Water supply in Mumbai - Rainwater Harvesting

IntroductionMumbai, is one of its 10 mega cities of the world and business capital of India. Mumbai proper occupies alow-lying area that once consisted of seven islands called Colaba, Mazagaon, Old Woman's Island, Wadala,Mahim, Parel, and Matunga-Sion separated from each other only during high tide. The population has risenfrom merely 3 millions in 1951 to 12 millions as on 2002 out of which 50 % live in slums It also supports“daily commuting” population of 20 lakhs It covers an area of 437 sq.km. With average density of 36600soul/ sq.km.Water Supply-From Past To PresentPrior to 1870, the Mumbaikar used to drink water from the existing well, lakes and tanks. But during middleof nineteenth century, because of the epidemic, decision was taken to build a dam to supply good quality ofpotable water, and then onwards Bombay water works started functioning The history of Mumbai’s watersupply dates back to the 22nd June 1845. On this day, the then Government in response to the agitation ofthe native appointed 2 men Commission to report about the quality and quantity of water available inMumbai. The Commission reported back within 24 hours that the water supply of Mumbai neededimmediate attention. This was the beginning of efforts to search sources of water to satisfy the City’sdemand. It is the first city in India to receive piped water supply in the year 1860.Today it supplies 2950 MLD every day, is one of the largest water supply in Asia. Sources ofSupplies are four lakes namely Tansa, Vaitarna, Vehar and Tulsi. about 110 km from Mumbai.The water istreated in two plants namely Panjarapur & Bhandup and stored at two Master Balancing Reservoirs namelyYewai & Bhandup with 1910 MLD ,the largest water treatment plant in Asia and further supplied to the citythrough 26 service reservoirs. The entire network is spread over an area of 430 sq km, while the sources are40 to 60 kms away from the Master Center.WATER SUPPLY TO GREATER MUMBAISNO Source of water supply Daily supply in mld Year since it commissioned1 Vihar lake 67 18602 Tulsi lake 18 18793 Powai lake 4 18914 Tansa river scheme 494 19485 Vaitarna- cum-Tansa scheme 490 19576 Ulhas river scheme 90 19677 Upper Ulhas scheme 550 1972-73Source : CGWB manual on groundwater in urban environment of IndiaHow Much Is Supplied?The Brihanmumbai Municipal Corporation is responsible for providing water supply, managing andoperating the network and billing and collecting revenues to the population of Greater Mumbai ( more than12 million people). The department in charge of these functions is the Hydraulic Engineer’s department.There are around 300,000 water connections in Mumbai.Most of the supply is for domestic purposes ( 85 %). The non-domestic demand ( 15 %) has beendecreasing over the years in parallel with the decline of water consuming industries ( mostly textile anddairies).The Municipal Corporation of Greater Mumbai presently supplies water at 135 LPCD to the

consumers in planned development, which is recently curtailed to 90 LPCD because of rapid rate ofdevelopment, constant influx in the city and no augmentation in water supply in near future.City today needs nearly 4000MLD of water. With anStatus of water supply in Mumbai expected population growth of 2% per year, the3800projected water demand in 2011 will be 4500MLD.4000Water is supplied at the rate of 2980 MLD from29503000surface water. Average supply is around 240 to 2502000lpcd. However large discrepancies exist according tothe type of settlement and the type of connections.1000Surface water provided to the city by a gravity system0is the main characteristic of the supply of MumbaiDEMANDSUPPLY where groundwater plays no role. Water is supplied onsource: Braham Mumbai Corporation a rotational basis among the 107 distribution zonesbecause of the reservoirs capacity. Intermittent supplyis the rule in Mumbai and supply can vary from two tosix hours.Million litres per dayWho Needs How Much?WATER REQUIREMENT OF GREATER MUMBAI(1991,2001,2011)Water Requirement(in MLD)500040003000200010000308022001489Domestic400 400 400Industrialinstitutional45253819352928232521201738 54 69 90 90 90Other uses Enroute Total (net) Total ( gross)Type of UseNote : The projected demand of water for Greater Mumbai for the year 2021 is estimated to be 5355 mld.Source : CGWB manual on groundwater in urban environment of IndiaSITUATION ANALYSISOut of the gross water supply of 3,193 MLD, after accounting for leakages, the net availability amounts to2,320 MLD. This includes 600 MLD water supply for non-domestic purposes, namely, industry andcommerce. The water losses through leakages in water supply distribution system amount to almost 25%.This is very high despite the MCGM efforts to reduce the same to 15%.

Capacity(MLD)700600500400300200100067ViharlakeSOURCES OF WATER SUPPLY18 4TulsilakePowailake494Tansariverscheme590Vaitarna-cum-Tansa90Ulhasriverscheme550UpperUlhasscheme*Expected year of completion-Gargai-2009 & Shai-2009.* The average gross per capita water supply is 260 litres, while the net water available for domestic use isabout 155 litres per capita per day (lpcd). This net availability no doubt exceeds norm of 135 lpcd set by theBureau of Indian Standards (IS). Apparently, the water supply status appears to be satisfactory on thewhole. However, the fact that there are a good number of private water suppliers and a conspicuously largemarket for water provides elegant testimony of inadequacies of water management in the city.* Surely, the aggregates should not give any complacency to the municipal authorities. The spatial,temporal and sectoral coverage of water is still missing i.e., some parts of the city do not receive water;some of them receive it intermittently; and some sectors have more privilege in accessing it than others.Connection Nature of Use Tariff (Rs per thousand litres)Metered:Domestic-Slums/Chawls 2.25-High rise buildings 3.50Commercial/Industrial 10.50 - 38Unmetered: Domestic 65% of the rateable valueCommercial/Industrial 130% of the value rateable valueSource: Municipal Corporation of Greater Mumbai (2002)Moreover, the municipal norms of water supply have been fixed at 45 lpcd in slums, 90 lpcd in chawls and135 lpcd in high rise buildings, respectively. However, the actual water supply widely varies between wardsand even localities within a ward. For example, it varies from 50 lpcd in slums to 250 lpcd in high risebuildings.What Will Be The Future Supply?FUTURE SOURCES OF WATER SUPPLY865455350455BHATSA (MUMBAI III A)MIDDLEVAITARNAGARGAIPINJALThe present supply versus demand percentage satisfactionis about 76 %. Looking to the growth of city and day- bydayincreasing demand, there is an urgent need to identifyand commission new sources of water supply. Govt ofMaharashtra has allotted additional 350 MLD of waterfrom Bhatsa sources. This project is known sa MumabaiIII-A project.

This project has been taken up on priority basis to utilise this additionalwater from Bhatsa source. The estimated cost of this project is Rs 700crore. This project is expected to be completed by the end of year2007.The important components includes several works like raisingheight of Pise weir by 2m (work completed ) ,laying of 3000 mm diamain from Pise to Panjrapur(total length about 9 kms Part of the work of 3 kms iscompleted.),pumping station at PiseTreatment plant of 455 MLDcapacity at Panjrapur, raw water pumping station of 635 MLD capacityat Panjrapur ,tunnel from Bhandup comlex to Malad Hill reservoir and further extension upto LibertyGarden and Charkop,tunnel from Veravli Hill reservoir to Oshiwara and Yari road.and laying of 3000 mm dia water main fromMulund Goregaon link road to Amar Mahal along Eastern Express HighwayThe future sources of water supply to Mumbai city to fulfil the requirment have been identified.The identified sources and the estimated yield from each source is Vaitarna river basin and Ulhas riverbasin are as under:Capacity(MLD)10005000Vaitarna River Basin455 455MiddleVaitarnaGargai865PinjalWater from sources in Vaitarna river basin can bebrought to city by gravity. The feasibility reportfor Middle Vaitarna project has been completed.The final technical details like type of dam, etc.isbeing worked out. Most of the clearances requiredhave been obtained. However, clearance fromEnvrionmental Department of Govt. of India isyet awaited.The major components of works identified in Middle Vaitarna project includes a location of dam betweenUpper Vaitarna & Lower Vaitarna, tunnel of 3500 mm dia length of 8 kms from Modak Sagar ( vaitarna) toY-branch ,a 3000 mm dia water main between Y- branch and Gundavali for a length of about 33 km indifferent stretches and additional treatment plant at Bhandup complex of 590 MLD capacity.For Gargai and Pinjal sources the water can be transmitted to Modak Sagar through tunnels by gravity.Further from Modak Sagar water can be easily brought to Bhandup complex with existing and additionalconveyance system.It would be beneficial to tap sources from Vaitarna basing from where water can be brought by gravity uptoBhandup complex where, adequate land for accommodating additional treatment plant and to enhance thecapacity of Master Balancing Reservoir – I is available at appropriate elevation. The treated water can bepumped into Master Balancing Reservoir at a fairly low head ( 18 m) . This would save operative cost andconserve electric power.Ulhas River BasinCapacity(MLD)1500100050001090590Kalu ShaiThe water from Ulhas river basin has to be abstracted andconveyed by pumping. Two stage pumping is necessary i.e.,from pick up weir at Pise to treatment plant at Panjarapur, andfrom treatment plant to Master Balancing Reservoir – II atYewai Hill. Looking to the problems that have arised inpumping system in the last two decades, it will be beneficialto minimize pump supply and to adopt gravity supply to theextent possible.

Advantages of gravity system of water supply from Vaitarna river basin compared to pumping system ofUlhas river basin includes less prone to pollution at source than that abstracted from Ulhas river basin.Secondly, cost effective as saving of about Rs 50 crore per annum in operative cost. Thirdly, comparativelyassured water supply due to non- dependency on power supply. Fourthly, land required for locatingtreatment plant facilities and for laying transmission system is already available with Municipal Corporationof Greater Mumbai ( MCGM).Fifthly, population affected by developing sources of vaitarna basin iscomparatively much less.Sixthly,the numbers of villages need resettlement are 8 as against in Ulhas basin.moreover the area under submergence is less, in vaitarna basin 3473 hectatres as against 5108 hectares inUlhas basin .Lastly it requires recurring expenses on maintenance of electrically operated system due tolimited electrically operated system.Water Pricing – Who is Paying how much?Consumers have to pay water and sewerage charges when the connection is metered, and water andsewerage tax when the connection is not metered, water and sewerage benefit tax for all consumers. Since1995-1996, the total revenue income has doubled while the expenditure has increased by 1.5 times. All theproposals to separate the water supply and sewerage department and to create a water board have beenrejected by the corporation. In order to improve the cost to recovery (today;80 %), the centralisedcomputerised billing is being decentralised at the ward level.Till as late as May 1997 the water charges were as low as 60 paise/ 1000 litres and after that tariffs arerevised three times and present rates are adopted with effect from 01.08.2002.Water charges are as follows ( Rs. Per cu m):For domestic consumers: Rs 1.75 for slums and Rs 3 for othersFor hospital, hall et al: Rs 8For industrial establishments: Rs 15For commercial establishments and other industries : Rs 22For 3 star hotels : Rs 35In addition, consumers are also required to pay water benefit tax at 12.5 %. Also, as 70 to 80 % of watersupplied exits as sewage, sewerage charges are collected at a rate of 60 and 39 % of water charges in caseof metered and non-metered connections, respectively. For commercial/industrial units, this is 78 per cent.This hike ( from 1.75 to 2.25 Rs. Per cubic meter for slum dwellers and from Rs 3 to 4 for other domesticusers) will, according to estimates , bring an additional Rs 51 crores to the BMC’s revenue ( the Times ofIndia, 2002)The tariff classification under water charges rules is as under:Category of consumer Tariff in Rupees per 1000litres*DomesticStand postBuildings & chawls2.253.50Halls, Hospitals, Playgrounds, Swimming pools etc. 10.50Industries, Dhobi ghats, Central & State government premises etc 18.00Shops, Restaurants- I, Cinema Halls, Refineries, Airports, Public sector 25.00undertakings etc.,Race course & Star hotels 38.00• Note : Sewerage charges are at 60 % of water charges.

Since 1987, domestic rates have been multiplied by five and 10 respectively for slums and others. Othertariff categories have also been increased but to a lower extent ( less than three times for commercialestablishments for instance). Sewerage charges are equal to 60 % of the water charges since April 2000 andhave to be paid whether or not they have a connection, a situation similar to the one in Chennai. Water andsewerage charges are collected every four months if the bill amounts is below Rs 3,000 and every monthotherwise. The bill collection is carried out by the Hydraulic departmentComparision of water charges billed for different cities in India with different levels of consumptionSTATE\AGENCYWater Tariff(Rs/KL)DOMESTICHyderabad MunicipalWater Supply &SewerageAhmedabad MunicipalCorporationNagpur MunicipalCorporationMadras Water Supply&SewerageDelhi Jal Board Upto 10KL/ month@35paise/KL +50%Above 10KL and upto 20KL/month @ Rs1/KL+50% Above 20KLand upto 30KL/month@1.50/KL+50%Above 30 KL/month @Rs 3+50%WaterTariff(Rs/KL)COMMERCIAL3-10 6-12 6-121.50 4.00 4.002-2.50 4.00 10.0030(Flat) 10.00 25.00Upto 50 KLs/month@ Rs 5/KL+50%Above 50 KLs @Rs10/KL+50%Minimum Charges @rs 100+50% permonth/connectionWaterTariff(Rs/KL)INDUSTRIALCalcutta Municipal 5.00 100-200/monthDevelopmentAuthorityBangalore Water Rs 65 upto 25 KL @ Rs Rs 275 upto 10 KL Rs 60/KLSupply &Sewerage 2.60/KL for more than for more than 100 KLBoard100 KL,Rs 33/ KL. Rs 60/KL.Tamil Nadu Water 2.00 4.00 6.00Supply & SewerageSource:P.S.Rana,Integrated Urban Infrastructure In vestment and HUDCO’s Lending Programme,PaperPresented in the International IHSP seminar on ‘Integrated Urban Infrastructure Development held on 1-4February,1995 ,New Delhi, in Urban Statistics, Handbook 2000,NIUA,New Delhi,pp-103-104S.K.Rohilla et.al,Delhi’s Water AND solid Waste Management-Emerging Scenario.To sum up, cross- subsidies are the rule as in many other Indian cities as industrial and commercialestablishments have to pay much higher rates than domestic connections. However, unlike most of othercities, slum dwellers (in recognised settlements) are considered as customers and have to pay water andsewerage charges and taxes. In any case, the tariff policy is not based on economic principles and no changeof tariff structure is thought of. Water supply and sewerage is a good source of revenue in Mumbai but the

lack of independence from the corporation, for instance through a board, is a constraint towards efficientmanagement.Water Leakages-What is the scenario?The leakage study world over indicated that the wastage of water, more popularly know an Unaccounted forwater ( UFW), ranges from 8 % to 12 % for developed countries and same for the developing and nondevelopedcountries is in the range of 20 % to 70 %. In Mumbai the estimated UFW is in the range of 20 %to 25 %. The 15 % leakage is considered as acceptable in a distribution system because further reductionefforts are not cost effective.In Mumbai the waste prevention programme was systematically implemented, by introducing a LeakDetection ( LD) Cell, since 1973. The entire city is divided in 615 leak detection zones. Water mains ineach zone were thoroughly checked for leakage by sounding instruments periodically. The initial leakageand losses after attending repairs to defective mains were compared to arrive at quantity of water saved. Theprocess was laborious and in fact with diligent efforts the total leakage was brought to about 15 % by mideighties.This was very close to acceptable limits of allowable leakage in a distribution network.Pipe Lines-are they sensitive to weather condition?The water supply system of Mumbai is of intermittent type and thus water mains are subjected to alternatewet and dry conditions, a very conductive condition for corrosion and rusting. The materials of water mainsconstituting conveyance, distribution and communication network are Mild Steel, Cast Iron, Ductile ironand Galvanised iron. Recently High Density Poly-Ethylene ( HDPE) , Medium Density Poly Ethylene(MDPE) and Glass Reinforced Pipes ( GRP) material also used for laying pipelines in particularly hostileconditions and creek lands.Thus in Mumbai, even in the most hostile surroundings, the water mains of different materials areadequately protected against corrosion by adopting various anti- corrosive measures by MCGM.Where Waste Goes?Mumbai generates 5,500 metric tons of organic and inorganic waste daily. Only about 5,000 tons arecollected daily by the BMC, which spends approximately Rs. 135 crores a year for garbage collection anddisposal. There are 6.300 garbage collection points in the city and its suburbs. Citizens do not pay a specialtax for garbage clearance. BMC employees and contractors lift the garbage and deposit it in the fourdumping grounds at Deonar, Malad, Gorai and Mulund. The Deonar grounds take about 70% of the total.The capacity of these landfills will expire around the year 2010.BMC employs about 20,000 workers for solid waste management. Each worker is paid Rs. 3,200 permonth, around Rs. 3,000 travel allowance, and up to Rs. 1.25 lakhs in housing loans with minimal interest.In 1988 a report on the health of BMC workers pointed out that 67% of the workers complained of choking,breathlessness and sever burning sensations in the eyes each time they went down a manhole; that spinescollapsed from the cramped working conditions; that skin disease and gastrointestinal tract infections wereso commonplace as to be beyond comment.Collection, Transportation & Disposal of Town Solid WastesQuantity of Average Solid Waste collected daily is 4,000-4500 tonnes of refuse(Approx) and 2,000-2500tonnes of debris and Silt (Approx.) The total staff for Conservancy and transport is 35,601, 4244respectively. The total expenditure of 1999-2000on conservancy is Rs 323.6 Crores (Approx) and ontransport is Rs.79.37 Crores (Approx.).Total No. of vehicles used for refuse collection. is 953 for refuseplus debris(Contractor) and 509 (Refuse) + 731 other service Municipal vehicles .Land filling methods,processing/treatment to convert into manure,pelletisationand vermi composting are different modes of disposal. The main dumping grounds are at Deonar ,Mulund,Chincholi and Gorai (Borivli).

According to survey, the pollution levels are very high in Khar and Maravali and pollution of the MithiRiver is a cause for concern. The city produces 2671 MLD of sewage and 6256 MTD of solid waste.SewerageSewerage for the city is managed by the Water Supply and Sewerage Division of the BMC. Only about80% of the city's area has sewerage. There is a pumping station with a marine outfall at Love Grove inWorli. A similiar pumping station at Bandra is planned, as are aeration lagoons for treatment of sewage atMalad, Versova, Ghatkopar and Bhandup. Information on a World Bank loan for a water supply andsewage disposal project can be accessed. This program has also received Japanese aid.The Ghatkopar and Bhandup stations, with their Waste Water Treatment Facilities are expected to startfunctioning by 1998. The plan for a lagoon at Malad has been cancelled because the Malad creek is unableto carry sewerage. The National Environmental Engineering Institute (NEERI) will check the quality ofcoastal water at the outflow from the Versova lagoon.An Indian firm, AIC Watson, is performing the topographical survey for an assessment of the water leveland conditions of manholes in the city. A German form, GKW, is preparing a detailed report on thestructural condition of the city's sewerage pipeline. A Canadian firm, R. V. Anderson and Co, is conductinga survey of the operation and maintenance of the entire sewerage disposal system, including the humancomponent such as information systems, staff etc.Sea water or Sewage Water?Water pollution in Maharashtra goes unchecked.90% of sewage water generated by municipal councils andover 50% of sewage discharged by municipal corporations goes untreated, CAG said in its latest report.This untreated and treated waste mixed with industrial effluents, was discharged through seven outlets. Ofthis 1594 MLD was directly discharged in to Arabian sea and 973MLD was discharged into creeks thaneventually merged with the sea, makes it highly polluted and unfit for bathing, water sports and commercialfishing.Is Water Quality Is A Issue?Despite the result of the study conducted by Dr M M Bapat and Dr T N Mahadevan (1999-2002 ) whichtalks about the physical, chemical and bacteriological aspects that they should satisfy and the desiredquality of water must be maintained up to the point of ingestion of the consumer. Though the result of thereservoir water analysis clearly indicate that the quality of water being supplied to the city of the Mumbai,at the point of supply, is unquestionable and at par with international standards ,the levels of bacteriologicalpolluted is more than 20 % in most of the wards, the maximum being 70 % in ward M/E. Hence, attemptswere made to located the probable causes. The contamination of water supply were largely due tounsanitary conditions of surrounding,. negligence towards hygiene, no timely cleaning and maintenance ofunderground suction tanks and overhead distribution tanks situated in the residential areas. While,infiltration of sewage through water mains is because the drinking water mains and sewerage pipe linesrunning parallel to each other. In some localities the drinking water connections run through puddles ofsewage water, defecation on the mains by slum dwellers and because of leakages in service connectionsAlmost all the co-operative housing societies in Mumbai invariably practice storage of water inunderground tanks (UG) during the restricted supply hours and regulate supply to residents by pumping intooverhead tanks (OH) twice a day depending on availability of water. Wastage of water due to overflowsfrom both storage facilities were seldom seen since the supply is relatively limited.Most of the residents also store the water in their premises for various utilities including cooking since thedemand supply position supply position is not matching well. Use of the commercial water purification kidswith either UV or other sterilization methods were practiced at least in 20 % of the housing coloniescovered. Even this depended on the socio- economical status of the residents.Since the BMC distribution network is dry for a major interval of time everyday causing partial vacuum inthe system, the chances of sewage or other wastewater getting sucked into the pipeline through inadvertentperforations in the pipeline cannot be overlooked especially in areas where the municipal water lines runalong sewage water pipes or are submerged in the wastewater. Overflow of raw sewage system could beseen invariably in many locations.

A few recognised slum colonies who also enjoy all the municipal service facilities were considered. Theseinclude : Atomica Society, Narayan Guru Society, Assisi Nagar, Chempazhanthi society, Sri Narayanasociety, Sankara society, Buddha nagar, Gautam Nagar. Samples were collected at the time of supply, fromstorage tanks, at house levels with and without filtration, Aqua Guard water etc. A total of 160 samples formicrobial and 80 for chemical parameters were analysed. 70 % of the samples analysed for MPN werefound to be contaminated. Even Aqua Guard filter indicated sporadic contamination by MPN when inexcess.. Nitrite concentrations were also high as compared to other areas. Sediments and some organismswere also noticed during the survey period.The analysis of bore well water sampled from areas in and around Mumbai led to the observation thatnearly all the parameter values ( chemical as well as microbial) were quite high as compared to the valuesseen in case of the municipal water supply samples. Many of the samples crossed the permissible limitvalues of BIS in the case of Alkalinity, Total Dissolved Solids ,Total Hardness, Calcium, Hardness andMagnesium hardnessMost of the samples were found to be unpotable with respect to the microbiological parameter ( MPN) aswell, since the Faecal Coliform counts exhibited by these samples were generally _> 1600 FC / 100 ml.Rain Water Harvesting-Reclaimed land and threat of salinity, quality of water—of both municipal supply and tankers., unequaldistribution, wasteful consumption pattern—leading to over withdrawal from sources—heading for urbanruralconflict?, Therefore, overall water management is the order of the day—with RWH as a keycomponentWhat Government Is Doing?Mumbai Municipal Corporation has made rainwater harvesting mandatory to the properties having plot areamore than 1000 sq.mts. coming for development after 1st oct 2002. The condition is also being extended forthe properties, which started development earlier, but are being completed now. These conditions will alsobe made applicable to existing buildings in near future. Recycling has been made compulsory for buildingshaving centralised (water cooled) A.C.plants. Henceforth M.C.G.M would grant residential waterconnections at 90 lpcd. No municipal water for flushing requirement. The properties are expected togenerate the flushing water either by Rainwater harvesting or by recycling.On 14th Feb.2002, Water supply & Sanitation Department of Government of Maharashtra has issued a G R.approving Rain Water Harvesting as a means of improving water supplies. The G R details varioustechniques of rain water harvesting, their costing & availability of funds. In furtherance Municipalcorporation of Greater Mumbai has issued a Circular insisting provisions for rainwater harvesting whiledeveloping plots having area more than 1000 sq mts, as I.O.D. conditions from 1st Oct. 2002. The design ofrainwater harvesting system shall be prepared by approved consultant in the field & shall be to satisfactionof the corporation. Further all centrally air conditioned building shall have their own waste water treatmentplant & treated waste shall be used for cooling purposes.Rainwater Harvesting Potential In Mumbai-Is It Viable?700To look at potential of rainwater harvesting it is essential to look at the climate, especially rainfall pattern .The climate is equable with very little seasonal fluctuation. January, the coolest month, has a meantemperature of 24 deg C May, the warmest month,42 YEARS MEAN TOTAL PRECIPITATIONaverages 30 deg C Seasonal fluctuations of humidity andrainfall are more significant than those of temperature650600566IN MILLI METRES50040030020010000 0 0 0 12487355885 0JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecember

MEAN NUMBER OF PRECIPITATION DAYS302524.9 25NO. OF DAYS201510500.1 0.1 0.1 0.3 0.917154.81.60.3JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecemberThe average annual rainfall is 2,170 mm (85 in). Because of the southwest monsoon winds, more than 95percent of the annual rainfall occurs during the four-month period of June through September. Mumbai alsohas high humidity, with an annual average of 87 percent.Area of Mumbai – 437 sq kmsAnnual avg .rainfall – 2000 mmTotal rainwater falling over Mumbai= 437 x 1000000 x 2000 lit= 874000000000= 2394.52 MLDPresent water supply = 2900 MLDEven if we assume 70 % of the area to be developed, 50 % of it to be roofed and we collect 70 % of thewater falling over it, the quantity of rainwater that can be harvested works out to 589.34 MLD. This is asizeable quantity compared to water supply to Mumbai.Are You Interested-What Needs To Be Done ?One has to get the approval of designs from the rainwater harvesting cell. headed by Ms Suprabha Marathe,Assistant Engineer. The office is located at 5 th floor, Municipal head office, Mumbai. The cell is alsohaving braches at its 24 wards that cater the need of the public. Ms Marathe says it is necessary to centralizebecause rainwater harvesting should not lead to contamination of underground aquifers.A person who wantsto rainwater harvesting has to send to BMC the society plan showing building, water requirement of thesociety, roof size, area of open premises and also details of suction tanks , septic tanks, flushing networkand inspection chamber position. And if they have any borewell then its details has to be given Once aclient submits his plan they the RWH cell superimpose the design on the drainage map and ensures thewater harvesting structures do not affect the existing water line and sewage lines. More over the cell alsogoes to the site to ensure that quality of the work is maintained.Challenges !Ms Marathe says that rainwater harvesting will be challenge in Mumbai, considering the existing conditionin Mumbai, like easy available of municipal supply and at cheaper rate. More over the geology is alsocomplicated in Mumbai. She says that previously the Mumbai was a group of seven islands; the gapsbetween the islands were filled up in due course. So in one place a person may get water at 3 ft and other

place one might touch water at around 70 or more depth. So according to her considering the situation thesuccess of rainwater harvesting in Mumbai can be taken a big success story unlike the other Indian cities.She further told that she has deliberately taken up sites where the seawater intrusion has taken place and thecell will be monitoring the water quality in these wells. To find out the improvement of water quality byrainwater harvesting, She further told that rainwater harvesting is at the early stages and it will take the endof the year to actually say the impact of water harvesting in Mumbai.She said that the to create awareness among the public cell in the last six months have conducted workshopsfor Architect, Plumber and Engineers. According to her in mumbai both recharge and storage methods arepracticed. The old abandoned storage tanks were repaired and used for storage purpose and the excess.CASE STUDIES1.BACK BAY DEPO, THE BOMBAY ELECTRIC SUPPLY AND TRANSPORT (BEST),MUMBAI.Case BackgroundThe rooftop area of the shed is about 350 sq.m. The main source of water for the Back Bay Depo was frommunicipal supply. BEST is having 25 bus depose in Mumbai, among them currently around 14 bus deposare having rainwater harvesting storage tanks.Measures taken for water harvestingThe annual water harvesting potential from a rooftop are of 360 square meters is 6.54 lakh litres. The waterharvesting system was installed in 1987. Since the rainwater was stored in the existing sump, which usedfor storing the municipal supply the cost was negligible.Rooftop rainwater harvestingThe rooftop rainwater is diverted from the rooftop using 100 mm cast iron pipe to a Underground storagetank of 35,000 litres capacity. The tank is of 14.6m length, 1.20 metre width and 2.0 metre depth. Therainwater stored in the tank is pumped using motor and used for washing the buses.The management initially used to wash the buses manually, where around 600 to 700 litres of water isused for cleaning one bus. And also the amount of water spend depends on the efficiency of the worker.So the engineering section using the available metal scrap devised a washing system. This systemwashes the buses automatically is 12 minutes and with 150 litres of water only. They also devised aquick wash system in which around 40 litres is only used for washing the bus.ImpactBEST gets municipal supply water at the rate of Rs 30 for 1000 litre of water. In the absence of BMCwater they used to go for tankers, which is around Rs 460 for 10,000 litres. By adopting rainwaterhaveThey save annually Rs 50,000 by rainwater harvesting.2. TATA INSITITUTE OF SOCIAL SCIENCES ( TISS), CHEMBUR, MUMBAICase BackgroundThe area of the campus is about 42,500 sq m. Approximately 400 students and 250 staff resides in thecampus. In addition to this there is a floating population of 350 people, who visit the campus forseminar and workshops. There are four bore wells and three municipal water connections for thecampus.Measures taken for water harvesting

a) Rooftop rainwater harvestingThe rooftop rainwater from the Hostel building is diverted to a storage tank of 1000 litres capacity. Thistank is provided with a over flow arrangement also. The water from the tank is used for non potablepurpose through a G I pipe which is connected from the bottom of the tank.Six drums of 100 litres are positioned at various spots, within the premises to collect the rainwater thatfalls on the terrace. The drum are placed near the dinning hall near the director bungalow and at variouslocations near the sprouts. The rainwater collected in the drums are used for mobbing floor and washingutensils.b) Surface runoff water harvestingThe surface runoff near the director bungalow is diverted to a recharge pit of six feet depth near theexisting borewell. This water collected in the recharge pit helps in recharging the borewell.3.ASIAN PAINTS , BACK BAY DEPO, THE BOMBAY ELECTRIC SUPPLY AND TRANSPORT(BEST), MUMBAI.Case BackgroundThe total rooftop are of the campus is about 10,280 sq m. The main source of water for the factory is themunicipal supply. The water harvesting scheme is prepared to collect 50,000 litres per day during monsoonseason.Measures taken for water harvestingThe rooftop rainwater was filtered and stored in the existing sump and after filtration it is used for factorypurpose.The first phase of rain water harvesting was to collect the rainwater from the Paint House terrace (average23 KL/day) and collect in the old fire hydrant tank of 185 KL. The detail engineering design for connectingthe drain coming down coming down from the terrace of Paint House to a single drain line and leading tothe collection tank ( Old Fire Hydrant Tank) was made and a dual media filter was incorporated in thescheme for the filtration of collected water before use in the plant.ImpactAt the end of the monsoon season of 2002, more than 23,00,000 litres of rain water was harvested, a seasonwhen not much rains happened and the scheme was implemented in the mid of July month. The quality ofwater collected was found to be similar to that of water supplied by BMC in terms of organics andinorganics.