SOURCES OF WATER SUPPLYGENERAL INTRODUCTIONWater is the most abundant compound in nature. It covers 75% of the earthsurface. About 97.3% of water is contained in the great oceans that are saline and 2.14%is held in icecaps glaciers in the poles, which are also not useful. Barely the remaining0.56% found on earth is in useful form for general livelihood. Total quantity of wateravailable on the planet EARTH in various states and religions are given in the table 3.1

3.1 HYDROLOGICAL CONCEPTSHydrology is the science, which deals with the increment of the water on theground, under the ground, evaporation from the land and water surface and transportationfrom the vegetation and going back into atmosphere where it precipitates.3.1.1. DEFINITIONThe water which goes in atmosphere by evaporation and transpiration againcomes back in the form of precipitation under favourable climatic conditions is known ashydrological cycle of water.

Hydrological cycleFig 3.1 illustrates the hydrological cycle of water. Due to suns heat water fromthe earths surfaces, lakes, rivers, seas etc evaporates and rises upwards. At high altitudedue to reduction in the atmosphere pressure these water vapours expand by absorbingenergy from the surrounding air, which cools down. When it falls below the dew point itcannot retain the excessive moisture, which starts falling in the form of rain, hails, dew,sleet, frost or precipitation. Various factors such as temperature, atmospheric pressure,velocity of wind, height of mountains in the region, presence of forests, position of landand water areas etc and their complex relation are responsible for the precipitation. Thisprecipitation and evaporation processes continue forever and balance is maintainedbetween the two by nature.

3.1.2 PRECIPITATIONThe evaporated water from the surfaces of streams, rivers, sea, ponds, wetsurfaces, trees and plants etc again returned to the earth surface by the condensation inthe form of rain, hails, dew, sleet etc is known as precipitation. The major part of theprecipitation occurs in the form of rain and other forms quantities are very small. Thewater of precipitation further goes off in the following ways.i. RUN-OFF: After precipitation a portion of its water flows over the ground in theform of rivers and streams and some water flows towards lakes and ponds andcollected there.ii. INFILTRATION: A portion of precipitation, percolates in the ground and it isstored in the form of sub-soil or ground water.iii. EVAPORATION: some portion of the precipitation is also evaporated from thelakes, rivers, reservoirs and wet surfaces in the form of vapour due to suns heat isknown as evaporationiv. EVAPO-TRANSPIRATION: The roots of the trees sucks water from the groundand some portion of it evaporates in the atmosphere through leaves in the form oftranspiration.

SURFACE SOURCESAll the sources of water can be broadly divided into1. Surfaces sources and2. Sub surface sourcesThe surface sources further divided intoi. Streamsii. Riversiii. Pondsiv. Lakesv. Impounding reservoirs etc3.2.1 NATURAL PONDS AND LAKESIn mountains at some places natural basins are formed with impervious bed bysprings and streams are known as lakes. The quality of water in the natural ponds andlakes depends upon the basins capacity, catchment area, annual rainfall, porosity ofground etc. But lakes and ponds situated at higher altitudes contain almost pure waterwhich can be used without any treatment. But ponds formed due to construction ofhouses, road, railways conatins large amount of impurities and therefore cannot be usedfor water supply purposes.3.2.2 STREAMS AND RIVERSRivers and streams are the main source of surface source of water. In summer thequality of river water is better than mansoon.because in rainly season the run-off wateralso carries with clay, sand, silt etc which make the water turbid. So river and streamwater require special treatments. Some rivers are snowfed and perennial and have waterthroughout the year and therefore they donot require any arrangements to hold the water.But some rivers dry up wholly or partially in summer. So they require specialarrangements to meet the water demand during hot weather. Mostly all the cities aresituated near the rivers discharge their used water of sewege in the rivers, therefore muchcare should be taken while drawing water from the river.3.2.3 IMPOUNDING RESERVOIRSIn some rivers the flow becomes very small and cannot meet the requirements ofhotweather. In such cases, the water can be stored by constructing a bund, a weir or adam across the river at such places where minimum area of land is submerged in thewater and max. quantity of water to be stored. In lakes and reservoirs, suspendedimpurities settle down in the bottom, but in their beds algae, weeds, vegetable andorganic growth takes place which produce bad smell, taste and colour in water. Thereforethis water should be used after purification. When water is stored for long time inreservoirs it should be aerated and chlorinated to kill the microscopic organisms whichare born in water.SUBSURFACE SOURCESThese are further divided into(i) Infiltration galleries(ii) Infiltration wells(iii) Springs etc3.3.1 INFILTRATION GALLERIESA horizontal nearly horizontal tunnelwhich is constructed through water bearingstrata for tapping underground water nearrivers, lakes or streams are called Infiltrationgalleries. The yield from the galleries maybe as much as 1.5 x 104 lit/day/metre length ofinfiltration gallery. For maximum yield thegalleries may be placed at full depth of theacquifer. Infiltration galleries may beconstructed with masonary or concrete withweep holes of 5cm x 10cm.

Infiltration GalleryINFILTRATION WELLSIn order to obtain large quantity of water, the infiltration wells are sunk in seriesin the blanks of river. The wells are closed at top and open at bottom. They areconstructed by brick masonary with open joints as shown in fig. 3.3

Jack WellInfiltration Well For the purpose of inspection of well, the manholes are provided in the top cover.The water filtrates through the bottom of such wells and as it has to pass through sandbed, it gets purified to some extent. The infiltration well inturn are connected by porous pipes to collecting sump called jackwell and there water is pumped to purification plantfor treatment

4.5.3 Well Maintenance and Rehabilitation4.5.3.1 Cleaning Well Screens. A clogged well screen or a clogged aquifer nearthe well bore are the most common causes of decreasing yield. If the specific capacityhas dropped to 60 percent of the new well value, then cleaning the well screen canimprove the yield. If the specific capacity has dropped to 40 percent of the new wellvalue, it is usually necessary to redevelop the well. Well screens on deep wells can becleaned in place using one of the methods described below. Well screens can also bepulled for cleaning or for reuse.Several well screen cleaning methods are listed below. Also listed arethe paragraph numbers corresponding to a full discussion of the cleaning processes.

a) Acid Treatment. Encrustation of screens is caused principally bycalcium carbonate deposits and occasionally by iron oxide and calcium sulfatedeposits. Corrosion may also cause encrustation. Acidizing with properly inhibitedmuriatic acid or sulfamic acid cleans encrusted screens. Do not use uninhibited acids.The following procedures apply:(1) Estimate the severity of encrustation from the records ofchanges in yield, specific capacity, drawdown, etc.(2) Use an experienced and qualified contractor. Unlessotherwise directed by the utility manager, base personnel do not typically performacidizing operations. Be sure all people working on an acidizing project wear properprotective clothing.Caution: Before proceeding with the treatment, disconnect the well fromthe distribution system.(3) Use an inhibited acid. Wells are most often acidized usingmuriatic acid (commercial hydrochloric acid, 27 percent concentration) purchased with,or to which has been added, an inhibitor. These inhibitors are proprietary compounds:they keep the attack on the metal to a minimum but do not affect the reaction withcalcium carbonate. Select the inhibitor or inhibited acid to obtain the maximumprotection for the particular metal in the screen.(4) Add the acid carefully through a hose placed in the casewith its discharge end at the level of the screen. This procedure prevents dilution ofthe acid and gives a concentration of about 15 percent at the screen.(5) In typical situations, leave the acid in the well for at least5 hours. For quicker action, the acid may be heated, particularly if there is a flow ofwater past the well screen.(6) After the acid treatment, pump the well to waste until the pHof the water returns to normal.Caution: Provide for neutralization of this wastewater or other safedisposal until the water returns to normal.(7) Sulfamic acid (do not confuse with sulfuric acid) may beused in place of muriatic acid. Sulfamic acid is a granular solid that is safe and easy tostore and handle. It may be dissolved in water at the job site to provide a strong acidsolution that will do the same cleaning job as muriatic acid. Although sulfamic aciddoes not attack metals as rapidly as muriatic acid, inhibitors should still be used toprotect the casing. To dissolve iron oxide deposits on the screens, add 50 pounds(22.5 kilograms [kg]) of salt (sodium chloride) for every 100 pounds (45 kg) of granularsulfamic acid.(8) Reaction of the acid in the well produces carbon dioxide andhydrogen. If iron sulfide is present in the well screen, hydrogen sulfide gas is alsoproduced. Hydrogen sulfide is a toxic gas. Provide adequate ventilation in pumphouses or other confined areas when acidizing the screens. It is recommended that personnel avoid standing in pits or depressions adjacent to the well being treated.Carbon dioxide and hydrogen sulfide are heavier than air and settle in low areas.(9) Do not pump nearby wells when acid treatment is inprogress.(10) In addition to cleaning the well screen in place, the acidizingtreatment described above can be used to dissolve encrustations before pulling thewell screen. This treatment helps loosen the well screen in the well and makes it mucheasier to pull.b) Chlorine Treatment. Chlorine solutions may also be used to cleanwell screens. Chlorine added to a clogged well functions primarily by destroyingbacterial slime growths. Follow steps (1) through (3) below:(1) Prepare solutions of chlorine that produce 100 to 200 mg/L ofchlorine when mixed with the water in the well (Table 2). Introduce the solution into thewell using the procedure described for acid treatment (par. 4.5.3.1[a][4]).Materials Required for 100 Gallons (400 Liters)of Chlorine Solution

(2) Allow the well to stand for 24 hours. Then pump water towaste until the chlorine residual reaches 0.1 mg/L. Surging during chlorine treatment ishelpful (par. 4.5.3.1[g]).(3) Perform three or four successive treatments with chlorine.Alternating acid treatment with chlorine treatment can be very effective. Complete theacid treatment first, followed by chlorine treatment after most of the acid has beenpumped to waste. A second series of acid and chlorine treatments can be undertakenafter the initial acid and chlorine treatments have been completed.c) Phosphate Treatment. The glassy phosphates (sodiumhexametaphosphates) act as dispersing agents on such screen-plugging materials asamorphous silicia, hydrated ferric oxide, iron carbonate, and calcium carbonate. Followthese treatment steps:(1) Dissolve 15 to 30 pounds (7 to 14 kg) of glassy phosphatein a minimum amount of water and add 1 pound (450 g) of calcium hypochlorite foreach 100 gallons (400 L) of water in the well casing (under static conditions). Todissolve the phosphate, suspend the chemical in a wire basket or burlap bag. Do notsimply dump the phosphate in the dissolving tank or barrel. Add the solution to the wellthrough a hose using the procedure described for acid treatment (par. 4.5.3.1[a][4]).(2) Allow the solution to remain in the well for 24 to 48 hoursand surge approximately every 2 hours. If surging is not possible, allow the solution tostand in the well for 1 week.Caution: Treatment with glassy phosphate for more than 1 week maycause the well yield to decrease.(3) After treatment, pump the well to waste for 8 hours and testthe output. Repeat the treatment until the output no longer improves. Analyze thephosphate content of the well water after final treatment and pumping to make sure ithas been reduced to normal background levels.d) Dry Ice Cleaning. Compressed carbon dioxide gas, or dry ice,has been used for well cleaning with mixed results. This treatment works best in deepwells with high static levels. Follow these steps:(1) For wells measuring 6 to 10 inches (150 to 250 millimeters[mm]) in diameter, use 10 to 15 pounds (4.5 to 7 kg) of dry ice for light surging and25 to 50 pounds (11 to 23 kg) for heavy surging. Drop pieces of broken dry ice ofabout 2 inches (5 centimeters [cm]) in diameter into the well casing until enough hasbeen added to blow the water through the screen. The water will not freeze if there are11 pounds (5 kg) or approximately 1.5 gallons (5 L) of water in the well casing for eachpound (450 g) of dry ice added.(2) Provide a pressure gage on the well casing and seal thewell to prevent loss of carbon dioxide. When the gas is released, it expands andcreates a surging action that produces backpressure and backwashing of the screens.The escape of gas through the water-bearing strata will be evident from irregularmovement of the pressure gage needle. The particular conditions involved aredifferent in practically all cases, and the exact procedure depends largely on theoperators judgment.Caution: Dry ice may cause burns if handled with bare hands. Useheavy gloves or tongs. Also, since high pressure may develop during dry icetreatment, provide for control and release of excessive pressure (150 psi or 1,030 kPa).The gas is suffocating. Provide ample ventilation.e) Jet Cleaning. Horizontal jet cleaning of wells is performed frominside the well screen. The process requires only a relatively simple jetting tool, alongwith a high-pressure pump, a hose, a string of 2-inch (50-mm) pipe, and an adequatewater supply. The jetting tool itself is shown on Figure 3. It consists of an attachmentfitted with one to four horizontal nozzles (3/16-, 1/4-, or 3/8-inch [5-, 6-, 10-mm])orifices. The bottom of the tool is closed. The upper end is threaded so that the toolcan be screwed into the lower end of the string of 2-inch (50-mm) pipe. Follow thesesteps to jet clean a well screen:(1) Select a nozzle to match the output of the high-pressurepump used and the well pump (Table 3).

SPRINGS:Sometimes ground water reappears at the ground surface in the form of springs.Springs generally supply small springs. Springs generally supply small quantity of waterand hence suitable for the hill towns. Some springs discharge hot water due to presenceof sulphur and useful only for the curve of certain skin disease patients.

Types of springs:1. Gravity Springs: When the surface of the earth drops sharply the water bearingstratum is exposed to atmosphere and gravity springs are formed as shown in fig.3.5

Gravity Spring2. Surface Spring: This is formed when an impervious stratum which is supportingthe ground water reservoir becomes out crops as shown in fig.3.6

Surface Spring3. Artesian Spring: When the ground water rises through a fissure in the upperimpervious stratum as shown in fig.3.7

Artesian SpringWhen the water-bearing stratum has too much hydraulic gradient and is closedbetween two imperious stratum, the formation of Artesian spring from deep seated spring

Artesian Spring3.3.4. WELLS:A well is defined as an artificial hole or pit made in the ground for the purpose oftapping water. In India 75 to 85% of Indian population has to depend on wells for itswater supply.The three factors which form the basis of theory of wells are1. Geological conditions of the earths surface2. Porosity of various layers3. Quantity of water, which is absorbed and stored in different layers.The following are different types of wells1. Shallow wells2. Deep wells3. Tube wells4. Artesian wells3.3.4 (a) Shallow Wells :Shallow wells are constructed in the uppermost layer of the earthssurface. The diameter of well varies from 2 to 6 m and a maximum depth of 7m.Shallow wells may be lined or unlined from inside. Fig. 3.9 shows a shallow wellwith lining (steining). These wells are also called draw wells or gravity wells oropen wells or drag wells or percolation wells.

Shallow WellQuantity of water available from shallow wells is limited as their source of supplyis uppermost layer of earth only and sometimes may even dry up in summer. Hence theyare not suitable for public water supply schemes. The quantity of water obtained fromshallow wells is better than the river water but requires purification. The shallow wellsshould be constructed away from septic tanks, soak pits etc because of the contaminationof effluent.The shallow wells are used as the source of water supply for small villages,undeveloped municipal towns, isolated buildings etc because of limited supply and badquality of water.3.3.4 (b) Deep Wells :The Deep wells obtain their quota of water from an aquifer below the imperviouslayer as shown in fig No. The theory of deep well is based on the travel of water from theoutcrop to the site of deep well. The outcrop is the place where aquifer is exposed to theatmosphere. The rain water entered at outcrop and gets thoroughly purified when itreaches to the site of deep well. But it dissolves certain salts and therefore become hard.In such cases, some treatment would be necessary to remove the hardness of water.

Deep WellThe depth of deep well should be decided in such a way that the location of outcrop is not very near to the site of well. The water available at a pressure greateratmospheric pressure, therefore deep wells are also reffered to as a pressure wells.3.4 INTAKES FOR COLLECTING SURFACE WATER:The main function of the intakes works is to collect water from the surface sourceand then discharge water so collected, by means of pumps or directly to the treatmentwater.Intakes are structures which essentially consists of opening, grating or strainerthrough which the raw water from river, canal or reservoir enters and carried to the sumpwell by means of conducts water from the sump well is pumped through the rising mainsto the treatment plant.The following points should be kept in mind while selecting a site for intakeworks.1. Where the best quality of water available so that water is purified economically inless time.2. At site there should not be heavy current of water, which may damage the intakestructure.3. The intake can draw sufficient quantity of water even in the worest condition, whenthe discharge of the source is minimum.4. The site of the work should be easily approchable without any obstruction5. The site should not be located in navigation channels6. As per as possible the intake should be near the treatment plant so that conveyancecost is reduced from source to the water works7. As per as possible the intake should not be located in the vicinity of the point ofsewage disposal for avoiding the pollution of water.8. At the site sufficient quantity should be available for the future expansion of thewater-works.Types of Intake structures:Depending upon the source of water the intake works are classified as following1. Lake Intake2. Reservoir Intake3. River Intake4. Canal Intake1. LAKE INTAKE:For obtaining water from lakes mostly submersible intakes are used. Theseintakes are constructed in the bed of the lake below the water level; so as to draw water indry season also. These intakes have so many advantages such as no obstruction to thenavigation, no danger from the floating bodies and no trouble due to ice. As these intakesdraw small quantity of water, these are not used in big water supply schemes or on riversor reservoirs. The main reason being that they are not easily approachable formaintenance.

Lake IntakeRIVER INTAKE

Water from the rivers is always drawn from the upstream side, because it is freefrom the contamination caused by the disposal of sewage in it. It is circular masonarytower of 4 to 7 m in diameter constructed along the bank of the river at such place fromwhere required quantity of water can be obtained even in the dry period. The water entersin the lower portion of the intake known as sump well from penstocks.River Intake

RESERVOIR INTAKE:Fig 3.13 shows the details of reservoir intake. It consists of an intake well, whichis placed near the dam and connected to the top of dam by foot bridge.

Reservoir IntakeThe intake pipes are located at different levels with common vertical pipe. Thevalves of intake pipes are operated from the top and they are installed in a valve room.Each intake pipe is provided with bell mouth entry with perforations of fine screen on itssurface. The outlet pipe is taken out through the body of dam. The outlet pipe should besuitably supported. The location of intake pipes at different levels ensures supply of waterfrom a level lower than the surface level of water.When the valve of an intake pipe is opened the water is drawn off from thereservoir to the outlet pipe through the common vertical pipe. To reach upto the bottomof intake from the floor of valve room, the steps should be provided in Zigzag manner.CANAL INTAKE:Fig 3.14 shows the details of canal intake. A intake chamber is constructed in thecanal section. This results in the reduction of water way which increases the velocity offlow. It therefore becomes necessary to provide pitching on the downstream andupstream portion of canal intake.Canal Intake.The entry of water in the intake chamber takes through coarse screen and the topof outlet pipe is provided with fine screen. The inlet to outlet pipe is of bell-mouth shapewith perforations of the fine screen on its surface. The outlet valve is operated from thetop and it controls the entry of water into the outlet pipe from where it is taken to thetreatment plant.