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Drinking Water Chlorination
2 DrinkingWaterChlorination•WorldChlorineCouncilpositionpaper2008
The use of chlorine to protect drinking water
is one of the greatest public health advances in history. Chlorine
destroys disease-causing organisms in water and is the most
commonly-used disinfectant in all regions of the world.
The World Chlorine Council® (WCC) has published this paper to briefly
address key issues related to drinking water chlorination:
• Chlorine’scriticalroleinprovidingsafedrinkingwateraround
the globe;
• Potentialhealthandenvironmentaleffectsofchlorineand
disinfection byproducts in treated drinking water; and
• Considerationsforselectingdisinfectionmethods.
TheWorldChlorineCouncil(WCC)isaglobalnetworkrepresentingthechlorineandchlorinatedproducts
industries.Formedin1993,theWCCcurrentlyrepresentsover23national/regionalassociationsinover
27countriesaccountingforover80percentofglobalchlorineproduction.TheWCCworksto improve
awarenessof thebenefitsofchlorinechemistry; further thepracticeandunderstandingof responsible
stewardship;andanticipateandrespondtorelevanthealth,environmentalandpublicpolicyissues.
DrinkingWaterChlorination•WorldChlorineCouncilpositionpaper2008 3
Helping to provide safe drinking water around the globe
Chlorine is effective, affordable, and widely available for disinfection
Chlorineisusedtodestroydisease-causingorganismsinwater,anessentialstepindeliveringsafe
drinkingwaterandprotectingpublichealth.Chlorineisbyfarthemostcommonlyuseddisinfectant
inallregionsoftheworld.Wherewidelyadopted,chlorinehashelpedtovirtuallyeliminatewater-
bornediseasessuchascholera,typhoidanddysentery.Chlorinealsoeliminatesslimebacteria,molds
andalgaethatcommonlygrowinwatersupplyreservoirs,onthewallsofwatermainsandinstorage
tanks.Only chlorine-baseddisinfectants leaveabeneficial“residual” level that remains in treated
water,helpingtoprotectitduringdistributionandstorage.
Chlorine isaversatileand low-costdisinfectantappropriate foranysizewater system,whether it
servesaremoteruralvillageoralargemoderncity.Wherepipedwatersuppliesarenotavailable,
chlorinecanalsobeused for treatingwater in individualhouseholds.Specially-packagedchlorine
bleachcandisinfecthouseholdwaterforlessthanUS$4/yearperfamily.
In addition, chlorine is critically needed for emergency relief efforts. In responding to the 2004
tsunamidisasterinSouthAsia,theWorldHealthOrganization(WHO)reported,
“Chlorine is most widely and easily used, and the most affordable of the drinking water
disinfectants. It is also highly effective against nearly all waterborne pathogens.”
Water and sanitation: A global health crisis
Morethanonebillionpeopledonothaveaccesstoasafewatersupplywithin1kmoftheirhomes,
relyinginsteadonunprotectedlakes,streamsorshallowwellstomeethouseholdneeds.Evenwhere
relativelycleanwaterisavailableatacommunitysource,itcaneasilybecontaminatedasit iscol-
lected,carriedandstoredinthehome.WHOestimatesthatmorethan4,000peopledieeachday
fromdiarrhoealdiseasesresultingfromunsafewaterandlackofsanitation.Ninetypercentarechil-
drenundertheageoffivewholiveindevelopingcountries.
Safe water: Essential for sustainable development
TheUnitedNationshasrecognizedthecriticallinkbetweensafewaterandsustainabledevelopment.
Accesstosafewaternotonlyreducesdisease,butalsoprovidesarangeofeconomicbenefitsfora
community.
Atthe2002WorldSummitonSustainableDevelopment,theUnitedNationsreaffirmeditscommit-
menttoreducebyone-halftheproportionofpeoplewithoutaccesstosafewaterby2015.Meeting
thisgoalwillrequiresustained,coordinatedactionandenormousinvestmentseachyear.WHOhas
concludedthatglobalinvestmentstoimproveaccesstosafewateraccesswillyielddirectandindirect
benefitsthatfarexceedtheassociatedcosts.
4 DrinkingWaterChlorination•WorldChlorineCouncilpositionpaper2008
Chlorine and disinfection byproducts in drinking water do not pose significant health or environmental risks
Chlorine in drinking water is safe for consumption
Thesmallamountofchlorinetypicallyusedtodisinfectwaterdoesnotposeriskstohumanhealth.The
WorldHealthOrganization(WHO)hasestablishedaguidelinevalueof5mg/Lforchlorineindrinking
water,meaningthatsuchconcentrationsareconsideredacceptableforlifelonghumanconsumption.
Furthermore,WHOconcludesthatthisvalueis“conservative,”asnoadverseeffectsfromchlorinein
drinkingwaterwereobservedinstudiesreviewedbyWHO.
DBPs should be controlled, but disinfection must never be compromised
Anothersafetyconsiderationfortreateddrinkingwaterisdisinfectionbyproducts(DBPs),chemical
compoundsformedunintentionallywhenchlorineandotherdisinfectantsreactwithcertainorgan-
icmatter inwater.Alldisinfectants formDBPs,althoughmuchmore isknownaboutchlorination
byproducts than isknownaboutthebyproductsofotherdisinfectants.Forexample, toxicological
studiessuggestthatsometrihalomethanes(THMs)arecarcinogenictolaboratoryanimals,butonly
atlevelsmanythousandsoftimesgreaterthanthosefoundindrinkingwater.Researchhasshown
thatchloroform(themaintypeofTHM)isunlikelytocausecanceratextremelylowlevelsfoundin
drinkingwater.WhilethepotentialhealthrisksfromDBPsaresmallanduncertain,highlevelsofthese
chemicalsarecertainlyundesirable.WHOhasestablishedguidelinevaluesforseveralDBPs,including
trihalomethanes.
Guideline values for chlorine and trihalomethanes
WHO Guidelines for drinking water quality (2004)
Chlorine below5milligramsperliter(mg/L)*
Bromodichloromethane below0.06mg/L
Bromoform below0.10mg/L
Chloroform below0.20mg/L
Dibromochloromethane below0.10mg/L
* Foreffectivedisinfection,thereshouldbearesidualconcentrationoffreechlorineof0.5mg/L
afteratleast30mincontacttimeatpH<8.0
DrinkingWaterChlorination•WorldChlorineCouncilpositionpaper2008 5
DBPformationcanbereducedthroughcost-effectivemethods,particularlybyreducingtheamount
ofnaturalorganicmaterialinwater(throughfiltrationorothermeans)priortodisinfection.WCCsup-
portsadoptionofthesemethodswheneverpossible.However,asWHOstronglycautions:
“The health risks from these byproducts at the levels at which they occur in drinking water
are extremely small in comparison with the risks associated with inadequate disinfection.
Thus, it is important that disinfection not be compromised in attempting to control such
byproducts.”
AstarkexampleoftheimportanceofwaterdisinfectionisthecholeraepidemicthatbeganinPeruin
1991,andspreadto19LatinAmericancountries.Inadequatedisinfectionofmunicipalwatersupplies
wasamajorfactorcontributingtothespreadoftheepidemicthatcausedmorethanonemillionill-
nessesand12,000deaths.Duringtheoutbreak,officialswiththePanAmericanHealthOrganization
reportedthatconcernsaboutpotentialhealthrisksfromdisinfectionbyproducts ledmunicipalities
andcommunitiesintheregiontoabandonchlorination.Oneofficiallaterwrote,“Ratherthanbeing
abatedby increaseuseofchlorination,thewaterbornetransmissionofcholerawasactuallyaided
becauseofworriesaboutchlorinationbyproducts.”
Chlorination does not harm aquatic environments
Chlorinateddrinkingwater is unlikely to beharmfulwhendischarged into aquatic environments.
AnextensiveriskassessmentconductedunderEuropeanUnionguidelinesexaminedpotentialharm
fromvariousprocessestomakedrinkingwaterusingsodiumhypochlorite.Thisassessmentfoundno
significantenvironmentalrisksfromchlorineorbyproductsformedduringdrinkingwaterchlorina-
tion.TheDBPsformedindrinkingwaterdependonthenatureandquantityoforganicmatterpresent
aswellasonthedisinfectantandothertreatmentsused.Indrinkingwatertheprincipalbyproducts
aretrihalomethanes(THMs;mainlychloroform)andhaloaceticacids(HAAs),withsmalleramounts
ofotherbyproducts.Direct‘wholeeffluent’experimentsrepresentingvarioususes,includingdrink-
ingwater, have shown that no significant amounts of persistent and potentially bioaccumulative
substancesareformed.ToxicitytestsonthesemixturesdemonstratedthatthepresenceofDBPsdid
notincreasethetoxicity.
Amajorconcernfromthepastwastheformationofsomehighly-chlorinated,high-hazardmolecules,
suchasdioxins, resultingfromchlorineused inpaperpulpbleaching.However,dioxinswereonly
formedfrom‘activechlorine’underspecificconditions:acidpHandinthepresenceofcertainphe-
nolssuchasthoseabundantinthelignincomponentofwood.Thereisnosignificantformationof
dioxinsorotherhigh-hazardmoleculesatneutraloralkalinepH.Allcurrentusesof‘activechlorine’
formicrobialcontrolandcleaningtakeplaceatalkalineorneutralpH.
6 DrinkingWaterChlorination•WorldChlorineCouncilpositionpaper2008
Disinfection technologies must be effective, affordable and appropriate for local conditions
Various technologies are available
Chlorinationisthemostwidelyuseddisinfectant,bothincentralizedwaterdistributionsystemsand
for point-of use treatment in individual households. Its effectiveness against awide spectrumof
disease-causingorganisms,relativelylowcostandhighreliabilitycontributetoitspopularity.
Chlorineisappliedtowatereitheraselementalchlorine(chlorinegas),orthroughtheuseofchlorin-
atingchemicalssuchascalciumhypochlorite(tabletsorgranules)orsolutionsofsodiumhypochlorite
(liquidbleach).While varying in formandconcentration,eachproduces“free chlorine” toattack
germsinwater.Theleveloffreechlorinecanbeeasilymonitored,providinganimportantmeasureof
waterquality.A“residual”levelofchlorinehelpsprotecttreatedwatertreatedwaterinthedistribu-
tionsystem,particularlyimportantforolderwatersystems.
Anumberofalternativemethodsareavailablefordrinkingwaterdisinfection.Theseinclude:ozone,
apowerfuldisinfectingagentgeneratedbypassingoxygenordryairthroughasystemofhighvolt-
ageelectrodes;chlorinedioxide,apowerfulchemicalthatcontainschlorinemolecules,butdisinfects
through a differentmechanism than free chlorine; and ultraviolet (UV) radiation, a non-chemical
methodtodisinfectwaterusinglightgeneratedbyspeciallamps.Inaddition,someharmfulmicro-
organismscanberemovedfromwaterthoughfiltrationorotherphysicalmeans.Filtrationmethods
rangefromsimplesandfiltersforhouseholdtreatment,toreverseosmosissystemsinstate-of-the-art
treatmentplants.
Eachdisinfectiontechnologyhasuniquestrengthsandlimitations.Nosingledisinfectionmethodis
rightforallcircumstances,andinfact,amulti-stepprocessmaybeappropriatetomeetoveralltreat-
mentgoals.
DrinkingWaterChlorination•WorldChlorineCouncilpositionpaper2008 7
Considerations for selecting disinfection methods
Efficacy against pathogens—Controllingmicrobialcontaminationmustalways
begivenprimaryimportance.Whilechlorineiseffectiveagainstmostpathogens,
additional treatment stepsmay be neededwhere resistant organisms such as
Cryptosporidium or Giardiaareaconcern.
Laws and regulations—Treatmentprocessesandfinaldrinkingwaterqualitymust
meetlocalstandards.
Source water quality—Thecharacteristicsoflocalsourcewater,suchasturbidity
andorganicload,willimpactdisinfectionrequirements.
Residual protection—Onlychlorine-basedproductsprovidea“residual”levelof
disinfectantthatremainsinwatertopreventmicrobialre-growthandhelppro-
tecttreatedwaterduringdistributionandstorage.Therefore,nootherdisinfec-
tionmethodbyitselfcanprotectwaterallthewaytothetap.
Local capacity—Sufficient resources, suppliesandtrainingmustbeavailable to
maintainserviceaftertreatmenttechnologiesareadopted.
Safety—Alldisinfectionchemicalsrequireproperstorageandhandlingpractices.
Safetyguidelinesareavailablefromnationalandregionalchlorineassociations.
Consumer expectations—Educationaleffortsmayhelplocalcommunitiesunder-
stand the need for water disinfection, and ensure acceptance of treatment
methods.
Affordability—Waterserviceand/orhometreatmentproductsmustbeaffordable
toconsumers.
www.worldchlorine.orginfo@worldchlorine.org
WCCmembers
Producer AssociationsAsociacionNacionaldelaIndustriaQuimica(Mexico)
www.aniq.org.mx/
CanadianChlorineChemistryCouncil
www.cfour.org
ChlorineChemistryDivisionoftheAmericanChemistry
Council
www.americanchemistry.com/chlorine
ChlorineInstitute
www.cl2.com
Clorosur
www.clorosur.org
EuroChlor
www.eurochlor.org
IndianChemicalManufacturersAssociation
JapanSodaIndustryAssociation
www.jsia.gr.jp
KoreaChlor-AlkaliAssociation
PlasticsandChemicalsIndustriesAssociationofAustralia
www.pacia.org.au
Taiwan(China)Acid&AlkaliIndustryAssociation
Product Sector AssociationsAsia-PacificVinylNetwork
EuropeanCouncilofVinylManufacturers
www.ecvm.org
HalogenatedSolventsIndustryAlliance
www.hsia.org
VinylCouncilofAustralia
www.vinyl.org.au
VinylCouncilofCanada
www.plastics.ca/vinyl
VinylEnvironmentalCouncil(Japan)
www.vec.gr.jp
VinylInstitute
www.vinylinfo.org
Corresponding AssociationsRusChlor,theRussianchlor-alkaliassociation
ChinaChlor-AlkaliIndustryAssociation[pending]