes,uncertain for arsenic
Important formicrobes;insignificant forarsenic
Rainwater Certain for microbes,potential forchemicals from air orroofing; potential forvectors
Can achieve controlfor microbes, noimpact for chemicals
Essential formicrobes; noimpact forchemicals
Community-level arsenicremovaltechnologies
Potential formicrobes to substitute
Can achieve controlfor both arsenic andmicrobial quality insome technologies
Essential forarsenic; importantfor microbes
Householdtreatment formicrobialquality
Potential for THM iforganic-rich surfacewater used
Can achieve controlfor microbes andTHMs
Essential formicrobial andchemical quality
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Annex 1: Water safety issues and examples of ‘model’ Water Safety Plans
This annex provides an overview of how the microbiological quality of drinking water maybe controlled through protection of water sources, control of treatment processes andmanagement of distribution and handling of water. It uses the principles of water safety plansand provides guidance on how WSPS and codes of practice can be defined for a range ofwater supply technologies and for household water handling and storage. For a range oftechnologies, ‘model’ water safety plans are defined.
WSPs should be subject to approval by the regulatory body who should have access to arange of statutory tools to impose penalties for non-compliance. This may be in response tofailure to prepare an adequate management plan or failure to comply with it once established.However, as with all regulatory regimes, flexibility will be required and a range of other tools(relaxations, exemptions etc) may also be needed.
In some circumstances national or regional authorities may wish to establish a suite of basicmanagement plans to be used by local suppliers either directly or with limited adaptation.This may be of particular importance when the supplies are community-managed. Forcommunity managed supplies, an approach focusing on ensuring operators received adequatetraining and support to overcome management weaknesses will be more effective thanenforcement of compliance.
Hygiene codes are also presented for household treatment of water and water hygiene. Theseshould by used in conjunction with education programmes as a way of promoting goodhygiene. However, there should also be enforcement of minimum design criteria bymanufacturers of water treatment technologies.
The following sections provide examples of outline management plans for some of the morefrequent types of supply. In many cases several components may be needed to prepare anoverall management plan. Thus for piped supplies it may be appropriate to link themanagement plan components of source protection and treatment with those for distribution.Where water supplies are not continuous, then household management of water will be animportant additional component to be included.
The hygiene codes that follow are indicative and should be modified to meet local needs andto suit local conditions. Hygiene codes are presented for the following types of water supplyand household management of water:
1. Tubewell from which water is collected by hand2. Spring from which water is collected by hand3. Simple protected well4. Rainwater catchment5. Storage and distribution through community managed piped systems6. Groundwater from protected boreholes/wells with mechanised pumping7. Household handling and storage of water8. Household disinfection9. Household filtration systems
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In each section there is an initial introduction to provide an overview of the situations whenthe type of supply may be found and the evidence of health risks derived from the use of thetechnology. Each section then addresses four groups of issues.
Selection of reference pathogens and assumptions made. These sections provide an outlinefor the basis of identifying key challenges to health and therefore the water resource, designand control measures required to minimise the risk to public health. The reference pathogensrelate to those discussed in a report of a WHO meeting on regulation of microbiologicalquality held in Adelaide, Australia, 2002, but it should be noted that not all these pathogensare applied to all technologies.
Hazard assessments. These sections review the process of conducting a qualitativeassessment of hazards that may cause contamination of the water supply. For surface watersthis means an assessment of the catchment and for groundwater an evaluation of the rechargearea. In groundwater hazard assessments, the type of aquifer must be taken into account.
IWRM and regulatory issues. This section outlines the major controls that should be in placeat national and regional level in order to enable local action to be effective. These are aspectswhich may be outside the direct control of the supply agency itself but which are important tothe management plan. These primarily concern national legislative frameworks, local lawsand integrated water resource management. They also cover basic issues of importance suchas training needs.
Design Issues. This section looks at the basic design criteria required to ensure the adequacyof the installation to provide water reaching water quality targets. Many design issues are alsocontrol measures in a water safety plan.
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Small, community-managed point source groundwater suppliesThe following drinking water quality management deal with a series of small, usuallycommunity-managed water supplies that use shallow groundwater. These supplies are mainly‘point’ supplies – i.e. water must be collected from the source by hand.
The majority of these supplies are to be found in low and middle income countries, althoughoccasional examples may be found in wealthier countries. Whilst such supplies are generallyconsidered to be found primarily in rural areas, there are very large numbers of such suppliesin poor urban and peri-urban settlements throughout the developing world. This includessmall towns as well as some of the World’s largest cities such as Dhaka. The use of suchsupplies may not be the preferred water supply solution in such situations, however, thereality is that millions of people in cities worldwide have little prospect of access to treatedpiped water in the short term. This emphasises the need to address the quality of all suchsources whether urban or rural.
The nature of community-managed supplies also suggests that while engineeringinterventions may do much to reduce risks, training and support to communities in watersupply management is likely to be more critical and this should not be neglected by the watersupply and surveillance bodies.
The collection of water from such sources by hand implies that controlling the quality of thewater at these sources will not be sufficient on its own to reduce water-related health risks toan acceptable level. Additional interventions are also likely to be required in water handlingand potentially household water treatment as discussed further below.
Selection of reference pathogens and assumptions madeThe selection of reference pathogens and key assumptions do not significantly differ betweenthe different types of technology and are therefore presented here. The comments willtherefore apply to the next three drinking water management plans.
Critical to the establishment of water quality targets for point source groundwater supplies isan understanding of the movement, survival and attenuation of different pathogens within thesub-surface environment. For a full review of this please consult Chapter 3 of the monographProtecting groundwater for health.
Evidence suggests that control of the risk posed by viruses in groundwater is difficult toachieve solely through land-use control and wellhead protection measures. There is goodevidence of greatly extended survival and travel of viruses within the sub-surface andattenuation processes may only retard and not remove viral pathogens. One consequence ofthis is that elution of viral pathogens may occur due to changes in environmental conditionscaused by recharge. Therefore, for greater confidence that risks from viruses have beencontrolled, contact disinfection is likely to be required. Whilst the land-use control measuresoutlined below provide some confidence in reducing viral risks (particularly at the longertravel times) this may not reduce levels to those deemed acceptable. Furthermore, suchcontrols may not be feasible even when using vertical as well as horizontal flow in manysettings and therefore an elevated residual risk from viral pathogens may need to be tolerated(ARGOSS, 2001). In most cases, as first exposure to viral pathogens is likely to occur duringchildhood rather than adulthood, control of virological quality may be less urgent. In mostcases, unless disinfection is practised this would be difficult to achieve.
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The principal basis for the control of microbiological quality of these supplies is in relation torisks posed by bacterial and protozoan pathogens. For bacterial pathogens, E.coli 0157 isused. The measures put in place to reduce risks from E.coli 0157 would be adequate to dealwith other bacterial pathogens. Cryptosporidium parvum is used as the reference pathogen forprotozoan agents as it has been shown to be present in some groundwater supplies.
Hazard assessmentsHazard assessments for point water supplies should, like for most water sources, beundertaken prior to construction and commissioning of the source and on periodic visits tothe source. This will usually be undertaken through a sanitary inspection. Initial hazardassessments should be used to plan and design the water supply. It may be that hazards existthat are associated with a significant risk due to distance from proposed water source orbecause of flow rates. In such cases, risk management strategies may require careful thoughtsuch as deepening the intake.
IWRM and regulatory issuesThe IWRM and regulatory issues for all three principal forms of point water supply fromgroundwater sources are covered in a single section here as they are all basically the same.The linkages between some key IWRM issues for point groundwater sources and thoseidentified for deep boreholes with mechanised pumping should be noted. Groundwatermanagement and protection strategies should cover all forms of groundwater abstractionfound within the country and it is important that shallow point sources of groundwater are notdisadvantaged by measures to protect deeper abstraction.
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Issue Justification/explanation (includes cross-referencing to support texts for checkingin finalisation
Appropriate actions
Groundwater assessment andmapping
Critical to control of water quality ingroundwater is to understand the nature ofthe groundwater regime and the unsaturatedzone.
Legal basis for groundwaterprotection established with leadagency identified.
The need for a defined legal mandate iscrucial for protecting groundwater. A leadagency is needed to develop policy andimplement strategy.
Institutional analysis toidentify lead agencyGroundwater issuesincorporated into waterresource legislationStatutory power definedand statutory instrumentsestablished
National groundwater managementand protection strategy developed
Strategies that incorporate concepts ofvulnerability of groundwater. Within areasdefined as vulnerable, land-use controlmeasures will be required and groundwaterabstraction are controlled.
Determine protectionzone basis (usually afunction of travel time)Review groundwatermaps and delineateprotection zones
Protection areas/set-back distancesestablished based on local conditions
In each area protection areas or zonesshould be established on an understandingof the groundwater flow, potential forattenuation and engineering measuresavailable for mitigation.
Minimum safe distancesdefined for each type oftechnology and aquifertype defined
Material specification Poor quality of materials used onconstruction is closely linked withinfrastructure deterioration and waterquality failure
Minimum design criteriaestablished and enforcedMaterials allowed for usespecifiedMaterial qualitycertification
Abandoned wells and otherexcavations close to the source andwhich could affect water qualityshould be filled in
This is an important aspect to control asabandoned wells and even shallowexcavations left open may provide rapidrecharge routes into the aquifer. This maylead to either localised (source specific) orwidespread (aquifer-wide) contamination.
Requirement that all non-water excavations to befilledSpecification of cappingmaterials & techniques
Proper training of communityoperators to ensure operation andmaintenance can be performed
A significant amount of the deterioration inmicrobiological water quality can beascribed to poor operation and maintenance.Thus skills and schedules must bedeveloped to support community operators
Establish training needsEstablish trainingprogrammesEnsure tools available forbasic maintenance
Tubewell or borehole from which water is collected by handDesign issuesShallow tubewells or boreholes are used in many developing countries and are often thepreferred method of water provision in rural communities. Many different techniques existfor drilling tubewells and some of these, particularly some of the very low-cost methodsthemselves raise the risks of contamination. Tubewells are usually fitted with handpumps,although some designs of windlass have been used. A variety of types of handpump areavailable and again these may themselves represent water quality risks, particularly wherewater is need for priming. Sustaining handpump-based water supplies is often difficultbecause of associated costs and this should be borne in mind when promoting their use.
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Design issue Justification/explanation (includes cross-referencing to supporttexts for checking in finalisation)
Lining/casing of tubewell shouldextend at least 30cm above theground level/apron
If lining does not extend above the ground level or level of theplatform/apron, then wastewater or surface water may be able todirectly enter the riser pipe, leading to contamination.
The annulus around the lining/casingshould be sealed for the top 3-5metres.
This represents a highly vulnerable component of the tubewell as thismay create a direct short-circuit route into the rising main.
An apron/platform should be castaround the top of the lining (at least1m radius).
The lack of an apron/platform may allow wastewater or surface water toinfiltrate close to the rising main and cause contamination is short-circuits exist. The joint between the annulus seal and the apron shouldbe sound
Pipe joining technique Glued joints tend to be weaker and more likely to develop. Threadedscrew joints are preferred.
Handpump specification Handpumps that require priming may be more vulnerable tocontamination. Therefore lift pumps are preferred to suction pumps.
Setting screen as deep as possible Greater depth increases vertical movement of water. This tends to bemuch slower than lateral movement and therefore small increases indepth to the intake may increase travel times significantly
Drilling method Lower-cost drilling methods may reduce the possibility of implementingsome of the protection measures noted above (particularly sealing theannulus around the casing). They may still be used in soils that collapseeasily around the lining, but it is likely a significant residual risk willremain.
Filter pack placed around intake toremove suspended sediment andlarger organisms
Without filter packs suspended sediments may be able to enter the risingmain. Ingress of larger micro-organisms has occurred in someconsolidated aquifers
Disinfection prior to commissioning The tubewell should be fully disinfected by leaving a chlorine solutioninside the rising main (which by preference should be nearly full) inorder to remove contaminants introduced during sinking. Water shouldbe pumped to waste.
Surface water diversion ditchesprovided to protect against inundation
Inundation by contaminated surface water during rainfall and floodevents can lead to pathogen presence.
Wastewater from tubewell drainedaway from the riser pipe
Waste or spilt water may potentially re-enter the tubewell and carrycontamination from the surface. This may lead to introduction ofcontaminants especially if the area is not fenced. The apron should besloped away from the riser pipe and a drainage channel installed toremove wastewater away from the tubewell.
Area around tubewell and apronfenced
The lack of fencing may allow animals to damage the apron and causeflow paths to develop close to the tubewell. They may also defecate onthe apron leading to a direct hazard
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'Model' water safety plan for boreholes fitted with handpumps
Critical limits MonitoringHazardevent
Cause Risk Controlmeasure Target Action What When Who
InspectionAnalysis ofchemicalcomposition ofpollutionAnalysis of waterquality
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Protected spring from which water is collected by handSprings serve a significant proportion of rural populations in many countries and have lowercapital investment costs and usually lower maintenance requirements. Springs located uphillof communities are often linked to simple community-managed gravity flow pipe systemswhich provide greater convenience and may improve hygiene through greater water use. Awater quality management plan for such supplies has been previously outlined. In thissection, only springs that have been protected are covered as unprotected springs are open tocontamination and their use may represent a significant health risk.
Design issuesDesign issue Justification/explanation (includes cross-referencing to support
texts for checking in finalisation)Backfill properly designed andconstructed to provide adequateprotection
The area between the ‘eye’ of the spring and the outlet through aretaining wall or spring box is highly vulnerable to pollution. There isusually some distance between the ‘eye’ and retaining wall that must beprovided during construction. This area should be filled with a finegravel/sand filter matrix up to the point of maximum water rise. Thefilter should be overlain by several protective layers (fine sand, clay andgrass) to prevent downward pathogen movement during recharge. SeeGroundwater monograph.
Ditches construct to divert uphillsurface water
Direct inundation of the immediate backfilled area may lead to erosionof protection measures noted above and may lead to directcontamination by surface water. Ditches should extend some way abovethe ‘eye’ of the spring and be adequate to carry specified flood flowsbased on set return periods – see Groundwater monograph.
Spring catchment area properlyfenced and access restricted
Lack of fencing allows direct access to the backfilled areas by animalsand humans. This may lead to erosion of the protective measures notedabove and provide direct flow paths to spring outlet. A lack of fencingmay also allow human and/or animal faeces to accumulate on thebackfilled area. The areas should be fenced as far as possible, seeGroundwater monograph.
Latrines, waste disposal sites andanimal husbandry sited well awayfrom spring (based on riskassessment using attenuation, die-offand travel time concepts) andpreferably downhill
There is limited flexibility on the water source location in this contextand therefore siting of polluting activities becomes important. Thisrelates to the groundwater protection areas/zones and set-back distancesreferred to in the design issues.
Unused water from spring should beproperly drained and not allowed toinundate the spring outlets.
Drains are also required to remove water that comes from the spring andis not collected. Lack of drainage may result in flooding of the springleading to submersion of the outlet and difficulties in preventingcontamination during water collection
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'Model' water safety plan for protected springs not connected to piped water supplies
Critical limits MonitoringHazardevent
Cause Risk Controlmeasure Target Action What When Who
Correctiveaction
Verification
Contaminationable to rechargespring in backfillarea
Backfilled areabecomes eroded
Moderate/Major
Effectivespringprotectionmeasuresmaintained
Area has grasscover; fence anddiversion ditch ingood conditionNo surface wateruphill
Fence is brokenDiversion ditch isdamagedSurface waterpools develop
InspectionAnalysis ofchemicalcomposition ofpollutionAnalysis of waterquality
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Protected dug wellDesign issuesThe key design issues for dug wells that should provide basic protection against mostpathogens are outlined below. However, although exclusion of protozoan pathogens shouldrelatively easy to ensure, controlling bacterial and viral pathogens is often more problematicas ensuring impermeability of lining material is difficult. Disinfection is possible using low-cost techniques and is included here as an option that should be considered. However, itshould be borne in mind that sustaining disinfection may be difficult in low-incomecommunities and a balance should be maintained between water quality targets desired andpractical implementation.
Design issue Justification/explanation (includes cross-referencing to supporttexts for checking in finalisation)
Well lining extends above groundlevel as a parapet or wall
Increasing the height of the parapet so that users cannot put feet intowater will stop guinea worm transmission. If combined with a cover,apron and handpump, contamination by other pathogens can be reduced
Cover slab placed on top of well Placing a cover slab on the well will prevent direct entry bycontamination that is introduced from buckets. Covering the well maylead to significant reductions in pathogen loads.
Handpump/windlass/sanitary bucketsystem used to withdraw the water
Limiting introduction of many buckets prevents direct contaminationfrom dirt on the base/outside of the bucket. Handpump provides greatersanitary protection and are preferred for water quality control.
Extend apron/platform around well(preferably at least 1.5m radius) fromthe wellhead
Lack of an apron may lead to the development of short-circuit routes forwater on the surface and may also eroded the area around the well. Thismay also compound problems with permeable well linings. The apronshould be sloped away from the well to ensure that spilt water isproperly drained.
Wellhead area protected fromanimals through fencing (includingapron and immediate surroundings).
Lack of fencing will allow animals direct access to the wellhead. Thismay increase the risks of damage of apron and the potential for creatingshort-circuit flow paths into the well. It may also lead to build up offaecal matter close to the well.
Diversion of surface water away fromwell through diversion ditches
Diversion ditches should be located some way from the well and thelarge enough to carry at least 10 year return period flood. The diversionditches should encircle the well and lead the drainage water away fromthe well. The use of sumps or soakaways close to the well should beavoided.
Good drainage of spilt water from thewell
Poorly drained spilt water may form pools close to the well and lead torapid recharge into the well leading to contamination
Wells properly sited based onhydrogeological assessment of risks
Minimum set-back distances may be required to reduce the risks ofcontamination from excreta disposal facilities or solid waste dumps.This should be based on hydrogeological and microbial assessments ofrisk.
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'Model' water safety plan for dug wells
Critical limits MonitoringHazardevent
Cause Risk Controlmeasure Target Action What When Who
Correctiveaction
Verification
Ingress ofcontaminatedsurface waterdirectly into well
Well does nothave a cover;lining stops atground level;faulty or absentapron; drainageditches faulty orabsent
InspectionAnalysis ofchemicalcomposition ofpollutionAnalysis of waterquality
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Rainwater catchment
Rainwater collection is widely used throughout the developing and developed world. In low-income countries, collection is typically practised at the household level with roof collectionbeing the most common approach used. In many cases, low volumes of rainwater arecollected using makeshift gutters and open containers for use the same day or to provide alimited reserve lasting 2-3 days. The methods used in such cases are not protected andcontamination is difficult to prevent. Simple improvements in the collection, guttering andstorage containers can significantly increase efficiency and provide water reserves that canlast several weeks. Simple improvements can also greatly improve the control of waterquality and significantly reduce contamination risks. Where water is stored for longer periods(several weeks or more) then increasing problems may be found with vector-borne diseaseand sometimes taste and odour problems. Some designs are available to reduce suchproblems, although these typically increase costs.
Highly sophisticated forms of rainwater collection are used in developed countries, oftenusing specially prepared impermeable ground catchments, where rainwater feeds a treatmentplant and distribution system. Such catchments need basic maintenance and protection toprevent unacceptable build-up of pollution. A further refinement of rainwater collection thatis included for completeness is fog collection. This is applied in only a limited number ofcountries (notably Chile and Peru) but is attracting increasing attention in other dry areas ofthe world.
Selection of reference pathogens and assumptions madeWhere rainwater is collected from large ground catchments, then it is assumed that this willbe part of a public water supply supplying water via treatment works an distribution systems.This water therefore is essentially a surface water source and should meet the criteria outlinedabove for water treatment. Source protection will be important and should exclude humanactivity. However, wild animals and in particular birds may represent a particular hazard,although these may be difficult to control. A hazard assessment for such systems wouldinclude periodic surveys to ensure that:
• human activity has not encroached into the catchment or controlled areas;• no discharges of human waste occur upstream of the catchment;• solid or hazardous waste has not been dumped in the catchment or so that its leachate can
run-off into the catchment; ;• type and numbers of animals likely to be found in the catchment
For large ground catchment rainwater collection systems, the reference pathogens are thesame as those for any other surface water source and the control measures will be the same asnoted previously for treatment processes.
Household rainwater collectionAs it is generally assumed that rainwater is not microbiologically contaminated to asignificant degree, most household rainwater collection system will not undergo treatment,although some designs include filtration units (of generally unproven efficacy) or periodicdisinfection may be practised. The presence of animal and bird faeces represents a risk ofbacterial and protozoan pathogen presence. Human faeces would be unlikely to be asignificant hazard, although it is possible that this could occur where excreta disposal is poor
29
and the ‘wrapper’ or ‘flying’ latrine method is used or where contaminated water sprays canreach the catchment (for instance see Simmons et al).Roofing material may exert a significant influence of water quality, with hard impermeablesurfaces preferred to grass thatch as the latter may harbour significant microbial ecosystems(Uba and Aghogho, 2000). The first rains are likely to represent a time of elevated risk ascontamination on the roof and gutters that has built up over the dry period are washed into thecollection tank (Gould et al, 1999). Therefore the diversion of water derived from the firstrains is an important control measure for microbiological quality.
The cleanliness of the roof will be critical to avoid contamination in the rainwater tank andthis should be the primary focus of a hazard assessment. Hazard assessments will typically beregular visual assessment of cleanliness of the roof and gutters (WHO, 1997).
The principal reference pathogen of interest is E.coli 0157, as the majority of data availableon pathogen presence has suggested that bacterial pathogens (and in particular those withanimal as well as human hosts) are of greatest concern. E.coli 0157 will clearly provide agood reference pathogen in these cases. Viral risks are less certain (few studies have beenundertaken) and it would be likely that there was commonly childhood exposure to viral riskswhere widespread use of unchlorinated rainwater is practised. Furthermore, withoutdisinfection it unlikely that viral risks could be minimised in any case.
Risks of infection by cysts are also uncertain given limited data. It is likely that there ispotential for cysts derived from wild animals to be present in rainwater. However, it is notclear in what numbers cysts may be present and therefore a true estimation of risk may bedifficult. Furthermore, in many areas where untreated rainwater is widely collected, the levelof risk posed by drinking water would almost be certainly far lower than those posed bydirect human-animal contact. Some rainwater collection systems use sand filters on the inlet.The efficacy of these filters in removing microbiological contamination is far from certainand it is not clear that they could be relied upon to remove cysts. However, they do removelarger debris and so will also remove pathogens adsorbed onto particulate matter.
The combination of the above factors suggests that in most cases establishing drinking waterquality management plans for viral and protozoan risks will have limited effectiveness andmay be counter-productive by increasing costs.
The regrowth of pathogens within rainwater tanks again is not well researched but could beprojected to be significant. It is certainly possible that biofilms could be developed within arainwater tank and that this could harbour pathogens introduced through poor tankmaintenance or poor catchment hygiene. This area requires further work in order to establishwhether this is a real risk, or simply a theoretical problem.
The water quality management plan outlined below assumes that the system of rainwatercollection follows some form of improved systematic design – i.e. a tank or other container islinked to a system of gutters. It is not designed where rainwater is occasionally collected in abucket. As rainwater collection in most countries is a household activity, it is implicit that theprocess of monitoring of quality requires support from local health bodies, although the costimplications of such an approach are significant (Simmons et al, 2001).
Fog collection is a relatively new technology and is not widely practised. The risks associatedwith this are not widely reported but it can be assumed that they potentially exist primarily
30
from contamination by birds or animals. Direct control may be difficult and disinfection islikely to be the principal control measure available. However, pathogen loads would not beexpected to be high. Furthermore, in areas where fog collection is practised tend to havequantity problems in water supply and therefore undue attention on controlling drinking-water quality may be counter-productive as the primary risk may result from poor hygienecaused by inadequate volumes of water.
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IWRM and regulatory issuesIssue Justification/explanation (includes cross-
referencing to support texts for checking infinalisation
Appropriate actions
Sufficient rainfall to meetbasic needs
Rainwater collection should take into accountavailable rainfall in comparison to overall waterneeds and available sources. Rainwater use may berestricted to non-potable uses thus less stringentcontrols on quality are required. Exacting measuresfor water quality may not be either technically orfinancial feasible, nor of particular importance tohealth and may prevent use of rainwater whichwould provide benefits to users.
Hydrological evaluationof feasibility. Assesswhether rainwater can beprincipal or supplementalsource based on likelyconsumption patterns.Asses current watercollection practices anddifferential uses of water.
Zoning of groundwatercatchment
Where groundwater catchments are used to supplylarge volumes of rainwater for domestic supplies, thecontrol of land-use in areas within or close to thecatchment may help to reduce contamination. Insuch zones, sanitation technologies, waste disposal,industrial development and other hazards can becontrolled through design and constructionspecifications. However, in small island states thismay represent political problems.
Establish legal basis forland-use zones andidentify practices allowedwithin each zone type.
User hygiene education Households need training in basic operation andmaintenance and in particular the need to divert thefirst foul flush from the drinking water tank (whichmay be problematic in areas of low rainfall). Wherefoul-flush diversion is difficult, then hygieneeducation could focus on treatment of water in thehome.
Responsible agencyshould be identified andprogramme developed.Simple materials shouldbe developed to helpguide households.
Specification of catchmentsthat may be used underdifferent circumstances
Ground catchments should be avoided unless theyare linked to water treatment works. Whererainwater will be consumed untreated, then only roofcatchments should be used. Thatch catchmentsshould not be used when water is used directly forconsumption.
Establish a set ofregulations for catchmentsthat may be used forwhich purposes. These arelikely to only coverconstruction and apply toagencies promotingrainwater catchment.
Materials specification The materials that can be used to seal tanks andtransport water through gutters should be specifiedto bacterial colonisation to reduce biofilmdevelopment.
An overall assessment of water quality should beundertaken to identify whether any major qualityissues may derive from air pollution. This need notprohibit rainwater use, but risks should be properlyunderstood from the outset.
Undertake assessmentbased on prevailing windand industrial discharges.Air quality assessmentmay also be needed.
Definition of responsibilityfor routine surveillance andmonitoring
As rainwater collection tends to be household (asopposed to community) focused, support is likely tobe required for ongoing monitoring. This should belinked to operation and maintenance and hygieneeducation.
Identify national and localagencies.Identify NGO/ CBOs thatcould perform supportrole.
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Design issuesNote that many design issues are also control measures and are repeated on the table ofverifications
Design issue Justification/explanation (includes cross-referencing to supporttexts for checking in finalisation)
Tank is above ground Tanks that are fully or partially underground have a greater risk ofcontamination, for instance through leakage via weaknesses in the tank.They are also more difficult to clean without pumping out of all washwater.
Tank is watertight Tank should not allow any water to enter the tank other than through theinlet from the gutters. The join between the inlet pipe and tank shouldbe properly sealed and not allow contamination to enter. Reducing theamount of light entering the tank may also inhibit algal development
Tank has drain valves to allow propercleaning and drainage of wash water
It should be possible to completely drain down the tank and for dirtywater to be removed during cleaning. Drained water should be removedfrom the tank and flow to a soakaway or drain.
Tank has tap or other hygienicwithdrawal system
Unhygienic removal of water from the tank may introducecontamination into the tank. A tap is preferred as this limits directcontamination potential, but the join to the tank should be properlysealed. Water should not be directly drawn from the tank by a bucket toprevent direct contamination.
Tap or draw-off point at least 5cmabove base of tank
Such a height difference allows debris to settle on the floor of tank andmay reduce pathogen loads in the body of collected water
First flush diversion systems in place Foul-flush systems allow the first rains collected from the roof whichare more likely to be contaminated to be drained to waste. However,whilst this may reduce bacterial loads, it may not completely eliminatethem. The design should be simple and easy to use. In cases where thereis very limited rainfall, care should be taken to ensure that foul-flushdiversion does not seriously compromise the amount of water to becollected. If this is the case, then alternative strategies (e.g. treatment)should be used.
Some form of filter to remove largerdebris
Sand and gravel filters may be adequate to remove larger debris (forinstance leaves etc) which may have a positive effect on water quality.However, these are unlikely to remove all pathogens.
Roof is hard impermeable surface Hard impermeable surfaces increase the potential for cleaning andreduce the potential for microbial ecosystems to develop
Drainage of roof and gutter washwater away from tank
When the roof and gutters are cleaned, the dirty water should not flowinto the tank but should be diverted into a soakaway or drain
Tanks should have adequate access toensure proper cleaning
As the inside of the tank should be scrubbed during cleaning to ensureall accumulated
Trees do not overhang roofs used forcollection
Avoiding direct overhang of roofs used for collecting rainwater by treeshelps reduce the likelihood of bird or rodent faeces building up on theroof
Cover all vents etc with mesh Putting mosquito and other fine mesh material on the inside of all airvents and overflow pipes reduces potential for direct access to the tankby small animals and also reduces the potential for mosquito breeding
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'Model' water safety plan for rainwater collection no disinfection as standard
Critical limits MonitoringHazardevent
Cause Risk Controlmeasure Target Action What When Who
Correctiveaction
Verification
Bird and animaldroppings foundon roof or inguttering
Roof is notcleaned properlyor regularlyallows build-up offaecal material
Water withdrawnusing bucketswhich introducecontamination
Almostcertain/Minor
Install tap orother sanitarymeans ofwithdrawal
Tap in place toallow easywithdrawal ofwater
Lack of tap Sanitaryinspection
On installation Owner/Operator
Install tap withintake at least 5cmfrom base of tank
Sanitary inspectionTurbidity
E.coli
Faecal streptococciTank is damagedor allowscontaminatedsurface water orgroundwater toenter
Tank has cracksand other damage
Likely/Minor
Structuralintegrity oftank
Tank set aboveground and ingood condition
Cracks in tankstructure
Sanitaryinspection
Annual Owner/Operator
Effect repairs Sanitary inspection
34
Roof materialintroduced intotank
Collection surfaceis soft and allowsmaterial to beleached into thetank
Likely/Minor
Only use hardsurfaces forrainwatercollection
Collection fromimpermeablesurfaces
Collection fromthatch and othersoft surfaces
Sanitaryinspection
At installation Owner/Operator
Replace roofmaterial
Sanitary inspectionTurbidityColour
Water is notfiltered
Water enters intotank with nofiltration
Likely/Minor
Filterinstalled andmaintained
Tanks haveworking filterinstalled toremove debris
Lack of filter,increased turbidity
SanitaryinspectionTurbidityColour
Annual Owner/Operator
Install filterClean filter
Sanitary inspectionTurbidityColour
Leaching ofchemical fromroof material intowater
Roof materialcontains lead orother harmfulchemicals
Unlikely/Minor
Materials forrainwatercollectionapproved
Roof materialshould not containlead or otherharmfulsubstances
Roof materialknown to containlead or otherharmful chemicals
Inspection ofmaterials
At installation Owner/Operator
Use lead-freeroofing material
Inspection ofmaterialsAnalysis of lead andother chemicals ofconcern
35
Storage and distribution through community managed piped systems
In many parts of the world, simple piped water systems are managed by communities. Suchfacilities are typically fed by gravity and are often drawn from groundwater sources such assprings. In these cases, treatment or disinfection of drinking water is rarely undertaken. Somesupplies are also drawn from upland streams where again no treatment or disinfection isperformed. In some communities, a mechanised borehole feed a small tank and distributionsystems are used. In some cases community managed treatment plants linked to thedistribution system are used. Many control measures and management actions are similar tothose in the previous section, but are covered here as the absence of disinfection may increaserisks.
Selection of reference pathogens and assumptions madeThe hygiene code outlined below is based on an assumption that the source is protected insome form and that there is no disinfection of the water prior to distribution. The selection ofreference pathogens reflects the likely socio-economic conditions within communities, whichare primarily small, rural communities in developing countries. In these communities, firstexposure to viruses may be expected to be more likely to occur in childhood rather thanadulthood and therefore whilst viral risks should be controlled as far possible, withoutdisinfection this will not be fully effective. Cryptosporidium control will be focused primarilyat the source and would not be expected to be of great importance during distribution.Furthermore, exposure is likely to occur through other routes and this should be borne inmind. Re-growth may be controlled through pipe materials, but there will be little or noalternative control measures available and therefore Legionella pneumophila is notconsidered as a reference pathogen. As a result, the principal focus of the measures outlinedbelow will be to control risks from E.coli 0157, although it is expected that many of thesemay also have a positive impact on the other pathogens.
Hazard assessmentsThe hazard assessment for small community-managed systems will have many of thecharacteristics of those for utility-managed distribution systems. However, the focus will beon the above ground sources of faecal matter in the environment and the physical state of theinfrastructure rather than estimating biological stability. Such an approach requires regularsanitary inspection by ‘walking of the line’.
36
IWRM and regulatory issues
Issue Justification/explanation (includes cross-referencingto support texts for checking in finalisation)
Appropriate actions
Water source shouldhave adequate capacityto meet demand pluslikely level of systemlosses
One of the major causes of deterioration in water qualityis discontinuity or rapid pressure loss in systems whichincreases the potential for back-siphonage. This mayrequire storage of water where yields are insufficient.
Assessment of demand.Ensure that sources aredeveloped with potentialto meet demand plusleakage.
Development of hygienecodes of practice forinstallation ofdistribution systems
Hygiene code of practice prepared for use by allagencies and companies constructing community-managed gravity-fed systems.
Hygiene code of practiceprepared anddisseminated.
Training of communityoperators
Poor training may lead to fail to operate and maintainsystem properly. This should include basic monitoringtechniques and O&M programmes.
Training programmesdeveloped.
Ongoing support throughsurveillance andmonitoring.
Ongoing support through surveillance and monitoringwill help communities to sustain operation andmaintenance and reduce the risks of contamination.
Ongoing supervisionsystems in place tosupport communities bywater supply and/orsurveillance bodies.
Design issuesMany factors will influence the design of a piped water system, including ensuring theresulting cost of water remains affordable, that demand can be met and losses are minimised.The control of water quality must be set against decisions relating to affordability andimprovement in access. However, designs to improve water quality and in particular thosethat relate to ingress of contamination water are all likely to also have a positive impact onreducing losses and improving user perceptions of the service. The latter may be importantwhen trying to improve overall access.
Design issue Justification/explanation (includes cross-referencing to supporttexts for checking in finalisation)
Source used is protected according torelevant hygiene code.
Entry of contaminated source water may be the major problem and thisshould be avoided through good design and construction.
Storage tank included in systems tosustain pressure and meet peakdemands. All tanks should be coveredand located away from trees.
Where storage tanks do not exist, peak demands may result in lowpressure or discontinuity within the supply and increased risks ofcontamination due to back-siphonage. Tanks should be covered andlocated away from trees for the same reasons as for utility servicereservoirs.
Washout and bypass systemsincorporated into service reservoirdesign
Poor design of service reservoirs that make access and cleaning difficult(particularly the removal of wash water) makes hygiene difficult tomaintain and may encourage contamination
Low biofilm adherence materialsused for supply pipes (uPVC etc)
Pipe material is noted as being important in promoting biofilmformation.
Selection of jointing materials andmethods
High quality jointing materials will reduce the likelihood of leakagewithin the supply and therefore reduce the potential for back-siphonage.
Sluice valves on sections of pipe When repair to pipe system being undertaken, isolation of sections ofmains pipe essential to prevent large scale contamination
Specification of materials allowed foruse in drinking-water mains
Materials approved for use in drinking water mains should not readilysupport microbiological communities.
Proper drainage around all valves,junctions etc
Direct inundation from flooded valves may introduce contaminationinto the distribution system. All valve boxes should have a permeablebase to allow rapid drainage of water.
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'Model' water safety plan for community managed distribution systemCritical limits MonitoringHazard event Cause Risk Control
measure Target Action What When WhoCorrectiveaction
Take source off-line and applyappropriatecorrective action(see appropriateWSP)
E.coliFaecal streptococciBacteriophagesTurbidity
Microbialcontamination ofstorage tank
Birds/animalcontamination ofstorage tanks
Unlikely/Major
Make suretank is animaland bird-proof
Vents covered,inspection coversin place andlockedNo tree branchesoverhangreservoir.Fence aroundtank
Vent orinspection coversnot in place ordamaged; fencedamaged, treebranch encroachon tank
Sanitaryinspection
Weekly/Monthly
Communityoperator
Vents should bedesigned so as toprevent directaccess andcovered to preventaccess from smallbirds and rodents.Tree branchesshould be cut-back and the sitemade secure.
Leaks in pipecombined withdrops in pressure(eitherintermittence ortransient pressurewaves) allowingress of watercontainingpathogens fromfaecally-contaminated soils
Poor hygiene inrepair work allowscontamination toenter into thesystem
Moderate/Catastrophic
Hygieniccodes ofpracticefollowed
Hygiene codedeveloped andtraining providedto all peopleworking onsystem
Evidence thathygiene code notfollowed
TurbiditySite inspection
As required Communityoperator
E.coliFaecal streptococciBacteriophageHygiene inspectionReview ofmaintenance records
39
Groundwater from boreholes with mechanised pumping linked to a distribution system
It is generally assumed that such facilities will be operated by a public entity/utility charged withthe supply of drinking water and will therefore have sufficient operational capacity to undertakeproper design, construction, operation and maintenance. It is expected that such supplies will beregulated and compared to enforceable water quality targets/standards. It should be noted that therecommendations here regarding disinfection relate solely to the production stage of water takenfrom groundwater and not to distribution.
Selection of reference pathogens and assumptions madeA full discussion of the survival, transport and attenuation of pathogens in groundwater is given thebackground monograph. Hepatitis viruses and Cryptosporidium parvum are of particularimportance as the control of risks from these pathogens would be likely to resolve the problems ofbacterial pathogens. However, E.coli 0157 is retained as a reference pathogen specifically because itinclusion allows a greater flexibility in defining levels of tolerable risk and in land-use control.
The principal challenges in groundwater posed by viruses relate to extended potential survival andmore limited potential for attenuation. Attenuation is highly dependent on environmental factors inthe sub-surface and often only retards, rather than eliminates viruses. Retardation may be reversible.In most situations where the water supply from the groundwater source undergoes at leastdisinfection and subsequent distribution, overall socio-economic development and environmentalhygiene are often also good. This suggests that first exposure to viruses in adulthood may be morelikely.
Whilst control of viral hazards through land-use control is desirable for all groundwater supplies, itis also important to recognise that this may not be adequate to reduce risks. Chapter 3 in thebackground monograph indicates that viral survival may be greatly extended in comparison to otherpathogens. The evidence suggests that once travel times from point of entry into the water body tothe point of abstraction exceeds 50-60 days, then the processes of attenuation and die-off result insignificant reductions in pathogen densities and therefore the probability of exposure throughingestion of water are greatly reduced. However, a residual risk is retained and in countries withlimited alternative childhood exposure routes may be greater than acceptable. In thesecircumstances, reductions in viral risks can only be achieved through contact disinfection prior todistribution.
With the exceptions of karstic or other fracture dominated aquifers, removal of cysts duringrecharge is likely to be rapid and primarily a function of filtration. In such cases, the principalmeans of control will be to ensure that direct entry into the borehole caused by poor completion ofsurface headworks and the first few metres underground is prevented.
In aquifers dominated by fracture flow, detailed knowledge of the hydrogeological regime arerequired to estimate risks. Cysts have relatively long survival times (see microbial quality review)and in groundwater systems that have limited filtration capacity it is likely that protozoan cysts willbe able to travel extended distances in an infective state. However, for karstic systems, there is arational for considering these to be surface waters that require full treatment (see groundwatermonograph).
In general the measures that are adopted to prevent protozoan and virus contamination of drinkingwater should be adequate to reduce risks from bacteria to an acceptable level. Survival of bacteria ingroundwater is significantly lower than for viruses (see microbial review) and attenuation isgenerally more effective given the greater size of bacteria and increased potential for mechanismssuch as microbial predation (see Chapter 3, groundwater monograph).
40
Reductions in bacterial density occur relatively rapidly and thus the probability of exposure throughwater to numbers of bacterial pathogens likely to result in infection is reduced rapidly. Theapplication of protection zones geared towards reducing bacterial risks are likely to be effective.Travel times of 50 days would usually be more than adequate and shorter travel times (for instance25-30 days) may be adequate (Groundwater monograph, Chapter 3). This suggests that land-usecontrol measures may be sufficient to reduce risks to an acceptable level and that contactdisinfection designed to inactivate bacterial pathogens should not be required.
There is good evidence that bacterial contamination occurs due to poor wellhead completion.However, the controls put in place to prevent direct ingress designed to control cysts would beexpected to reduce bacterial pathogens to an acceptable level, particularly where these increasevertical movement to the point of intake.
However, measures specific to bacterial pathogens are included here for two specific reasons.Firstly, for many countries, control of epidemics remains the primary goal of water qualitymanagement and therefore control of bacterial pathogens is an important goal. Secondly, in settingwater quality targets in relation to endemic disease which are based on design measures, the use ofbacteria (particularly where protection zones are a key control point) could be used when setting alower (but still acceptable) water quality. This approach supports the principle of local decision-making based on a tolerable disease burdens, available resources and targets for health. Thereference bacterial pathogen used is E.coli 0157 as there is strong evidence of link to outbreaks.
Hazard assessmentsThe hazard assessment would normally take the form of a sanitary survey of the catchment area andof the integrity of the infrastructure of the borehole, in particular at the wellhead. However, whentranslating the hazard assessment into a risk assessment, the hydrogeological environment andvulnerability of aquifers should also be taken into account to ensure that a realistic assessment canbe made of the risk and its severity. This is of particular importance for groundwater as the natureof the aquifer will determine whether a hazard represent any risk to the water supply.
There are many potential sources of faeces within the environment that may represent a hazard.These include on-site sanitation (septic tanks, pit latrines), sewers, landfill sites, waste dumps andscattered waste, land applications of sewage sludge, animal husbandry and slurry pits. The hazardmay be underground (e.g. on-site sanitation, sewers, landfill sites) or may be on the surface (e.g.waste dumps, animal husbandry and slurry pits). The nature of the hazard needs to be consideredwhen undertaking a risk assessment and attention paid the likelihood of pathogen reductionsthrough attenuation, die-off and dilution.
41
IWRM and Regulatory issues
Issue Justification/explanation (includescross-referencing to support textsfor checking in finalisation
Appropriate actions
Exclusion of polluting activities fromsurrounding area (transport ofpathogens to well). This includes allsources of pollution that may releasepathogens into the groundwaterenvironment. This will include on-site sanitation, animal husbandry,slurry pits, sanitary landfill sites,waste dumps and graveyards. Theremay also be a need to consider thecontrol low-intensity livestockrearing in sensitive areas.
Groundwater mapping andassessment of vulnerability.
Borehole archive established tostrengthen groundwater database.
Water supply and water resourcemanagement agency have veto onacceptable developments withinrecharge areas
Licensing of drilling agencies andcertification on commissioning
Proper remediation of abandonedwells.
Pathogens and other pollutants may beable to travel significant distances andsurvive for extended periods withinthe sub-surface environment.Retardation rather than eliminationmay significant for viruses andsubsequent elution may beproblematic.
Groundwater flow regimes must beunderstood in order to defineprotection measures.
Borehole archive provide usefulinformation about aquifers andvulnerability and support groundwatermapping.
Changes in land-use may introducepathogens into recharge areas thatresult in contamination.
Licensing of drilling agencies allowsgreater regulatory control of drillingpractice and reduced risk of sub-standard performance.
Abandoned wells provide rapid short-circuit routes for pathogens in theaquifer and may cause widespreadcontamination.
Establishment of legislativebasis for groundwaterprotection zones (seegroundwater volume).Establishment of legalframework for land use control.Set-back distances defined foron-site sanitation.Allowed stocking densitiesdefined and enforcedLandfills prohibited in rechargeareas
Groundwater mappingprogramme established andrecords held.
Borehole archive establishedwithin Government or licensedagency.
Effective local procedures forland use change approval.
Licensing system developed,with procedures forapplication, approval andcertification.
Regulations for sealing ofabandoned wells established.
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Design issuesThe proper design of the facility is critical to protecting the borehole against ingress of pathogens.Wellhead completion and control measures in the immediate area are critical to reduce the risks ofpathogens entering the supply. However, these measures should be supported by the developmentof a groundwater protection policy noted above.
Design issue Justification/explanation (includes cross-referencing to supporttexts for checking in finalisation)
Minimum standards for constructiondefined
Direct ingress of pathogens may occur where wellhead completion ispoor. Setting minimum standards that are enforceable with regulationsis important to ensure quality.
Materials specification for use inbelow ground infrastructure.
The use of poor materials may lead to cracking or damage in belowground infrastructure, providing short-circuit routes for pathogens.These should be enforceable.
Well casing should extend above theground level (e.g. 30cm/18 inchesetc) and annulus sealed at surface
Contaminated water may be able to directly enter the casing if this isbelow or at ground level. By raising the casing above the level of likelymaximum inundation, direct entry from the surface can be prevented(see Groundwater Monograph, Chapter 2.4 and 12.2)
Seal annulus around well lining to aminimum depth (at least to belowfirst joint – usually 5m). Inconsolidated formations, seal shouldextend to the top of the intake screen
Unsealed annulus may allow direct ingress of surface water intoborehole or may allow short-circuiting of surface water with limitedattenuation potential. Evidence of contamination by direct ingress/shortcircuiting of lining is provided in Groundwater monograph in Chapters2.4 and 12.2.
Ensure cracks/weakened joints arenot formed in the casing or lining
Cracks in casing/lining materials may allow short-circuit routes forcontaminated surface water. Joints in casing materials are particularlyvulnerable to wear.
Surface plinth extending minimumdistance (at least 2m radius) aroundwell.
The ground surface around the casing should be sealed and theapron/plinth designed to slope away from the casing so that spilt wateris directed away from the well. If no apron/plinth exists, a direct ingresspath may develop for surface water short-circuit routes that minimisefiltration times may also develop. Evidence for contamination of wellswithout plinths or with cracked plinths exists, see Groundwatermonograph.
Exclusion of animals andunauthorised people to minimumdistance from wellhead for at least10m.
Lack of exclusion may allow both deterioration of the immediateenvironment around the wellhead which may cause damage to thewellhead or development of short-circuit routes. Access by animals maylead to a build-up of faecal matter close to the wellhead. There is goodevidence that a lack of exclusion may contribute to contaminationevents.
Drainage adequate to prevent surfacewater flow travelling to immediateproximity of wellhead. Ditchesshould be set a minimum distanceuphill (e.g. 10m)
Lack of surface water diversion increases the risk for direct inundationof the wellhead by contaminated surface water and may lead to directingress of contaminated water. Repeated flooding may cause erosion inthe immediate wellhead area and the development of short-circuit routesfor pollutants. There is evidence of poor drainage contributing tocontamination of wells.
Application of contact disinfectantusing an appropriate Ct value
Protected wells may remain vulnerable to occasional contamination andin particular reduction of risks for viruses may be particularly difficultto guarantee. Reducing risk from viral contamination is likely to requirecontact disinfection. Automated continuous monitoring with permanentretention of records at larger installations. At smaller installationsfrequent analysis and record keeping.
Sluice valve prevents back-flow intoborehole.
When pumping from the borehole ceases, water within the distributionsystems will be at higher pressure and may flow back into the borehole.
Distribution See section on piped distribution
43
'Model' water safety plan for mechanised boreholesCritical limits MonitoringHazard
eventCause Risk Control
measure Target Action What When WhoCorrectiveaction
Inspection Operator Weekly Ensure all drainsproperly sealed inrecharge orvulnerable areas
Audit of drainagechannel design,construction andmaintenance
Industrialdischargescontaminatedgroundwater
Poorly disposedof industrialwaste caninundategroundwatersource or leachinto aquifer
Moderate/Minor
Wastecontainmentand treatment
Effective disposalmethods preventspills and leaching
Waste disposalmethods do notprovide securityagainst inundationand leaching
Monitorcontainmentmethods atindustrial sites
SupplierEnvironmentagency
Monthly Ensure allindustrial waste isproperlycontained andtreated at the site
Audit of industrialwastewatertreatment plants
46
Household handling storage and treatment of water
The safe handling and storage of water within the home is the final component of a safe waterchain. Evidence from around the world suggests that this step is critical and that investments madein improving water source protection, treatment and distribution may not lead to significantimprovements in health if household handling and storage is poor. In this section we deal both withstorage of water in tanks within houses that are connected to a piped water supply and for storage insmaller containers when water is collected from a communal source of water.
Outbreaks of infectious diarrhoeal disease have occurred in both developed and developingcountries resulting from contamination of plumbed in storage tanks in blocks of flats.Contamination of a storage tank by bird faeces has been a common problem. Poor storage andplumbing within buildings has also led to regrowth or bacteria and contamination with Legionellaspp. remains a major problem in many countries. In these cases, interventions are primarily relatedto good operation and maintenance of water systems within buildings.
In addition to the problems noted above in relation to plumbing and large-scale storage withinbuildings, recontamination of water during collection, transport and storage when water is availableonly from a communal public water source are also widely reported (see background paper for moredetails). However, whilst clearly a significant problem, many of the studies indicating suchproblems have focused on indicator bacteria as opposed to pathogens. The relative importance ofrecontamination of water by pathogens has been questioned, given obvious greater potential forspread by other intra-familial routes (notably food) and likely acquired immunity (Vanderslice andBriscoe, 1995). However, control of recontamination is likely to be a key measure in reducinginfectious disease transmission, although it should be integrated with a broader hygiene educationprogramme dealing a variety of transmission routes.
Selection of reference pathogens and assumptions madeThe scenarios outlined above relate to two very different aspects to poor water supply withinhouseholds. To a certain extent, the measures put in place to control risks within piped distributionsystems should also be adequate to deal with many of the problems related to poor in-buildingplumbing and storage. However, a few selected aspects are included within this section because oftheir particular importance. The rest of the section focuses directly on the safe handling of waterand therefore may have greatest relevance to situations where the water supply is provided througha communal level of service.
Within-building storageFor in-building plumbing, two principal areas of concern are noted for which reference pathogensshould be selected. The first is regrowth within storage tanks and plumbing. As the principal riskwill be relate to Legionella pneumophila this is taken as a key reference pathogen. The second areaof concern is ingress into the storage or pipe work. The principal reference pathogen for this case istaken as being E.coli 0157. The control of all risks related to ingress are likely to be effective for alltypes of pathogen as they relate primarily to good sanitary integrity of the system as it can beexpected that any residual disinfectant will disappear rapidly.
The hazard assessment would clearly need to look for likely sources of faeces within the buildingand is likely to primarily look at whether there is potential access into the storage tank for rodentsand birds. Additional hazard factors to be considered will be the location of the tank and likelytemperature and the materials used for storage. Location close to roofs may increase hazards asaccess for rodents and birds may be greater and may lead to increasing temperatures. Metal tanksmay more readily support colonisation and exert a greater chlorine demand and may be likely toheat more quickly in hot weather than plastic tanks.
47
Household handling and storage when communal sources of water are usedWith respect to the handling and storage of water when the source is communal, the principalreference pathogen of concern is E.coli 0157. Whilst the recontamination by viruses and protozoamay occur, most of the basic measures to prevent contamination from these organisms do notsignificantly vary from those associated with bacterial pathogens. The only major difference willcome when in-house water treatment processes are used, for which drinking water qualitymanagement plans are defined separately. Actual health risks from viruses and cysts in drinkingwater may in any case be lower in situations where communal source provision predominates. Thisis because childhood exposure to viruses is likely to occur from other means and because cystexposure may be likely through direct human-animal contact. It is uncertain to what extent regrowthwill be a problem, but certainly could occur if cleaning was not adequately performed.
The hazards relate to the quality of source water (which therefore should be dealt with under theappropriate hazard assessment by source type) and potential subsequent contamination. Anadditional hazard is the presence of animals within the home. The most important hazard willalmost certainly be from contaminated hands and therefore wherever non-piped water storage ispractised it is safe to assume that hazards always exist.
IWRM and regulatory issues
Issue Justification/explanation (includes cross-referencing to support texts for checkingin finalisation
Appropriate actions
Regulations and codes of practice fordesign & construction of within-building storage of piped systems
Regulations and codes of practice willensure enforceable standards of design andconstruction are in place to promoteimproved within-building water supplies
Set up plumbing codes ofpracticeDesign and constructioncriteria outlinedLicensing of designengineers and plumbers
Users committee within largebuildings and complaints procedureoutlined
Users committees may provide a moreeffective mechanism for complaints and toenforce compliance with regulations.A complaints procedure will enableresidents to initiate actions against sub-standard work.
Establish user or residentscommittee with legalmandate.Establish complaintsprocedure
Reduce within-building storage Reducing within-building storage of waterwill reduce the risks of contamination. Theuse of direct supply mains should bepromoted as far as possible
Increase numbers ofdirect mains connections.
Where water is collected from acommunal source, promotehousehold water treatment
It is unlikely to be possible to preventcontamination solely through betterhandling, therefore household watertreatment may be more cost-effective inreducing health risks
Identify major microbialhazards and identifyacceptable treatmentprocesses. Establish linkswith private sector to selltreatment products.
Understand water collection patterns It is important to understand which sourcesof water used and for what purposes. Ifwater from different sources are used fordifferent purposes, separation of water maybe essential.
Water usage studies.
Increase level of service provisionand quality of service to reducestorage requirement
Where water sources are beyond the home,storage of household water may become anincreasing priority. Equally poor reliabilitymay lead to increased storage requirement.
Create incentives topromote uptake of moreconnections at higherservice level. Attempts toimprove reliability ofsupply.
48
Design issuesThere is usually significant scope for improved designs of within-building storage tanks. Improvedstorage containers are available for use when water is collected from a communal source by hand,but uptake may be influenced by a number of factors.
Design issue Justification/explanation (includes cross-referencing to supporttexts for checking in finalisation)
Where water is piped into the home,all residences should have at least onetap direct to the main supply
Provided the water supplier adheres to a water quality management planfor production and distribution of water, the water in main supplyshould be of good quality and within-building contamination reduced.
Codes of practice for within-buildingplumbing repairs
Codes of practice for hygiene when undertaking repairs are importantmeasures to prevent contamination during repair work. These should beenforceable through regulations and be subject to periodic assessment.
Within building storage tanks shouldbe covered
Tanks that are not covered are open to direct contamination fromrodents and birds. Evidence from a number of outbreaks suggests thatthis is a major cause of contamination. Inspection covers on tanksshould be properly secured.
Tanks should have drain valve andsluice valves
It should be possible to fully drain the tank to allow more effectivecleaning. It must also be possible to isolate the tank during cleaning andrepairs to prevent contamination being spread throughout the system.
Separate hot and cold water pipes The close proximity of hot and cold supply pipes has been linked toincreasing survival and regrowth of pathogens within water supplysystems as temperatures increase. Lagging of cold pipes maysignificantly reduce this potential.
Prevent back-flow from householdconnections and within buildingtanks.
Back-flow from tanks into the wider supply should be avoided toprevent widespread contamination. Back-flow preventers shouldtherefore be placed on all mains connections to large buildings. Back-flow potential may also be desirable within buildings to prevent thepotential for contamination from one user affecting the whole building.
System of water withdrawal fromhousehold container should behygienic
Unhygienic systems of water withdrawal may allow users hands tocome into direct contact with water, thus potentially leading tocontamination. By preference a tap should be used, but a hygienicallystored scoop can also be used
Household container should permitthorough cleaning
It should be possible to thoroughly clean the inside of the container.This may require scrubbing or disinfection.
Appropriate materials used forhousehold container
The choice of container material is essential. Clay pots are undesirableas they more readily support microbiological communities and usuallyrequire water to be scooped. Plastic materials tend to be less readilycolonised.
Hygiene education A hygiene education programme should be developed to promote safewater handling. This should cover aspects such as container type,cleaning of household water containers, safe withdrawal of water andpersonal hygiene. Participatory approaches are often preferred as theyencourage experiential learning.
Drinking water stored in a separatecontainer to other household water
This is of particular importance where more than one source of water isused and where particular sources are used only for particular purposes.Keeping drinking water in a separate container will help reduce the riskof contamination from water from other sources that are of lowerquality and used for non-drinking purposes.
Household storage container shouldbe stored off the ground and awayfrom reach of animals
When storage containers are located at floor level they will be morevulnerable to direct contamination from animals. Keeping watercarefully stored away from access to animals will greatly reducecontamination risks.
Storage container should be covered Open containers will be more likely to become contaminated as faecalmatter is more easily introduced into the water by a variety of routes.Direct contamination by rodents and other animals and birds is likely
Promotion of use of protected/treatedwater sources
Promoting the use of sources that are protected and/or treated and whichhave some form of water quality monitoring may be an effectivemechanism to reduce contamination of drinking-water.
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Household disinfectionHousehold disinfection has been used in a number of countries and proved effective in reducingrisks of epidemics and in reducing endemic diarrhoeal disease burdens. Chemical disinfectionmethods include the use of chlorine, iodine or mixed oxidants. This are generally found in eithertablet or liquid form. Physical disinfection includes boiling of water, UV radiation and low-costsolar disinfection techniques that work through a mixture of inactivation through temperature andexposure to UV radiation. Good evidence of efficacy is available for all these approaches, both interms of epidemiological evidence and in pathogen inactivation rates during operational testing.
The use of household disinfection has until recently received far less attention that it deserves.Some studies have suggested that household treatment of water would have limited impact onhealth where environmental sanitation or hygiene remained poor (see for instance, Vanderslice andBriscoe, 1993; Moe et al, 1991). However, increasing evidence from a number of initiativessuggests that this is not the case and significant reductions in diarrhoeal disease have been noted(see background document for details).
Heat induced inactivation is very effective for bacteria and cysts and a rolling boil (>95oC) willinactivate all pathogens. Inactivation of all types of pathogen also occurs at lower temperatures,with viruses being most heat resistant, followed by cysts and bacteria. Of the chemicaldisinfectants, chlorine is highly effective against bacteria and viruses, but far less so againstprotozoa. It is unlikely that chlorination would be recommended alone for removingCryptosporidium spp. cysts.
Iodine and the mixed oxidants both show greater effectiveness in cyst inactivation. However, as thelong-term use of iodine not be acceptable to most users, control of protozoan pathogens may bemore effective through filtration prior to disinfection. Polyiodide resins have proved effectivedisinfectants and release very little residual disinfectant as inactivation occurs on contact withbacteria. However, filtration prior to disinfection is usually essential in order to remove suspendedsolids from influent water. Commercial units have been produced that incorporate reverse osmosisand iodine resins and prototype units for ceramic filter/resin units are also available.
Solar disinfection has attracted increasing attention as a low-cost approach to producing water ofvery good microbiological quality. Low-cost solar disinfection systems have also been showncapable of reducing Cryptosporidium spp. and other pathogens in water, although this is likely to beprimarily be a function of increasing temperature. Many of these techniques operate on a combinedaction of heat inactivation and UV disinfection. UV filters are also commercially available andknown to be effective. These would tend to be larger-scale units and likely to be used for largebuildings rather than individual households given the expense.
Selection of reference pathogens and assumptions madeThe use of household disinfection is always promoted because of concerns over the quality of thewater at sources or because of concerns regarding contamination during transport, handling andstorage.
The principal reference pathogens are Hepatitis A virus and E.coli 0157 to ensure that efficacy wasassured. This may be expanded to include Cryptosporidium parvum when the disinfectant used isexpected to inactivate cysts during practical operation. As household water treatment imply hazardsare available, there is little point in undertaking hazard assessments other than those related to risksof source contamination or recontamination during handling.
Colonisation of certain types of household treatment systems have been noted, but would not beexpected to represent a major problem for systems that are only for disinfection as colonisationappears most marked in filter units. Furthermore, where disinfection would be expected to directly
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control re-growth and therefore it would not be expected that the use of Legionella pnuemophilawould be necessary.
It is important to note that when manufacturers or developers of household disinfection units arepromoting their products that evidence is provided on pathogen inactivation and not simply onindicator bacteria reductions. This is essential as many of these units can be expected to be highlyefficient with regard to coliform bacteria, but may have far less effectiveness against pathogens. Itis also essential that data is presented on the basis of challenge experiments involving both batchand continuos run experiments. The latter should be designed to mimic real operating conditionsand following the recommended cleaning procedures and frequencies. Failure to provide this typeof data should suggest that licensing for widespread use is not justified, although this data could becollected through pilot field trials in the country.
IWRM and regulatory issues
Issue Justification/explanation (includes cross-referencing to support texts for checkingin finalisation
Appropriate actions
Environmental technologyverification protocols should existthat allow for proper evaluation of alltreatment products
Household disinfection technologies shouldbe evaluated properly to ensure efficacy.This would usually require certificationfrom country of origin and assessment tomeet national criteria
Technology verificationprotocols should bedeveloped.
Regulations and licensing systemestablished to ensure standardsdefined
Regulations should govern manufacturersand wholesalers of household disinfectionproducts. These should covermanufacturing specifications to meetdefined water quality targets. It may alsocover advertising controls.
Establish registration andlicensing procedure andlead agency. Regulationsand performancestandards should beclearly outlined andcompliance a requirementfor licences.
All licensed household disinfectionsystems should provide data onpathogen inactivation based oncontinuous run and batch experiments
Pathogen inactivation should be proven inorder to support claims about effectiveness.Data on indicator bacteria alone should notbe accepted. Batch and continuous runchallenge tests should be presented. Thelatter is particularly important and shouldreflect recommended operating procedures.
Establish scientific reviewbody. Establish procedurefor data submission andreview. Set up data bankfor storing data.
Legal requirement formanufacturers/retailers to makeinformation available to users aboutsource water requirement, pre-treatment needs, maintenance needsand operating conditions
A lack of information about source waterrequirements, pre-treatment requirements,maintenance schedules and operatingconditions may lead to confusion anddeteriorating performance and ultimately toincreasing health risks
Labelling of products alegal requirement.Establish penalties fornon-compliance.Information to beincluded on labelsspecified by licensingauthority.
Use of household treatment does notpreclude investment in public watersupply
Household disinfection may well meet shortto medium terms needs. However, thepresence of effective householdtechnologies should not be result in reducedinvestment in public water supply
Continued investment inwater supplyinfrastructure.
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Design issues
Design issue Justification/explanation (includes cross-referencing to supporttexts for checking in finalisation)
Operating and maintenance,specifying any water quality or otherenvironmental control on efficiencyinformation provided clearly
Many household disinfection systems fail because operation andmaintenance requirements are not well understood and allowbreakthrough of pathogens
Design ensures contact adequate Ctvalue for inactivation
The inactivation of pathogens by disinfection is a function of theconcentration of disinfectant and time for which pathogens are exposedto the concentration.
Systems do not deliver harmful dosesof disinfectants
Where chemical disinfectants are used, doses provided should be withinsafe limits based on national standards or WHO Guidelines. Dosecontrol should be proven for all recommended operating conditions.
Design dose should be maintainedthroughout working life
Doses of some forms of chemical disinfectants (e.g. some resins) mayvary with time and dose delivered decreases with time. This may lead toincreasing risks of pathogen survival.
Systems should not allowcolonisation by bacteria
Only relevant to combinations systems with filtration/substrate. In thesecases, re-colonisation must be controlled with accepted life span.
Consumables (where needed) shouldbe readily available and affordable
If consumables are needed for ongoing operation they should be readilyavailable and affordable to promote widespread uptake.
Household filtration systemsHousehold filtration systems encompass a wide variety of technologies from sophisticated systemsusing reverse osmosis or micro-filtration, through less complex systems such as activated carboncartridges, ceramic filters and combination units with disinfectants included, to very simpletechniques using filtration based on sand or other granular media. The more complex systems tendto be those found in commercial units and which may be expensive to purchase. These may be pointof entry units (i.e. plumbed into the piped water supply as it enters the home) or much smaller pointof use systems. The very simple technologies are more typical of point of use units used at ahousehold levels and less expensive to construct, although not necessarily lower maintenance.
Filtration devices remove particulate matter from water and as a result may lead to reductions inpathogen loads. Direct pathogen removal will primarily be a function of the pore size, althoughsome adsorption onto the filter media may also occur. It is unlikely that either of these processeswill be fully effective for viruses or bacteria, although in most fine filters cyst removal should beeffective.
Particular attention should be paid to the development of cracks the filter media as this may allowrapid short-circuiting of the filter and increasing risks of pathogen breakthrough. Some ceramicfilters are impregnated with silver which it is claimed will function as a disinfectant. There is littleevidence of long-term bactericidal effect of silver and studies suggest that the bacteriostaticproperties may be limited as silver tolerant bacteria can colonise filters. It is possible that that thelimitations of the silver impregnation occur because whilst initial concentrations released are high,they rapidly decline to levels too low to be effective.
More expensive and very fine filters, for instance based on membrane filtration are likely to removemore pathogens. Micro-filtration will be effective against cysts, but would be not be effectiveagainst bacteria and viruses, although removal of particulate matter may reduce concentrations to acertain degree. Reverse osmosis would be expected to remove virtually all pathogens, but cloggingmay be problem. More widely available commercial units using ceramic or carbon filters willremove cysts and some bacteria and viruses. However, breakthrough by of viral or bacterialpathogens is common. Both types of filter may also be prone to colonisation, including byLegionella pneumophila. Water from such filters should normally be disinfected prior toconsumption.
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Simple filtration units are known to be effective for removing larger pathogens and may be useful inguinea worm eradication programmes. Their efficacy in bacterial, viral and protozoan pathogenremoval is less certain. There are few available studies that evaluate the effectiveness of many ofthe much simpler filtration units in pathogen removal, largely because their application has been invery poor and often remote communities. The limited evidence available provides information onreductions in turbidity and indicator bacteria. These show that thermotolerant coliforms are rarelyconsistently absent, suggesting limited ability to remove pathogens.
Selection of reference pathogens and assumptions madeAs filtration of water within the home may be carried out either because the water supply is of poorquality or because of concerns over chemical quality, the use of all four key reference pathogenscould be justified to a certain extent. However, this may not be case in all circumstances and thereference pathogens selected may be somewhat dependent on the type of technology and the socio-economic conditions.All filters would be expected to be effective at least against cysts and therefore Cryptosporidiumparvum should be considered a reference pathogen against which performance is measured, even insituations where alternative routes of transmission may be more important. For simple granularfilters and for ceramic candle filters and carbon filters without disinfectant impregnation this is willbe the only valid reference pathogen. Disinfection of the water after filtration should be alwaysrecommended (unless specific evidence can be provided on bacterial and viral inactivation). Wherethe filter unit includes a disinfectant or uses reverse osmosis, then Hepatitis A, E.coli 0157 andLegionella pnuemophila should be considered as reference pathogens.
As the use of household filtration implies that source waters are contaminated, hazard assessmentsother than those related to the source are not necessary.
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IWRM and regulatory issuesThese are effectively the same as for household disinfection, but are repeated here for completeness.
Issue Justification/explanation (includes cross-referencing to support texts for checkingin finalisation
Appropriate actions
Environmental technologyverification protocols should existthat allow for proper evaluation of alltreatment products
Household filtration technologies should beevaluated properly to ensure efficacy. Thiswould usually require certification fromcountry of origin and assessment to meetnational criteria
Technology verificationprotocols should bedeveloped.
Regulations and licensing systemestablished to ensure standardsdefined
Regulations should govern manufacturersand wholesalers of household disinfectionproducts. These should covermanufacturing specifications to meetdefined water quality targets. It may alsocover advertising controls.
Establish registration andlicensing procedure andlead agency. Regulationsand performancestandards should beclearly outlined andcompliance a requirementfor licences.
All licensed household filtration unitsshould provide data on pathogeninactivation based on continuous runand batch experiments
Pathogen inactivation should be proven inorder to support claims about effectiveness.Data on indicator bacteria alone should notbe accepted. Batch and continuous runchallenge tests should be presented. Thelatter is particularly important and shouldreflect recommended operating procedures.
Establish scientific reviewbody. Establish procedurefor data submission andreview. Set up data bankfor storing data.
Legal requirement formanufacturers/retailers to makeinformation available to users aboutsource water requirement, pre-treatment needs, maintenance needsand operating conditions
A lack of information about source waterrequirements, pre-treatment requirements,maintenance schedules and operatingconditions may lead to confusion anddeteriorating performance and ultimately toincreasing health risks
Labelling of products alegal requirement.Establish penalties fornon-compliance.Information to beincluded on labelsspecified by licensingauthority.
Use of household treatment does notpreclude investment in public watersupply
Household filtration may well meet short tomedium terms needs. However, thepresence of effective householdtechnologies should not be result in reducedinvestment in public water supply
Continued investment inwater supplyinfrastructure.
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Design issues
Design issue Justification/explanation (includes cross-referencing to supporttexts for checking in finalisation)
Operating and maintenanceinformation provided clearly
It is essential that the conditions under which the filtration process willbe effective and the maintenance requirements should be clearlyspecified on the unit.
Materials specification Materials allowable for use in filters should be specified. This may havedifferent categories of filter types. Aspects such as pore size and mediatype should be specified.
Cleaning procedure and guidance onmedia or cartridge replacement
This should simple and easy to follow. Manufacturers recommendationsshould err on the side of caution, as most users will probably not followrecommendations exactly
Filtration rate adequate The filtration rate that is acceptable is dependent in part on what thefilter is designed to achieve: whether particulate matter removal orpathogen reduction. However, the filter should be assessed against theperformance criteria claimed by the manufacturer.
Pore size is uniform Poor performance of many filters arises through variations in pore sizeand the development of short-circuit pathways. This is a particularproblem for quality control in ceramic filters
Assessment of efficiency ofpathogens/particulate removal
Assessment data should be made available to support evidence ofremoval so that information can be provided to users on performanceexpected. If filter does not produce water of acceptable levels,additional treatment steps required should be outlined.
