WATER SUPPLY AND SANITARY ENGINEERINGMethods of layout of distribution pipes:Following are the main four methods of laying distribution pipes:(1) Dead-end method(2) Grid-iron method(3) Circular method(4) Radial method.It may however be noted that each system has its own merits and no locality strictly adopts only one of these methods. The necessary combinations of the above methods are usually made to suit the local conditions of the area.Dead-end method:This is also known as tree system of layout and it consists of one supply main from which sub-main are taken. The sub-mains again divide into several branch lines from which service connections are givcn to the consumers. FigT 14-6 shows the sketch of a typical dead-end or tree system of layout of distribution pipes. The diameter of mains,sub-mains and branches are suitably designed.

Dead-end method of layout

Advantages:(i) It is possible to work out accurately the discharge and pressure at any point in the distribution system. The design calculations arc simple and easy.

(ii)The cut-off valves required in this system of layout are comparatively less in number .(iii)The diameters of mains are to be designed for the population likely to be served by them only.This fact may make the system cheap and economical.(iv)Laying of water pipes is simple.Disadvantages(i)During repairs,large pordon of distribution area is affected and it results into great inconvenience to the consumers of that area.(ii)There are many dead-ends in this system. The pipes terminate at the dead-ends and hence, there is no free circulation of water. There are chances for water to be polluted due to stagnation and it may endanger the public life. For this purpose, scour valves arc provided at dead-ends and stale water from dead-ends is removed periodically by the operation of these

valves. This measure proves to be costly as treated water is thrown to waste and it also requires careful attendance and operation of the scour valves.(iii)The water available for fire fighting will be limited in.quantity as the discharge, from mains is also limited. This may prove to be serious in some cases.

Use:The dead end system of layout is adopted in localities which arc expanding irregularly. The water pipes are laid at random.Without any planning of future roads.(2) Grid-iron method:This is also known at interlaced system or reticulation system. The mains, sub-mains and branches are interconnected with each other as shown in fig 14-7.

In case of repairs, a very small portion of the distribution area will be affected. There is free circulation of water and hence, it is not liable for pollution due to stagnation. iii) The water is delivered at every point of distribution system with minimum loss of head. iv)When a fire occurs, plenty of water is available for fire fighting purpose and by manipulating the cut-off valves, whole supply of water may be concentrated for this purpose.

Disadvantages(i)The cost of laying water pipes is more.(ii)The grid-iron system of layout requires longer lengths of pipes(iii)The procedure for calculating sizes of pipes, and for working out pressures at various points in the distribution system is laborius,complicated and difficult.(iv)The valves required in this system are more in number and in fact, four valves are to be installed at every cross junction.

Use:The grid-iron system of layout is more suitable for towns having well-plane, roads and streets. However, the principle of grid-iron system can be applied. to dead-end system of layout by removing dead-ends as shown by dotted line in fig. 14-6.

(3) Circular method:This is also known as ring system and a ring of mains is formed around the distribution area as shown in fig. 14-8.This system possesses advantages and disadvantages as those of grid-iron system. The distribution area is divided into rectangular or circular blocks and the water mains are laid on

the periphery of these blocks. The ring system of layout is most suitable for towns having well-planned roads and streets.

Circular method FIG. 14-8Radial method;This method .of layout is just the reverse of the ring method. In this system, the water is taken from the mains and pumped into the distribution reservoirs which are situated at centres of different zones as shown in fig. 14-9. The: water is then supplied through radially laid pipes. The radial method of layout gives quick service and calculations for design of sizes of pipes are simple. The radial method is most suitable for towns having roads laid out radially.

Wastage of water :A considerable amount of filtered water is wasted rather than invested mainly because of the following two reasons:(1)By carelessness of consumers (2)By leakage through pipe joints.In order to ascertain 'the amount of wastage of water, the waste water surveys are carried out. If wastage of water is brought down to the minimum possible extent, it results is increased supply of water to the consumers and it also helps in the reduction of cost of treated water.Waste water surveys: .To carry out waste water surveys, a certain area of the locality is isolated from the rest by proper manipulation of valves.The flow of water through pipes is then recorded and the results thus obtained are suitably analysed.If wastage of water is found to be excessive,the area is further

Business or trade purposes

Some trades such as dairies, hotels, laundries, motor garages, restaurants, stables, etc. require a large quantity of water. Such trades are to be maintained in hygienic conditions and sanitation of such places should be strictly Insisted. The number of such business centres will depend upon the population and for a moderate city, an average Value of about 15 to 25 litres per head per day may be taken as water requirement for this purpose.(5) Loss and waste:The quantity of water required under this category is sometimes termed as unaccounted requirement.It includes careless- use of water, leakage in mains, valves, other fittings, etc.,unauthorised water connections and waste due to other miscellaneous reasons. The quantity of water lost due to all these reasons is uncertain and cannot be effectively predicted. However, for the purpose of calculating the average rate of demand, it may be estimated to be about 30 to 40 per cent of per capita consumption.If the distribution of water is entirely through metres only and if the distribution system is well-maintained, it is possible to bring down the percentage of unaccounted water to the extent of about 10 to 15. Problem 2.Work out the role of demand of water for at average Indian city.Make your own assumptions,where necessary..Solution:Total requirement of water for various purposes is worked out separately as under;Purpose Litres/h cad/day(I) Domestic purposes:Drinking ...................................................................................... 2 Gooking........................................................................................ 5Bathing.......................................................................................... 35Washing hands, face, etc……………………………………………. 8Household sanitary purposes…………............................................ 50 Purpose Litres/head/dayCivic or public purposes:Road washing ...........................………………………………………5Sanitation purposes .....,.................................................................. 3Ornamental purposes... .................................................................... 1demand............................................................................................ 1Industrial purposes:Moderate factories............................................................................50Business or trade purposes:Dairies, hotels, etc............................................................................15Loss and waste :Assumed as....................................................................................... 75 Grand total... .250 For average Indian towns, per capita consumption of water per day varies from 150 to 300 litres. It is to be noted that there is a big gap between urban and rural water consumption per capita because of obvious reasons such as absence of industrial units,lack of commercial activities etc.It is estimated that the world’s average urban water consumption per capita is 150 litres per day or about 55 m3 per year and that the world's average rural water consumption per capita is only 50 litres per day or about 18m3 per year.Factors affecting rate of demand :There are various factors which influence the rate of demand of water. These factors art to be analysed carefully properly before arriving at the rate of demand for particular locality. Following are the factors affecting rate of demand:

Climatic conditions Cost of water Distribution pressure Habits of population Industries Policy of metering Quality of water Sewerage Size of city System of supply

We will now briefly discuss each factor.

(1)Climatic conditions :The requirement of water in summer is more than that in winter. So also is the case with hotter and cooler places. In extreme cold, people may keep water taps open to avoid freezing of pipes. This may result in increased rate of consumption. (2)Distribution pressure:The rate at which water is supplied to the consumers may also affect the rate of demand. The higher the cost, the lower will be the rate of demand and vice versa.(3) Distribution pressure:The consumption of water increases with the increase in the distribution pressure. This is due to increase in loss and waste of water at high pressure. For instance, an increase of pressure from 2 to 3 kg/cm2 may lead to an increase in consumption to the extent of about 25 to 30 per cent. .The designer therefore should only provide for distribution pressure which is necessary for rendering satisfactory service.

(4)Habits of population:For high-value premises, the consumption rate of water will be more due to better standard of living of persons. For middle-class premises, the consumption rate will be average •while in case of slum areas, it will be much lower. A single water tap may be serving several families in low-value areas.[5) Industries:The presence or absence of industries in a city may also affect its rate of demand. As there is no direct relation between the water requirement for industries and popular tion, it is necessary to calculate carefully present and future requirements of industries.(6) Policy of metering:The quantity of water supplied to a building is recorded by a water meter and the consumer is then charged accordingly. The installation of meters reduces the rate of consumption. But the fact of adopting policy of metering is a disputable oneas seen from the following arguments which are advanced for and against it.Arguments for policy of metering; (i) It becomes very easy to locate the points of leakage when meters are installed.(ii) The consumer is charged in proportion to the quantity of water which he uses.(iii) The reduction in consumption of water results in decrease in loads oh purification plants, pumps, sewers, etc(iv) Wastage of water is decreased.(v) The careful consumer pays less and the careless consumer pays more.

Arguments against policy of metering:

(i) There is loss of pressure due to installation of meters and it adds to the pumping cost.(ii) Use of water for gardens, fountains, etc. is greatly diminished. This decreases the beauty of the locality.(iii) The limited use of water may lead to unhygienic conditions and may cause epidemic.(iv) The policy of metering is expensive in the sense that cost is to be incurred to buy to install, to read and to maintain the meters.(v) It is suggested that amount spent after introducing-the policy of metering may well be spent in improvement of water supply scheme itself.In conclusion, it may be stated that engineers dealing with water supply schemes, recommend installation of water meters, when the following two conditions are existing:(a) Quantity of water that is available from the source is limited.(b) Total cost of water supply scheme is an important consideration.

(7) Quality of water:The improvement in quality of water may result in the increase of rate of consumption. The public using the improved water will consider it safe and may make various uses of the available water. On the other hand, if water has unpleasant taste or odour, the rate of consumption will come down.(8) Sewerage:The existence of sewerage system in a locality will lead to an increase in use of water for civic or public purposes. The people will also use more quantity of water for flushing sanitary units such as urinals and water closets.(9) Size of city :Generally, the smaller the city, the lower is the rate of demand. But the presence of a water-consuming industry in a small town may result in a higher-rate of demand, even if the town is small.(10) System of supply:The supply of water may be continuous or intermittent. In the former case, water is supplied for 24 hours and in the latter case, it is supplied for certain duration of day only. It is claimed that the intermittent supply system will reduce rate of demand. But sometimes, the results are proved to be disappointing, mainly for the following two reasons:(i) During non-supply period, the water taps are kept open and hence, when the supply starts, water flowing through open taps is unattended and this results in waste of water.(ii) There is a tendency of many people to throw away water stored previously during non-supply hours and to collect fresh water. This also results iii waste of water.Measurement of waterDuring the process of water supply scheme, it becomes necessary to measure the quantity of water for the following reasons:

Meaning of the term:The drainage of a locality is broadly divided into two categories — public and privateSewers are laid across public roads to serve the area on either side. Private plot holders construct the sewer line in their own land and its final point is then joined to the public sewer. Principles and procedures to be followed while constructing and laying sewer lines in private buildings are referred to by the general term house drainage. The main purpose of house drainage is to provide an efficient drainage-system. Importance of house drainage can understood by the fact that every locality develops its own bye-laws or regulations which are to be strictly followed before seeking a drainage connection to the public sewer line.Principles of house drainage:

For the proper design and construction of house drainage system, the following general principles are adopted:(1)It is advisable to lay sewers by the side of building rather than below the building(2)Drains should be laid straight between inspection chambers or manholes. All sharp beads and junctions should be avoided except through chambers or manholes.(3)The entire system should be properly ventilated from the starting point of disposal.(4)The house drain should be connected to the public sewer only if the level permits i.e. only when public sewer is deeper than the house drain. Otherwise, there will be reverse flow from public sewer to house drain.(5)the house drainage should contain enough number of traps at suitable points for efficient functioning of it.(6)the house drain should be disconnected from the public sewer by the provision of an intercepting trap so as not to allow foul gases from public sewer to enter the house drain.(7)joints of sewers should be watertight and should be properly tested before putting the drainage line in use.(8)lateral sewers should be laid at proper gradient so that they will develop self-cleansing velocity.(9)the layout of house drainage system should permit easy cleaning and removal of obstruction.(10)materials of sewer should comply with standard requirements.They should be non-absorbent and an earth cushioning should be provided to protect them from external loads.(11)possibilities of formation of air locks,siphonage, undue deposits,etc.should be properly studied and adequate remedies should be accommodated in design to avoid them(12)rain water from houses is collected from roofs and it is allowed to flow freely on the road surface for catch basins or inlets to convey it to the storm water drain.(13)the sewage formed should be conveyed as early as possible after its formation.(14)the size of lateral sewers should be such that they will not overflow at the time of maximum discharge.

Traps:Definition:A trap is a depressed or bent sanitary fitting which always remains full of water.it is technically termed to contain water seal which is measured as the vertical distance between crown and dip of a trap.

Function:Function of a trap in a drainage system is to prevent the passage of foul air or gases through it.But at the same time,it allows the sewage to flow through it. Thus, the installation of a trap avoids the nuisance which will be developed due to entry of bad smelling gases into the house.The effectiveness of trap naturally depends upon the depth of water seal. The greater the depth of water seal, the more effective is the trap. Depth of water seal in practice varies from 25 mm to 75 mm. The trap should contain water seal at all times. Causes which may remove the water seal are air compression, siphonage, momentum and evaporation.Requirements of a good trap:Following are the requirements of a good trap:

(1) It should be capable of being easily cleaned.(2) It should be easily fixed with the drain.

(3)lt should be free from any inside projections which are likely to obstruct the passage of flow of sewage.

(4) It should be of simple construction.(5) It should possess adequate water seal to fulfill the purposes of its installation.(6) It should possess self-cleansing property.(7) The internal and external surfaces should be of smooth finish.Types:The traps are classified in the following two ways: I. According to shape .II. According to use.Classification according to shape:According to shape, the traps are of three types: (1) P-trap (2) Q-trap (3) S-trap1) P-trap:This trap has the shape of letter P as shown in fig. 8-1.The leg of trap are at right angles to each other

(2) Q-trap: This trap has the shape of letter Q as shown in fig. 8-2. The legs of trap meet at_an_angle other than-a right angle.(3) S-trap:This trap has the shape of letter S as shown in fig. 8-3.The legs of trap are parallel.

Thus, the two legs of traps are at right angles, at an angles other than a right angle and parallel to each other in traps P, Q and S respectively.

Classification according to use:According to use, the traps arc of three types:(1) Floor trap(2) Gully trap(3) Intercepting trap.Floor trap:A floor trap is made of cast-iron and it is provided at the points of entry of waste water in the house. It will thus be placed in bath rooms, kitchen, sinks,etc. A floor trap forms the starting point of waste water flow.A cover with grating is provided at its top as shown in fig. 8-4 so as prevent the entry of solid matter. The cover can be removed for the cleaning of the trap. This trap is also referred to as nahni trap.

Gully trap:A gully trap is usually made of stoneware and a cast-iron grating is provided at its top. The gully trap is fitted inside a masonry chamber as shown in fig. 8-5. A water seal of about 60 mm to 70 mm ir provided in the gully trap.The gully trap forms the starting point of horizontal flow sewage. It is usually situated near the external face of wall and it is kept slightly higher or even in line with pavement or ground level. The gully trap leads the sewage either to sewer or to inspection chamber or to manhole.A well designed gully trap may serve two or three connections from the nahni traps. But it is advisable to provide separate gully traps for sullage and soil wastes. The top of gully trap chamber is provided with a cover, usually of cast-iron, which may be taken out easily to clean the trap.

(3) Intercepting trap:This trap has water seal of about 100mm and it is provided in the last manhole of house drainage system. It thus conveys sewage from house to the public sewer. Fig. 8-6 shows the manhole with intercepting sewer trap.The main idea of providing the intercepting sewer trap is to prevent the entry of sewer gases from public sewer line into the house drains:An intercepting trap is also known as an interceptor or a disconnecting trap and it contains an inspection arm for the purpose of cleaning or inspection. The inspection arm is kept closed by a lid or plug. A fresh air inlet is also provided in the manhole containing the intercepting trap.Provision of intercepting sewer trap is sometimes made compulsory by the local authority and it is thus a matter of policy of the local authority. It is interesting to note the merits and demerits of an interceptor.

Manhole with intercepting sewer trapMerits:Foul gases formed in public sewers are prevented from passing through the interceptor. If the interceptor is not provided, these gases will enter the vent pipes and they will be spreading in the surrounding atmosphere causing serious air pollution (ii) Harmful bacteria contained in public sewers are prevented from entering the house drains through the interceptor.(iii) Properly designed and constructed intercepting tap can remove quickly the foul matter obtained from house drains to the public sewer. Demerits:If discharge from house drains is small, the solid heavy matter may be retained in the trap and they may start decomposing.The purpose of interceptor will then not be served.If the lid or plug is not fitted properly or if it is broken,foul gases from public sewer will enter the house drains.Cleaning through inspection arm of the trap is difficult.

Interceptor itself forms an obstruction to the normal flow of sewage, (v) Omission of interceptor from house drainage is found not to present any serious difficulty.(vi) Presence of intercepting trap is found to affect seriously the ventilation of sewers, (vii) Provision of intercepting traps necessitates the,proper ventilation of public sewers. This increases the cost of public sewers. It also adds to the cost of house drainage.

Some definitions:Some of the following technical terms which are commonly used in connection with the house drainage will now be explained:(1) Anti-siphonage pipe:A pipe which is installed in the house drainage to preserve the water seal of traps is known as anti-sipkonage pie.. It maintains proper ventilation and does not allow the siphonic action to take place. The term siphonage will be discussed later on.

(2) Cowl:The top of vent pipes is provided with cowls so that the birds may not build their nests. Cowls are provided with slits or narrow openings.(3) Fresh air inlet:The last manhole which connects the house drain with the public sewer is provided with an inlet of fresh air This

(7) House drains are tested for water tightness and the trenches are then filled up.

Longitudinal SectionHorizontal Scale: lent = 4 m vertical Scale: lcm«2m

Longitudinal section of house drain

Testing of drains and pipes:After the house drains are laid and the pipes are fitted in position,it is necessary to ascertain their water tightness. For this purpose,various tests are applied. The drains are usually tested in sections between successive chambers and the vertical pipes are tested in groups,each

group having one common inspection chamber. Following are the tests which are commonly employed:(1) Air test(2) Coloured-water test(3) Hydraulic test:(4) Smell test.(5) Smoke test

(fj Air test:Air test can be applied for_underground and vertical pipes. The particular section is selected and plugs are provided at the upper and lower ends. Air is forced in the pipe by suitable equipment such as a pump. Leaky joint are found out by applying soap solution. The escape of air from leaky joints will form bubbles which are visible. These joints are then repaired.Coloured water test:When coloured-water is allowed to flow from one point to the other point of the drain, it will come out through the leaky joints. Thus, leakage can be detected suitable remedies may be applied to remove it from the joints.Hydraulic test:This is the most common test which applied for the water tightness of the underground drains. The lower end is provided with a plug and at upper manhole,water is filled to a height of about 60 cm to 90cm in case of house drains.Sweated joints are detected and repaired.Smell testThis test is similar to air test. But in this case ,the air is mixed with some smelling gas which can be easily recognized. Such air is allowed to pass through the drain. Escape of air from leaky joints is detected by smell and such joints are then repaired.

Smoke test:This test is similar to air test expect that smoke is introduced in the drains instead of air. The test is generally applied for detecting leakage in existing drains.