A rainwater harvesting compendium

Submitted by Hindi on Sun, 04/17/2016 - 11:25
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Water Community, Solution Exchange, UNICEF


rainwater_harvestingIndia’s water crisis has aggravated over the past few decades. Surface water is notenough to meet the needs of domestic, agricultural and industrial consumption. Theexisting river basins are either fully or over committed and ground water is overexploitedin 13 percent of the districts in India. The estimated per capita water storagecapacity is just 200 cu m per year, which is inadequate to meet the daily requirements ofIndia’s population.

In addition to quantity, the quality of water is declining because of rapid urbanisation,industrialisation and modernization of agriculture. Studies conducted by the CentralGround Water Board (CGWB) in several parts of India reveal that groundwater iscontaminated with fluoride, arsenic, nitrates and other salts, and is unfit for drinkingwithout treatment. In coastal Kerala and Gujarat, and parts of Tamil Nadu, sea wateringress has turned well water brackish.

The source of all water is rain. Lakes, water bodies, rivers, ground water are secondarysources of water. Rain water has been collected and used down the ages for irrigation,human consumption and now, by industries. Rain water harvesting is the process ofcollecting and storing rain water for future use. Its role and significance are seeing arevival today owing to the enormous pressures on limited ground and surface waterResources.

While RWH is a broad generic description in the rural context, as water collected mainlyfor agriculture purposes in dry land and tank-irrigated area, rooftop rain water harvestinghas a clearer definition as water collected from rooftops chiefly for domesticconsumption. It is estimated that about 70-80 percent of all rain that falls can beHarvested.

India’s rich tradition of rain water harvesting

India has a rich tradition of rain water harvesting. In ancient times, households andcommunities were self-sufficient in their water needs. Houses were designed to collectand store rain water; community tanks and systems of irrigation ensured the maximumuse of rain. Water structures were community-owned and managed. All of this changedwith the coming of piped water supply. With the government assuming ownership ofwater management, age-old traditions and practices of managing water by the communitywere abandoned.

The present water crisis has led to a revival in traditional methods of rain waterharvesting across India. At the same time, since the 1990s, practitioners have developednew techniques to harvest rain water. Rain as the primary source of water is beingrediscovered and harvested for multiple uses: Groundwater recharge, domestic use,drinking, irrigation.

In central and western India, the former rulers built an elaborate system of surface storagestructures for each town or fort. These collected rain water from a set of catchments andwere either stored and used in one place or channeled through the town or fort.

Step wells are India’s most unique contribution to architecture. They are called vav orvavadi in Gujarat, and baolis or bavadis in Rajasthan and northern India. The step wellsof Gujarat consist of a vertical shaft in the middle from which water is drawn. This shaftis surrounded by corridors, chambers and steps, which provide access to the well. Theywere profusely carved and served as a cool resting place in summer. Mata Bhavani’s vavat Ahmedabad, built in the eleventh century, is one of the earliest step wells, while theRani Vav (Queen’s well) at Patan, built during the late eleventh century, is the grandest.The Dada Harir’s vav at Ahmedabad, and the octagonal vav at Adalaj, are some of thefinest examples of step wells.

In 1615, during the Mughal rule, Abdul Rahim Khan built a unique water supply systemof the Burhanpur town (Madhya Pradesh). The system involved construction of long linesof underground tunnels with vertical airshafts to tap the underground water flow from thenearby Satpura hill ranges to the Tapi River lower down. The system is still functioningwell and is adequate to meet the entire water requirements of the town.The city of Hyderabad (Andhra Pradesh) has a glorious tradition of tanks built by its rulerMohammad Quli Qutub Shah in the 16th Century. The first source of water supply to thetown was the Hussain Sagar Lake built by Hussain Shah Wali in 1562. In the hills nearDaulatabad, two reservoirs were built by the Hindu Kings, in ancient times to meet thewater requirements of the city.

Many uses of rain water harvesting

Rain water is the purest form of water and therefore an excellent source of drinkingwater. It can be filtered or put in the sun in glass bottles to further disinfect it with UVrays. It does not require chlorination. Rain water does not have the arsenic and fluoridepollutants present in groundwater and hence, is good for drinking with minimal treatmentin area where groundwater is contaminated.

Rain water harvesting also helps conserve groundwater, and can be taken up as a people'smovement especially in regions where there is excessive groundwater exploitation foragricultural, domestic and industrial needs. Aquifer recharge also reduces the energyrequired to pump groundwater and therefore, impacts climate change. By extension, ithas a role to play in food security and growing value-added crops.

Rain water harvesting is especially important in India, where most rain fall isconcentrated in the four months of the monsoons, and the rest of the year is relatively dry.While some parts receive large amounts of rain over a few days, many parts of thecountry get scanty and irregular rainfall. In this context, rain water harvesting isimportant for storing water for communities in locally accessible structures.

In rural areas, most rain water harvesting structures serve more than one purpose while inurban areas, rooftop rain water harvesting is used primarily for domestic use andsupplements the municipal water supply.

Decentralized social structures help sustainable development by binding people and watertogether. Rain water harvesting systems are sensitive to local ecological demands andcommunity needs, for example, where the number of days with rainfall is short, thesystems use rain water for recharging groundwater.

Rain water for drinking and domestic use

Given its intrinsic qualities, rain water is ideal for drinking with minimal treatment. It isespecially useful where groundwater is contaminated, but also where other sources ofwater, such as from wells, hand pumps, the municipal corporation or panchayat sources,is irregular.

There are different ways to collect rain water for drinking and domestic use, dependingon where RWH is being practiced. In cities, where there is a shortage of open spaces butabundance of concrete roof areas, roof top RWH is the preferred option. These collectand store water for domestic consumption – drinking, maintaining gardens flushing andother household purposes. Apartment complexes, housing societies and high-risebuildings have developed effective models to harvest rain water.

Roofs are easier to maintain, water from rooftops is easily channeled and fit forconsumption as it does not contain bacteria and chemical impurities which may bepresent in run-off from other unpaved and paved areas. The rain water collected isfiltered and treated to make it suitable for consumption for household needs such ascleaning, washing, bathing, watering plants, sanitation. This reduces dependence onpiped water supply, used only for drinking and cooking. The excess harvested rain wateris channeled into a recharge ditch or well.

In cities, people usually depend on the municipal supply for drinking and cooking, whilethe rain water is used for other purposes, reducing dependence on, and conserving,municipal water supply.

In rural areas of Rajasthan, tankas (a round concrete rain water harvesting and storage structure) are used for collecting and storing rain water. These are circular, dish-antenna shaped structures made of concrete. The catchment is either round or rectangular depending on the space available and the collected rain water is stored in an underground tank in the centre. A variation of the tanka is found in Gujarat where households channel water from rooftops to an underground tank for storage.

A very simple method is practiced in heavy rainfall areas of Kerala and Karnataka.During the three monsoon months, drinking water needs of each house are met by asimple saree-based rain water harvesting system. All the three parts of the system –Catchment, transport and filtration of rain – comprises of a single piece of cloth. This traditional method is used in Kuttanad (Aleppy district), Kerala, where the availablewater is heavily contaminated. Families using this system boil the water before drinking.They keep this water in storage vessels and use it for drinking needs for a week. There ishardly any hesitation to drink rain water in these areas.

In Nagapattinam, Tamil Nadu, which has a severe water problem, roof water harvestingstructures have been installed in schools, temples, panchayat office, as well as 90households. House types include tiled, thatched-roof and concrete. Results post-rainsfound that families which had installed the RWH structures had enough rain water fortheir own needs. They sold the surplus at Re 1 per pot. If the roof was thatched, a tinsheet was placed over it from where a pipe conveyed water into a plastic tank afterfiltration. The water was tested and found safe for drinking.

Ooranis are surface storage structures that also used in Tamil Nadu for collecting rain water from a catchment area as well as what falls directly on it. These are designed to keep the water free from bacterial contamination, and filtration methods removesuspended impurities. The details are given in Annexure 2.

Rain water for recharge

Groundwater is lifeline of India's water sector, accounting for half of all water consumed.It can be a sustainable source only if the recharge equals or exceeds the amount of waterdrawn and this usually depends on the level of exploitation of the watershed, amount ofrainfall, and percolation efficiency. Rain water can be recharged into aquifers throughnatural or man-made structures like dug wells, borewells, recharge trenches and pits. Thequality of water used for recharge is critical as it risks polluting ground aquifers.Buildings with rain water harvesting systems must ensure garden areas are free ofchemicals such as insecticides and pesticides. In some cases, only water from the roof isused for recharge.

However, it is important to understand only excess water from the storage structure goestowards recharging aquifers. Against this background, rain water harvesting in one placeactually affects the recharge potential of an aquifer elsewhere. This is discussed in detailin the chapter on recommendations.

Rain water for irrigation

Traditionally, most agriculture in India has been rainfed, dependent on the twomonsoons. Farmers and rural communities have developed a whole host of rain waterharvesting techniques in each geographical area to suit local climatic and culturalconditions. These are described in detail in the section on rain water harvesting forirrigation in the next chapter.

Water policy and legislation

In recent years, many states and cities have mandated rain water harvesting. This is partlyas a result of the growing problem of providing an assured supply of water for allpurposes, partly to raise awareness of the need for conserving water, and partly becauseof growing public awareness that the government cannot provide for all the water needsof everybody. All states use a combination of monetary and punitive measures to‘encourage’ their citizens to set up rain water harvesting systems.

Himachal Pradesh

All commercial and institutional buildings, tourist and industrial complexes, hotels etc,existing or coming up and having a plinth area of more than 1000 square metres will haverain water storage facilities commensurate with the size of roof area. No objectioncertificates, required under different statutes, will not be issued to the owners of thebuildings - unless they produce satisfactory proof of compliance of the new law. Toiletflush systems will have to be connected with the rainwater storage tank. It has beenrecommended that the buildings will have rain water storage facility commensurate withthe size of roof in the open and set back area of the plot at the rate of 0.24 cft. Per sq m ofthe roof area.

In 2002, the Ahmedabad Urban Development Authority (AUDA) had made rainwaterharvesting mandatory for all buildings covering an area of over 1,500 square metres.According to the rule, for a cover area of over 1,500 square metres, one percolation wellis mandatory to ensure ground water recharge. For every additional 4,000 square metrescover area, another well needs to be built.

In order to conserve water and ensure ground water recharge, the Karnataka governmentin February 2009 announced that buildings, constructed in the city will have tocompulsorily adopt rain water harvesting facility. Residential sites, which exceed an areaof 2400 sq ft (40 x 60 ft), shall create rain harvesting facility according to the new law.

Port Blair
In 2007, Port Blair Municipal Council (PBMC) directed all the persons related toconstruction work to provide a proper spout or tank for the collection of rain water to beutilised for various domestic purposes other than drinking. As per the existing buildingby-laws 1999 the slab or roof of the building would have to be provided with a properspout or gutter for collection of rain water, which would be beneficial for the residents ofthe municipal area during water crisis. The PBMC had advised all the owners ofbuildings in the Municipal area to comply with the provisions within four months failingwhich action would be taken against them by the Council.

Rainwater harvesting has been made mandatory in three storied buildings (irrespective ofthe size of the rooftop area). All new water and sewer connections are provided only afterthe installation of rainwater harvesting systems.

The Kerala Municipality Building Rules, 1999 was amended by a notification datedJanuary 12, 2004 issued by the Government of Kerala to include rainwater harvestingstructures in new construction. It also specifies the amount of storage and linkage withground water recharge, and requires the occupier of the building to maintain the rainwater harvesting structure.

New Delhi
Since June 2001, the Ministry of Urban affairs and Poverty Alleviation has maderainwater harvesting mandatory in all new buildings with a roof area of more than 100 sqm and in all plots with an area of more than 1000 sq m, that are being developed. Dualpiping has to be installed to make use of the harvesting water.

The Central Ground Water Authority (CGWA) has made rainwater harvesting mandatoryin all institutions and residential colonies in notified areas (South and southwest Delhiand adjoining areas like Faridabad, Gurgaon and Ghaziabad). This is also applicable toall the buildings in notified areas that have tubewells. The deadline for this was for March31, 2002. The CGWA has also banned drilling of tubewells in notified areas in Delhi,where ground water levels have fallen substantially over the past several decades

Indore (Madhya Pradesh)
Rainwater harvesting has been made mandatory in all new buildings with an area of 250sq m or more.

A rebate of 6 per cent on property tax has been offered as an incentive for implementingrainwater harvesting systems.

Kanpur (Uttar Pradesh)
Rainwater harvesting has been made mandatory in all new buildings with an area of 1000sq m or more.

Hyderabad (Andhra Pradesh)
Rainwater harvesting has been made mandatory in all new buildings with an area of 300sq m or more.

Tentative for enforcing this deadline was June 2001.

Tamil Nadu
Through an ordinance titled Tamil Nadu Municipal Laws ordinance, 2003, dated July 19,2003, the government of Tamil Nadu has made rainwater harvesting mandatory for all thebuildings, both public and private, in the state. The deadline to construct rainwaterharvesting structures is August 31, 2003. The ordinance cautions, 'Where the rain waterharvesting structure is not provided as required, the Commissioner or any personauthorised by him in this behalf may, after giving notice to the owner or occupier of thebuilding, cause rain water harvesting structure to be provided in such building andrecover the cost of such provision along with the incidental expense thereof in the samemanner as property tax'. It also warns the citizens on disconnection of water supplyconnection provided rainwater harvesting structures are not provided.

Haryana Urban Development Authority (HUDA) has made rainwater harvestingmandatory in all new buildings irrespective of roof area.

In the notified areas in Gurgaon town and the adjoining industrial areas all the institutionsand residential colonies have been asked to adopt water harvesting by the CGWA. This isalso applicable to all the buildings in notified areas having a tubewell, deadline was forMarch 31, 2002.

The CGWA has also banned drilling of tubewells in notified areas.

The state government has made rainwater harvesting mandatory for all public andestablishments and all properties in plots covering more than 500 sq m in urban areas.

The state government has made rainwater harvesting mandatory for all buildings that arebeing constructed on plots that are more than 1,000 sq m in size.

The deadline set for this was October, 2002.

The state roads and buildings department has made rainwater harvesting mandatory forall government buildings in the state. The water will be harvested and directed topercolation wells, and from there will be also used to maintain gardens. All new buildingsneed to have rain water harvesting systems, else they will not be issued building-usepermissions.

Models for Rain water Harvesting in urban areas

In this chapter, we will examine a few models, shared by members in their responses toqueries on rain water harvesting, on rain water harvesting. We have divided the chapterby use of rain water in urban and rural areas.

RWH for Domestic Use and Recharge in Urban Areas

Several cities have included norms for rain water harvesting in municipal by-laws fornew buildings and some even require existing buildings to be retro-fitted with thesesystems. Uptake has been slow however, due largely to a lack of information on RWH,who to approach for implementing a system and the costs. People filter the harvestedwater for drinking, or store it for other domestic uses. RWH systems in parks provideenough water to irrigate them through the dry months.

Basic Principles of Rain water harvesting for drinking

In actual field conditions, the size of the collector and storage system is dictated by theavailable roof area and the rainfall. While these factors are usually fixed, somemodifications can be made in the type of roof covering to improve runoff. The waterharvested from the available roof area, therefore, is more or less fixed and has to bejudiciously used. The typical rooftop water harvesting system includes the followingElements:

Sloping roof, designed appropriately in the direction of storage and recharge. Theroofing material should be non-toxic and the surface should be smooth, hard,dense and easy to clean. It should not release material or fibre into the water. Roofpainting is not recommended since paint contains toxic substances.

There should be no trees overhanging the roof and birds should not be allowed tonest on the roofs

Gutters and/ or down pipes depending on site rainfall characteristics and roofcharacteristics. The gutter ends should be fitted with wire mesh to keep outleaves, insects and rodents

A first rain separator to divert and dispose off the first 2.5 mm of rain.

Filtering the water to remove solids and organic material

Storage tank of appropriate size with a tight fitting cover that is light proof, amanhole cover and a flushing pipe at the base. There should be a reliable andsanitary water extraction device such as a tap or handpump that obviates the needto take water out by immersing vessels. The tank should be situated such thatthere is no chance of waste water entering it

Recharging groundwater through open wells, bore wells and percolation pits. Toconvey excess water, a hygienic soak away channel should be built at wateroutlets and a screened overflow pipe should be provided.

The details of setting up a roof top rain water harvesting structure are discussed inannexure A in terms of the type of structure, quantity of water, and use of the waterharvested.

Case studies
Apartment blocks in Badlapur, Mumbai

The average rainfall in Maharashtra state is 2,000 mm annually, mostly from June toSeptember. In July 2005, rainfall reached 1,000 mm in one day, flooding almost theentire state. In Kulgaon-Badlapur, 60 km away from Mumbai, residents realized therain’s potential as a solution to their water needs. The Kulgaon-Badlapur MunicipalCorporation decided to make a strong action plan for water management, including rainwater harvesting.

The RWH system is being implemented for housing societies to enhance the groundwatertable and to provide additional water for residents. Rain gutters and pipes were used toconnect the roofs of 36 apartment buildings forming a system that captured and storedrain water. An electric pump is used to pump water back into the buildings’ taps foreveryday household use.

About 2,000 residents now get water 24 hours a day, 7 days a week from this RWHsystem. The additional water amounts to about 100 liters per person per day, more thanenough to meet washing, toileting, and other domestic water needs. It has reduced thedemand from the municipal system, which is used only for drinking and cooking. A waterfiltration plant treats water with alum and sodium hypochlorite, making it water cleanenough for bathing. A big plus of the system was reduction in groundwater withdrawals.

Badlapur’s rain water harvesting unit, which started in March 2007 directs the surpluswater into an underground “absorption pit”, and allows it to percolate through the soil torecharge the groundwater table. An over-ground storage tank with an electric pumpdraws water from the underground tank when needed. The pipeline has a header andlateral system with a float valve that operates on a hydro pneumatic system. This meansthat whenever the water level goes down for individual buildings, the storage tank’selectric pump starts automatically.

The project cost Rs.17 lakh (about US$40,000) to build, of which the MumbaiMetropolitan Region Development Authority (MMRDA) provided Rs 10 lakh as a grantand another Rs 5 lakh as a loan. The local municipality raised the rest of the cost. Eachhousehold pays Rs 2-3 a day, enough to cover maintenance costs and ensure full loanpayment within 2 years.

For more information on the project, you can contact Ram Patkar, President, Kulgaon-Badlapur Municipal Council Ram 0251 2691556; email: rampatkar@gmail.com.



Asian Paints’ High-rise Housing Society in Powai, Mumbai

To pilot the concept of total water management, corporate Asian Paints chose a high-riseco-operative housing society in Mumbai. An innovative and highly cost-effective RWHscheme was developed in 2002 taking into consideration the existing infrastructure of thebuilding. The dome structure and terrace of the building were used as catchment areas.The dome is the highest part of the 27-floor building and stands above the overhead watersupply tanks. This dome structure has been used to an advantage by making arrangementsto collect rain water and connecting it directly to the overhead tanks that provide waterfor flushing and domestic use. Since this scheme delivers water directly from the dome tothe overhead water supply tanks, there is no need to pump water. This gives a tremendousadded benefit of saving electrical power along with water.

The rest of the terrace is used to collect rain water, and taken through the existing downpipes to the underground flush water tank. These have been extended using PVC waterpipes to an underground flush water tank. The existing down spouts which were earlierjust left on the ground to join the storm water drains are now extended using PVC waterlines to the underground flush water tank.

For the Housing Society, the RWH has not only reduced fresh water intake from theBombay Municipal Corporation, it has eliminated the requirement for water tankersduring the monsoon. The cost-benefit analysis for saving water and electrical powershowed that the investment was paid back in just one monsoon.

The company also set up a total water management centre to educate citizens on theconcept of total water management, implement water conservation in buildings, showcaserainwater harvesting and provide free expertise.

For more information and assistance, please contact Jason / Rajdeep, Asian PaintsLimited Tel: 56958547 / 8000 (B), Email: proffice@asianpaints.com

Vinod Chopra, independent consultant, New Delhi

Vinod Chopra has built a RWH structure that collects water from all the rooftop areas atone point, and drains it into a single 1.5 cu m unlined pit containing layers of gravel andsand to filter out mud. As the pit is 1.5 m deep, it never overflows, allowing water topercolate into the ground. In experiments over the past four years, it has been found that1500 litres easily percolates through the pit even in peak monsoons. Using this RWHmethod an estimated 45,000 litres (150 sq m x 30 cm) is collected per year. This isassuming that 50 percent of the rainfall (30 cm of the 60 cm annual rainfall) can beCollected.

The cost of installing the RWH system was about Rs. 15,000. The cost of enhancinggroundwater below the house is about Rs 33.33 per kilolitre over a 10-year period. Incontrast, the cost of water received from the municipality is Rs 6 per kl, making thesystem “an economically unviable option”, according to the house owner. There is a discussion in the cost of water from RWHs and what municipalities provide in the nextChapter.

For more information, please contact, Vinod Chopra vinodchopra@gmail.com

Rahul Banerjee, Aarohini Trust, Indore

The rain water collection system in … house was built in and is similar to the house inDelhi (above) but the recharge mechanism is different. Five recharge bores 30 cm each indiameter were drilled 5 m into the ground and filled with layers of gravel and sand.

This system has worked very well in recharging the water from the roof withoutoverflowing. Annually, 40,000 litres of water is harvested using the same assumptions asabove for the Delhi house. However, cost of recharge is much less. The cost of pipe hasnot been included as these pipes had to be installed to drain water from the roofregardless of whether the water is used for recharging groundwater. (If this is not done,the water flows onto the street from the rooftop which is against municipal rules.) Therecharge bores cost Rs 1,000 each, thus giving a total cost of Rs 5,000. Over a ten-yearperiod the cost of recharge is Rs 12.5 per kilolitre. The Indore municipality has just takena decision to hike water rates to a commercially viable value of Rs. 16.67 per kilolitrefrom the present subsidized rate of Rs. 6.67 per kilolitre. Thus, recharge cost per kilolitreis competitive to the new commercial rate of the Indore Municipal Corporation.

Moreover, Mr Banerjee spent another Rs. 15,000 in constructing septic tanks and soakpits to treat and recharge all wastewater produced from the house into the aquifer, thussaving the municipality the cost of disposing off wastewater.

The RWH systems are well designed and have had no problem since they wereconstructed three years ago. “Thus, if actual costs are taken into account, recharging ofstorm and wastewater is a viable economic proposition and an environmentally soundmode of using scarce water,” says Mr Banerjee.

For more information you can contact Rahul Bannerjee, email: aarohini@yahoo.com,Phone: 09926791773

M M Sharma, International Agricultural Research Institute, Hyderabad

The rooftop rain water harvesting system in the house, built along with the house in 1995,collects rain water in an underground tank with a capacity of about 100,000 litres. Thehouse gets over 125,000 litres rain from the roof in a single monsoon. Since 2005, theneighbour’s roof has also been connected to the underground tank taking the collection to250,000 litres of water in a year. This water is used for drinking, cooking, bathing andwashing clothes for the whole year. The used water goes to a soak pit to replenish theAquifers.

When the house in the Sainikpuri area of Secunderabad was constructed in 1995 themunicipal water supply was not available in the colony. Since supply began in 2002, ithas been grossly inadequate. All houses need to have their own dug wells or bore wells.Most dug wells (except those in low-lying areas) have dried up in the last 10 years withthe receding water table. In 1995, the depth of the bore well was 170 feet. Since 2004, thenew houses in the colony have 6-inch diameter bore wells (unlike 4 inch as earlier) andthe depth is now 800-1100 feet.

In Mr Sharma’s house, half the water supply of the house comes from rain water and therest from municipal supply. The bore well is not used at all. The cost of RWH structurewas almost 10 percent of the total construction cost of the house when it was built, givenits size. It was designed to provide for household needs the year round, in conjunctionwith the municipal supply. Residents say costs have been recovered and now the systemgives a net savings on electricity by avoiding use of the bore-well pump of twohorsepower. The quality of water is also much better.

For more information, contact M M Sharma, email: murli.sharma@cgiar.org

Rain water harvesting by industries

Asian Paints first implemented a RWH scheme at its oldest manufacturing facility in Bhandup, Mumbai, in 2002. It was the first corporate house in Mumbai to install such asystem. The system is designed to collect 70 kilolitres of rain water per day from rooftopsduring the monsoon. In the first phase of the implementation (2002-3), a catchment areaof 2400 sq m collected 2,274 kilolitres. In the second phase (2003-4), a catchment area of5400 sq m collected 6,845 kilolitres. The criterion for selection of rooftop was its sizeand distance from the rain water collection tank.

Water consumption from outside sources has been reduced by 60 percent. Owners say thescheme pays for itself within a three-four year period. The company has replicated theRWH system at four of its other paint plants and also across its housing colonies. Thesystem has been emulated by a number of other companies including Godrej IndustriesLtd, in its factory and housing colony in Vikhroli, Mumbai.

Godrej initiated its RWH project in May-June 2003 with two pilot projects in Mumbai.The roof of one of the Godrej Industry buildings measuring 240 sq m was taken as thecatchment. Plastic pipes used as conduits carried the water to the 8,000 litre storage tankabout 15 m on the opposite side of the building. The existing pipeline letting out rainwater from the terrace was attached with a new pipe to discharge the rain water into the storage tank. The water in the tank is used for cooling purpose in the Godrej industry. A second terrace measuring 720 sq m was used to collect water and charge the existing bore well. The total cost of installing the two pilot rooftop RWH projects for the company wasRs 30,000.

Godrej has expanded its RWH initiative. In 2007-2008, 8,500 sq. m roof area wascovered and 22,500 cu m of water was collected. This has resulted in reducing waterconsumption from the municipal supply. Recharging of two borewells has also been undertaken, which resulted in improved yield and quality. The Godrej Garden Enclave, atownship of nine towers, has a dual system of water supply: Municipal supply fordomestic use; recycled and harvested rain water for flushing, washing and gardening.

Rain water harvesting in rural areas

Unlike in cities, where rooftop RWHs is the preferred method, villages have developedan array of systems. The reason is simple – India still primarily lives in her villages andpeople use local material suitable for RWH to build their systems. They tweak thesedepending on the rainfall, geography, soil and other conditions.

Unlike in cities too, rural RWH usually serve more than one purpose. It is common to seethe same structure providing water for irrigation and watering animals, while a well onthe site provides drinking water. Water standing in these surface structures also rechargesthe shallow and medium aquifers, benefitting people living several miles away as well.

Nearly all rural RWHs can be broadly classified into open and closed systems. In theopen system, the basic unit of RWH in rural areas is a surface pond with a catchmentarea. This differs slightly in construction from place to place depending on thetopography, local material available, water use and population. It is suitable for use inmost areas save for the sandy desert or coastal regions because it is cheap to make andmaintain even though the water collected needs filtration and basic disinfection to bepotable. Surface ponds work better where is medium to light rainfall (600-800 mm ofprecipitation per annum) while rooftop systems are better for places where rainfall isscarce (less than 400 mm per annum) as they are more efficient at collection and storageof water. These systems have separate collectors for water depending on the use –drinking from a well dug nearby, washing in an enclosed compound to keep out animals,water animals in an overflow trough; the excess water drains into the ground.

In closed systems, RWH systems, a cemented catchment (roof or ground level) channelswater into a tank. These are usually single-purpose systems given their cost and size.

However it is captured, rain water is better than groundwater for drinking as it containsno arsenic, fluoride, iron or pesticides which are difficult to remove even with hi-techfilters. Simple filtration and boiling makes rain water fit for consumption. Studiesconducted by IIT Delhi show bacteria die after some time in a storage tank due to nonavailability of nutrients.

Rooftop rain water harvesting is a sustainable solution to provide clean, potable water,especially in fluoride- and arsenic-affected areas in rural India. The prerequisite for thismodel is that the roof (or catchments) be made of steel sheets or some other non-porousmaterial that will allow water to flow into a collection chamber. They must be cleanedbefore the rainy season.

The techniques and principles for rooftop RWH in rural areas are similar to those inurban areas. The main difference is the type of roofing in rural areas that is either tiled or thatched in many cases. Thatched roofs can be modified for harvesting by covering all ofpart of them with plastic sheets.

People collect rain water for drinking either directly or indirectly throughout India. Oneof the better rain water harvesting structures for drinking water suitable for rural andsome urban areas are tankas, native to Rajasthan. Tankas combine the catchment andstorage into one structure that is relatively easy to make and maintain. Rain falling on thecatchment flows to the centre and enters the tank through small holes. These can beowned either by an individual or the community. Please refer to Annexure 3 for moreDetails.

In Uttarakhand, people have made rain water harvesting tanks with capacities of 7,000litres with ferrocement that collect rooftop runoff. In Kerala, there are schemes forrecharging drinking water wells using rain water to augment the supply of drinking waterin the summer.

Case studies
Rain water harvesting for drinking
Karnataka: Rain water harvesting flouride affected areas

In Karnataka, 5,400 habitations report high levels of fluoride in ground water, used fordrinking. In June 2006, the state government launched SACHETANA. Under this, the NGO BIRD-K is facilitating construction of rain water harvesting systems in 64 villagesacross four talukas and four districts which have a high level of fluoride in groundwater.The total cost of the project is Rs 14.5 crore. The project’s greatest success has been toovercome resistance to drinking rain water in this area where people were used todrinking water from wells. Recharge of aquifers is also being tried to dilute the levels offluoride in ground water.

The project has been successful because of a partnership between the government, NGOand local people. The NGO oversees design and construction, and sanctions release ofmoney to the builder of the RWHs only after it is satisfied. Part of the cost of each systemis borne by the householders, while those below the poverty line pay a smaller amount.

Approximately 20 litres per family per day is required for drinking and cooking purposes.In a year this translates to 7,300 litres of water. A roof area of 30 sq m and a climaticzone with 300 mm of rain has 9,000 litres of rain water falling on the roof. Under theSachetana project, household RWH systems are installed to collect rain water, filter in agood sand filter, and store in either an underground or over ground tank. Rain water canbe stored for a year without getting spoilt.

The rooftop rain water harvesting tanks have capacities of 5,000-10,000 litres. This wateris filtered and 20 litres per day of this fluoride-free water is provided to families fordrinking and cooking. This has received an excellent response from the community which has found a notable improvement in health over three months of drinking rainwater compared to groundwater high in flouride.

The tanks are situated underground with a robust filter. Some are located inside the housebelow the room floor or the kitchen floor and hence occupy no outside space. The wateris regularly tested for potability using the H2S strip test. Maintenance issues are resolvedwith the community. The RWH system costs about Rs 12,000 per household. Thehousehold contributes about Rs 2,000. The family uses this water only for drinking andcooking purpose.

In Bagalkot district, NGO SKG Sangha has installed 16 rain water-based drinkingsystems at government schools. The systems have slow sand bed filters with activatedcarbon in the form of wood charcoal and a sealed storage tank in brick masonry withcapacities of 1,500-3,000 litres. The savings in electricity charges to pump ground waterwill recover the cost of the units within two years and provide clean potable water tofluoride-affected areas.

Although the use of harvested water for drinking has increased in Karnataka, a great dealof interaction is needed to make it popular. Unlike in Rajasthan or Gujarat where rainwater from rooftops have traditionally been used for drinking, this is new for Karnataka.

Gujarat: Community Rain water Harvesting to Fight Salinity, Patan District

In the Saurashtra region of Kutchh, Gujarat, communities harvest enough water to lastthem six months even though rainfall is as low as 50-200 mm a year. Pravah, a state-levelnetwork of NGOs, individuals, institutes has demonstrated examples of decentralisedprogrammes in drinking water by setting up for rooftop rain water harvesting structures.

Madhutara village, Santalpur block, in the dry Patan district of Gujarat has a high degreeof salinity in ground water. Almost all villagers are suffering from fluorosis. In 2001,villagers started a community drive to solve the crisis with help from the AhmedabadbasedNGO, UTTHAN. They desilted a 3.05 km long canal through which they divertedrain water to a 300-year-old tank, lined with plastic sheets to keep the water from mixingwith the saline groundwater.

About 82,000 cubic m of silt was extracted from the tank at a cost of Rs 42 lakh, ofwhich the government gave 60 percent and the community contributed the rest as labour.They rebuilt a 12 km long bund to hold the diverted rain water. Adjacent to the tank, wasa 45 m deep recharge well fitted with special plastic pipe to carry water from the tank.

Water from the well is pumped into a storage tank near the well. A dead well nearby alsohas water now that is free from fluoride. This water is increasingly used by villagers forDrinking.

Villagers say over-extraction of groundwater over the past 20 years had caused theincrease of salinity in groundwater. While RWH initiatives have solved drinking waterproblems, providing flouride-free water for irrigation remains a concern.

Kerala: Rain water for backwashing in Kadalundi, Calicut district

In Kerala, there are over 250 open wells per square kilometer, the highest concentrationin the world. The majority of these wells had become unusable due to high saline contentand a low water table. The average life span of wells providing clean safe water is 5-6Years.

Since Kerala lies along the Arabian Sea, it is the first state in India to receive themonsoon rains that fall twice per year. The rainy season lasts nearly four months and isparticularly abundant with an annual rainfall of 3,000 mm. These rains were neverharvested which often led to flooding and run-off. As a result, the water table wasdepleted and many wells became unusable.

Backwashing provides a solution by regenerating shallow open wells by harvesting rainwater from rooftops. It does not involve any additional storage structures compared toconventional rain water harvesting units. The first rains wash off the roof tops andchannels; subsequent rain water is diverted into the well. The soft rain water mixes withthe existing water; gradually the well adjusts with the new influx of water regeneratingitself and the water table below.

In 2004, PLANET Kerala, a local NGO began working in a small village located inKadalundi, Calicut district in north Kerala where there is a serious water shortage.Twenty households volunteered to be part of a pilot project to divert water back into theirwells to replenish the water table and rejuvenate wells back into use. PLANET Keralaprovided the expertise and the households bore the cost.

The cost of this infrastructure varied: Tiled roofs (Rs 1,000-1,300), flat terraced roofs (Rs300-750), slope terraced roofs (Rs 200-1000), thatched roofs (Rs 1,000).

The practice has been proven effective in Kerala and has a huge potential for up scaling.Assuming a modest collection per household of 100,000 litres, with an average cost ofRs.1,000 and a life expectancy of 5 years, the cost of backwashing works out to Rs.3 perkl of harvested water. Even though the immediate benefits would be more apparent inregions with over 1500 mm per annum of rainfall, adoption of the practice in areashaving lower rainfall also will have a positive effect.

BOX: Rooftop Rain water Harvesting in Schools

Rooftop rain water harvesting is a viable source of drinking water for schools, as well asa means for recharging groundwater. School authorities, students and communities mustbe involved for school RWH programmes to work as they need constant maintenance andwater quality monitoring.

In Madhya Pradesh, an agency helped a tribal girls’ school implement a RWH project. InDelhi, the Government provided financial support for the construction of RWH systemsthrough its school eco-club programme. Several city schools have built these systems anduse the water for gardening.

In Uttarakhand and Himachal Pradesh, schoolchildren and teachers in 40 schoolscontributed to the creation of a rooftop RWH system. The size of the rain water storagetank is 30-40,000 litres. The system serves 400 schoolchildren and 20 teachers in eachschool. Most of the rain water is used to maintain the toilets.

In Chirawa, Rajasthan, a private school set up a rooftop RWH. Water from the large roofwas channeled into two underground cement tanks; both open at the bottom so that theaquifers also got recharged. Their combined capacity is 40,000 litres, enough to supplythe school’s needs for a few months. The water is used for everything except drinking forwhich there is the municipal water supply.

In Jharkhand, an NGO involved schoolchildren and teachers in a groundwater rechargingand rain water conservation programme. In Jhabua and Dhar, Madhya Pradesh, whererainfall was low and erratic and the fluoride had contaminated groundwater, thegovernment launched an initiative to set up RWH systems for tribal schools and hostels.

In Karnataka, a programme called Suvarnajala was launched to set up RWHs in ruralschools but it did not work out. The Karnataka State Council for Science and Technologyset up RWH systems in more than 23,000 schools across the State. A simple system thatinvolved running pipes from the school roofs to a concrete storage tank through a sandbedfilter was built in these schools. The average roof area was 147 sq m and the averagenumber of students, 118. The tank storage capacity was fixed at around 6300 litres foreach school. The project did not work because (1) The roofs did not have the requisitegradient or the flow to channel water to the pipes (2) the pipes were fixed improperly andcame off (3) the plastic used in the pipes could not withstand the weathering caused bythe sun (4) the filter beds were not located under the pipes so water flowed onto theground (5) the tanks were substandard and cracked (6) taps from the tanks were stolen sothe water poured out (7) nobody was put in charge of maintaining the systems.

Rain water harvesting for agriculture and recharge

Over the last two decades there has been a revival of minor irrigation systems that catchand store rain water, such as tanks and ponds. These serve the dual purpose of providingwater for irrigation and recharging aquifers through natural percolation. In some cases,water is channeled into deep wells, jackets wells, and purpose-dug bore wells forrecharging deeper aquifers.

High altitude regions: in Ladakh, the snow and ice melt slowly through the day and water is available in the streams only in the evening, when it is too late for irrigation. Thewater in the streams was hence led by channels to storage tanks called zing and used thenext day. In the Spiti area of Himachal Pradesh, diversion channels called kul were usedto bring the melting snows from glaciers to circular tanks, from where the water wasDistributed.

Ponds were the main source of drinking water in Jammu. Ponds in the Kandi region weredug beside rivers. During floods the river waters were diverted into them. In HimachalPradesh a temporary headwall of boulders called kuhl was constructed across a ravine to divert the waters of natural flowing streams (khud) through a canal to the fields. About 20 ha could be irrigated by a community kuhl. The water would flow from field to field and surplus water would drain back to the khud. The kohli or water tender distributed andmanaged the water.

In the eastern Himalayas, systems made from bamboo called shyngiar (in Meghalaya) or apatani (in Arunachal Pradesh) are used. Farmers harvest both ground and surface water; they block streams with a low wall and channel the water to their fields.

Kuhls – gravity-based irrigation canals in the Kangra valley of Himachal Pradesh – were built by the kings for irrigation and water supply in ancient times. Presently, the future of these kuhls is threatened as hydel projects coming up in the area ignore communityconcerns to release water into these lifelines of the villages. This has reduced or stoppedwater supply into the Kuhls.

In hilly areas: Gravity-based irrigation systems are better suited to hilly areas. Acombination of check dams, percolation tanks and field ponds are used. Small structureslike brushwood dams or gabions slow the flow of water down hillside gullies and ensuremore even distribution. Larger gabions can divert part of this into field ponds, providedthe region has enough plains to make fields. On steeper slopes, contour bunding andterrace farming where steps ‘carved’ into the hillside check the runoff can provide waterfor irrigating at least one crop.

Contour bunding is a watershed management practice to build up soil moisture storageand arrest run-off through bunds connecting equal ground elevations. A contour trench isthe reverse of the bund. Trenches are excavated at different contour levels to conserve therun off in trenches, facilitating percolation of stores water underground. In sloping/ hillyareas, these contours bunds/trenches can be inter-connected by masonry chutes to allowsmooth flow of excess run-off water from the hill tops to the hill base wherein necessaryground structures could be constructed to contain water. Use of half-moon trenches isalso useful in slope stabilization and also allowing percolation of rainfall into the ground.

Check dams reduce the velocity of rain water run-off allowing it to percolate into the soiland recharge aquifers. They raise soil moisture levels, enabling people to cultivate at leastone crop and improve water availability in wells or hand pumps. In the villages ofRalegaon Sidhi and Hiware Bazaar in Maharashtra, the Arvari river basin area ofRajasthan and several other parts of India, people have built an elaborate network ofcheck dams to arrest the flow of water, allowing it to percolate and recharge aquifers.Local materials such as mud and rocks are used to make the check dams while largerstructures are built with concrete.

Brushwood dams are the simplest kind of dam, and comprise thin long sticks tiedtogether with rope, placed across a gully between two rows of stakes planted in theground. Large boulders are put on top of the stakes to hold them place and make up therest of the dam. These are ideal for narrow gullies and hilly areas to arrest the rapid flowof water.

Gabions are ‘bags’ of rocks, 15-25 cm in size, bound together by heavy-duty galvanizedwire or nylon nets. This is a kind of check dam being commonly constructed across smallstream to conserve stream flows with practically no submergence beyond stream course.The boulders locally available are stored in a steel wire mesh and are tied up in the formof rectangular blocks. This is put up across the stream to make it as a small dam byanchoring it to the stream banks. The height of such structures is around 0.5 m and isnormally used in the streams with width of about 10 to 15 m. The excess water overflowsthis structure storing some water to serve as source of recharge. The silt content of streamwater in due course is deposited in the interstices of the boulders to make it moreimpermeable. These structures are common in Maharashtra, Madhya Pradesh, AndhraPradesh, etc. Both are extremely useful in checking the silt load in streams, the bugbearof any water management system.

In the Gangetic plain, the rivers and their floodwaters are the main source of water. Ahar-pyne is a traditional floodwater harvesting system indigenous to south Bihar. Here the terrain has a marked slope, the soil is sandy, groundwater levels are low and riversflood their banks only during the monsoon. The ahar is the catchment basin embanked onthree sides, while the fourth side is the natural slope. Pynes or artificial channels start outfrom the river, and meander through fields to end up in an ahar.

Inundation canals were an efficient irrigation system in Bengal. Floodwaters rich in siltentered the inundation canals, and were carried to the fields. The canals were broad andshallow and long and continuous. Channels cut into their sides distributed water to thefields. They were closed once the floods ceased.

In arid regions: Khadin is a land-use system in Rajasthan in which run-off from acatchment is stored in fields at lower levels behind a bund. Fields immediately behind thebund typically remain submerged during the rainy season while those at higher levelswithin the khadin have assured moisture for a rainy season crop. A second crop is grownusing the stored moisture in areas that are submerged during the rainy season. Farmersmanage to eke out a crop during the rainy season even in drought years.

In the Alwar district, Rajasthan, people revived the traditional watershed technologyJohads to restore the ecological balance of the region. These are usually crescent shaped earthen walls built across the slope of the land to catch and store rain water runoff. They usually store enough water to supply the community’s needs between monsoons and the water is put to multiple use – watering animals, domestic use, agriculture and aquiferrecharge. People use handpumps or wells situated downstream of the johad for drinkingWater.

The Bhil tribals of Jhabua district, Madhya Pradesh, have a unique water harvestingsystem which is suitable to hilly terrain. This consists of constructing a temporarydiversion weir of earth and stones on a hilly stream at the beginning of the kharif season and diverting the water into a channel parallel to the stream, but at a shallower gradient.After a few kilometers, this channel is at a considerable height from the stream bed andcan reach a farm situated on the bank of the stream to irrigate it. This system is called thepat system by the Bhils and is still being used because it is much cheaper than pump irrigation. The system is put in place and maintained with the involvement of thecommunity. In village Bhitada on the banks of the Narmada, the pat is taken to fieldsover 4 km downstream from the place where the weir is constructed.

In Bundelkhand: In this region of central India, the former Rajput rulers built enormous artificial lakes to store water from seasonal rivers. Called talaabs, these lakes were made by building a stone-and-adobe wall across a seasonal river. These held water for several seasons if the rainfall was good and supplied water for agriculture, drinking and watering animals. They were also often used for recreation by the local royalty. The talaabs were also helpful in regulating the climate in this part of India that experiences extremes of Temperature.

In south India: In Tamil Nadu, Andhra Pradesh and Karnataka, there is a complexsystem of village tanks for collecting rain water. All three states have erratic rainfall andtherefore, nearly every village has built its own tanks to maximize the collection of rainwater. The tanks provide water for irrigation, animals, and recharge drinking water wells.Tamil Nadu has 39,000 tanks; Karnataka has 30,000 and Andhra Pradesh 75,000.

Approximately one-third of the irrigated area of Tamil Nadu is watered by crescentshapedtanks called eris. Earthen walls, sometimes lined with stones, make up two-thirdsof the sides of an eri; one-third is open, facing the slope from where rain water flows in tofill it. The overflow of one eri fills the next and the next one’s overflow fills the next. Erisact as flood-control systems. They prevent soil erosion and wastage of run-off duringperiods of heavy rainfall. They recharge the groundwater in surrounding areas.

In Kasaragod district, northern Malabar region of Kerala, people depend on groundwater,and on a special water harvesting structure called surangam – a horizontal well mostly excavated in hard laterite rock formations. A surangam is about 0.45-0.7 m wide andabout 1.8-2 m high. The length varies from 3-300 m. Usually several subsidiarysurangams are excavated inside the main one.

Box: How to select a good pond site

A good pond site should possess the following traits:

1. It should be a narrow gorge with a fan shaped valley above: so that a smallamount of earthwork gives a large capacity.
2. The capacity catchment area ratio should be such that the pond can fill up in about2-3 months of rainfall. The capacity should not be too small to be choked up withsediments very soon.
3. The pond should be located where it could provide adequate drinking watersecurity throughout the year.
4. Junction of two tributary, depressions and other sites of easily available fillmaterial and favourable geology should be preferred.
5. The site should not have excessive seepage losses.
6. The catchment area should be put under conservation practices.

New techniques

In Nashik district of Maharashtra 200 farmers formed a cooperative to harness waterfrom a distant source and irrigate their fields. They have developed their own system totap and store rain water and use it during the dry months for agriculture.

In Hiware Bazar, a village in Ahmednagar district of Maharashtra, the bore blasttechnique was used to use explosive for splitting rocks on flatland. This allowed waterfrom check dams located in the hills near the village to percolate into the aquifers. Thishas resulted in village well and handpumps having sweet water.

The government has used remote sensing and aerial photo-interpretation to assess India’sground water resources since 1974. Hydromorphological maps were prepared throughaerial photo-interpretation on a 1:50,000 scale indicating the hydromorphic unit-wiseground water potential in quantitative terms. In 1978, geomorphological maps wereprepared based on visual interpretation of Landsat-1 imagery on a 1:2,50,000 scale andgeomorphic province-wise ground water potentials were evaluated taking into accountthe landform, lithology, drainage and lineament density and the ground water potentialsindicated in qualitative terms.

In the year 1984, Ground water potential maps were prepared on a 1:2,50,000 scale basedon visual interpretation of Landsat-MSS data where ground water potentials wereevaluated by combining the geology, geomorphology, terrain conditions, depth ofweathering, etc. In 1985, ground water potential maps were prepared on 1:50,000 scaleusing high resolution Landsat-TM date taking into account the lithology, landform andstructural information. Ground water potential maps were also prepared by Department ofSpace for the states of Maharashtra, Karnataka and Rajasthan by adopting a commonLegend.

The Department of Space also prepared hydro-geomorphological maps on a 1:2,50,000scale using Landsat-TM and IRS-1A/1B data for all districts. Subsequently, the NationalRemote Sensing Agency (NRSA) prepared 1:50,000 scale maps under the IntegratedMission for Sustainable Development.

The most details survey was conducted by the Rajiv Gandhi National Drinking WaterMission that engaged NRSA to prepare hydro-geomorphological or ground waterprospect maps on 1:50,000 scale using IRS-1C/1D FCC satellite imagery.

BOX The Arvari story - a river is revived

In the beginning of the 1980s the 45 km river Arvari in Alwar district, Rajasthan, wasconsidered dead and the fields surrounding it were barren while just a century before, theriver was considered as the main groundwater recharge stream for the villages on itsbanks. In the village of Bhaonta-Kolyala 30 wells were dry and only 30 percent of the221 hectares of land were cultivable. The villagers used to grow one, rain-fed, crop. In1986 the villagers through voluntary labour built a huge johad to catch the water fromsurrounding hill-slopes. Since 1986, 238 water harvesting structures, mostly johads, havebeen built in the 70 villages in the 503 sq km watershed. The effort was to catch andallow water to percolate and thus recharge the aquifer. They built check dams across eachmonsoon stream in the watershed, and treated the hill slopes to reduce run-off and soilerosion to recharge aquifers. Gradually, the Arvari River began to flow even after themonsoon period and since 1995, it has become perennial again

Today about 5 percent of the rain water is used for irrigation. This seemingly smallpercentage makes a huge difference, because the water is now available at critical stagesof plant growth. Small-scale water harvesting systems operate in a similar way, givingthe farmer a tool to supply water to the crop when it is most needed. Before the waterharvesting structures were built, the water was lacking during those critical periods andthus resulting in poor yields or crop failure.

IMPACT: Using Rain water Harvesting Systems to prevent drought, Rajkot,Gujarat

As recently as 20 years ago Rajkot, Gujarat, faced a major water crisis. The groundwatertable had receded to a depth of 250 metres. By 1985, villagers started to build check damsand tanks by using funds from the District Rural Development Authority. Now the townuses remote sensing technique and geographic information systems to locate subsurfacedykes to store water. As a result it survived the drought of 2002 and agriculturalproduction has gone up as well.

According to the sarpanch of Raj-Samadhiyala village, 20 km from Rajkot city, a decadeago, the village was declared a dry area and put under the arid zone developmentprogramme of the state government. The sarpanch who also heads the 11-member villagedevelopment committee took on the task of creating a rain water harvesting programmefor the village.

Indian Space and Research Organisation conducted a hydrogeological survey usingsatellite imagery to locate fissures in the topography with the maximum percolation ofwater. The villagers constructed 12 check dams between 1986 and 1988. Since 1998, theyhave also implemented 50 microwatershed projects. The results are phenomenal: Despitepoor rainfall in the last two years, the village has plenty of water. The annual income ofthe village is Rs 2.5 crore and they earn Rs 50 lakh from the sale of vegetables alone.Adjoining villages like Aniyala, Aili Sajadiyala and Laklapur are taking a cue from Raj-Samadhiyala.

Other success stories come from Mandlikpur, Rajkot, Gujarat which built check damsand farm ponds in 1993 to recharge about 300 wells with monsoon rain water. Throughthe drought in 2001, the village had drinking water and was able to cultivate crops in themonsoon.

Gandhigram, Kutchh, Gujarat is seeing reverse migration. Dams and nullahs are beingused to harvest rain water.

In drought-affected Mahudi, Dahod Gujarat, four days of rain was sufficient to providedrinking water security.

Conclusions and Recommendations

Rain water harvesting is an age-old approach to using the abundant rainfall over India. Itdeclined in importance once the piped water systems, tubewells and handpumps cameinto vogue in urban and rural India, respectively. Assured of a water supply independentof the rainfall, people abandoned rain water harvesting structures and the socialconstructs that held them in place.

Over the past few years, practitioners and the Central and state governments haverealized the need for RWH to supplement water supplied from surface and sub-surfacesources through municipal and panchayat sources. Implicit in this is the realization thatRWH is a good source of water for a variety of domestic and agricultural uses – drinking,washing, watering animals and cropping. It is relatively pure and abundant, free and canbe used without much treatment. Rain water is also the preferred source of drinking waterwhere ground and surface water sources are contaminated and depleted, as is happeningin many parts of India.

RWH should not be viewed in isolation. It is part of a larger process of social engineeringthat puts back the community structures needed to hold it, soil and water conservationand balancing recharge with downstream flows. It affects the overall hydrological cycleas it reduces runoff, increases recharge and soil moisture. While RWH increases thewater availability wherever it is implemented, it can affect those downstream if they livein areas that get lower rainfall and are dependent on surface and sub-surface water flows.Therefore, it is important to recognise RWH’s place in integrated water resourcesManagement.

Several states have enacted bye-laws to encourage property developers, housing coloniesand individuals to set up RWH systems. These have met with mixed success. The CentralGovernment has schemes for creating assets in villages, and a large percentage of theexpenditure goes on creating or renovating water structures in villages. Most of the workand disbursements takes place through panchayats, and therefore, the schemes work bestwhere the panchayats are strong.

Despite the numerous positives of RWH, there is no national movement for it. Severalreasons are advanced by RWH’s proponents, most blaming the government for alackadaisical attitude. However, the problems lie with both people for not taking upRWH despite government schemes and initiatives, and the government for not giving itthe importance it is due.

Several examples in this document point to another issue: that of the cost of waterobtained from RWHs as against what is supplied by the government. In many cities, thewater supplied by municipalities (when indeed it comes) is either free or heavilysubsidized. In no instance does the water tariff pay for even the cost of treating rawwater, leave along the capital cost of providing the supply. RWHs however have a realcost, usually borne by the builder, with minimal government support; therefore, the costof water obtained from RWHs is higher than what is supplied by the public utility, atleast in the short term.

The solution is to take a long-term view, where RWHs will supply water for next tonothing, reliably and of consistent quality, once they are built, for decades. They tap afree resource, otherwise going waste, put control of water resources in the hands ofcommunities and individuals, and are the only means of decentralizing water supply bymaking it available at the point of consumption. RWHs encourage water savings. On theother hand, public utilities’ supplies are irregular and of variable quality. These systemshave enormous start up costs, are centralized, not accountable to their customers andextremely wasteful; there is no sense of ownership and people waste water flowing intotheir homes through pipes.

The argument for RWH

The centralization of drinking water sources has resulted in systemic neglect of localsources such as groundwater, tanks, ponds, lakes, etc. Use of other water sources shouldbe studied and if possible, incorporated in the planning process.

RWH as one of the alternate technologies for delivering drinking water needs to beexploited further. About 10 percent of rural habitations are small, remote or in waterscarceregions where conventional ways of supplying drinking water is difficult andexpensive. Depletion of groundwater in the last few decades has led to scarcity ofdrinking water in parts of the country and quality of extracted groundwater is often poor.Therefore, developing alternate sources for drinking water become extremely important.

Community Participation

The best practices from across the country show that community leadership andcollective action have been the cornerstone of a success story as mentioned above. InHiware Bazaar village, Maharashtra, community action helped transform the villagefrom water scarce to surplus. In Alwar District, Rajasthan, Rajendra Singh, TarunBharat Sangh revived a system of five streams that feeds the Yamuna. A combination ofsocial and physical reconstruction involving the village community in reviving johads,contour bunding, soil conversation, preventing tree felling in the highlands, promotingtree plantation ensured adequate and safe drinking water for the village. A WaterParliament in the Arvari river basin with representatives from 72 villages encourages soiland water conservation, decides cropping patterns and the amount of water withdrawals.It also raises funds for maintaining water bodies that have been restored in each village.The river system has now become perennial as a result and groundwater levels have risensubstantially. Ralegaon Sidhi, Ahmednagar District, under the leadership of AnnaSaheb Hazare, became a water-surplus village from a water deficit one. This wasachieved by soil conservation, afforestation in the catchments and deepening the villagewater tank that helped recharge the village wells. People were prevented from sinkingborewells deeper than 200 feet, which not only provided adequate and safe drinkingwater, but also ensured there was enough for agriculture and dairying.

Environment magazine Down to Earth (May 2002), which tracked villages that have usedRWH to fight drought, says RWH systems are ideal for India. It adds: “But it is also clearthat RWH is not about building structures. It is about collective leadership. In all thevillages we found some critical changes. Water security was possible. But only becausevillagers took critical decisions about how to ration and prioritise scarce drinking water,which crops they should grow and which not. It was not that water was abundant andforever, but that these societies had learnt to manage their water collectively.”

The argument against RWH

One of the most important underlying values in RWH is that it is a benign technologywithout undesirable consequences. RWH initiatives are driven by the followingassumption: 1) there is a huge amount of monsoon flow, which remains un-captured andeventually ends up in the natural sinks, especially seas and oceans; 2) local water needsare too small and as such exogenous water is not needed; 3) local water harvestingsystems are always small and, therefore, cost-effective; 4) since the economic, social andenvironmental values of water are very high in water scarce regions, RWH is viable; 5)incremental structures lead to incremental benefits; and 6) being small with low waterstorage and diversion capacities, they do not pose negative consequences for downstreamUses.

These ignore a few critical parameters that govern the potential of RWHs in meetinglocal water demand. a) the hydrological regime of the region/locality; b) the reliability ofRWH, governed by the reliability of rainfall; c) the constraints imposed by localgeological settings on recharge potential; and d) the aggregate demand for water fromvarious sectors within the local area.

For runoff harvesting, rainfall has to exceed a threshold to generate runoff. The actualrunoff rates depend on the correlation between rainfall and runoff in a given basin, andthis relation weakens if there is a major change in rainfall intensity and pattern. In regionswith lower annual rainfall, rainwater harvesting as a dependable source of water is likelyto be low. Fewer rainy days also means longer dry spells and thus greater losses fromevaporation for the same region. Higher intensity of rainfall can lead to high intensity inrunoff, occurring in short durations, limiting the effective storage capacity of rainwaterharvesting systems to almost equal their actual storage size. Some studies on infiltrationshow that the rate declines to a minimum value within 4-5 days of ponding. For artificialrecharge, the storage potential of the aquifer is extremely important and is determined bythe characteristics in geological formations, and the likely depth of the dewatered zone.

In any basin, the marginal benefits from new water harvesting structures will be smallerat higher degrees of development, while the marginal cost would be higher. This isbecause in highly developed basins, it will be harder to get socially and economicallyviable sites for building water impounding structures, increasing the economic andfinancial cost of harvesting every unit of water. Therefore, the cost and economicevaluation should move from watershed to basin level. It is also important to keep inmind that the negative social and environmental effects of over-appropriation of the basin’s water resources may be borne by a community living in one part of the basin,while the benefits are accrued to a community living in another part.

Constraints in taking RWH to Scale

1. Technology is not standardized and few within the building industry have theskills to build RWH systems for different purposes.

2. The initial costs are high compared while municipal or panchayat water supply ismuch cheaper; this means the cost of harvested rain water will not be competitiveand will be a disincentive for people to install the system.

3. Financial incentives are opaque and not accompanied by a how-to. Thegovernment, responsible for the financial incentive, does not inform people whereto go for the money and how to obtain it. There are conditions and complicatedprocesses that discourage most people from setting up RWHs.

4. The biggest concern in using rain water for groundwater recharge remains thequality of the water. Most filters only remove biological matter, sediment and siltload and there are no cheap techniques available for large-scale removal offertilizer and pesticide residues in the water used for recharging. Hence, from thepoint of view of managing drinking water supplies, this is dangerous.

5. All RWH systems need maintenance to ensure that rooftops are clean, the firstflushis not stored and there are no fertiliser and pesticide residue from gardensgoing into the run-off.

6. Scaling up of RWH is best done when both individual and collective roof houseunits in a locality divert rain water to a collection system and then to a storagestructure with due care to water quality. The excess should then be allowed torecharge groundwater.

7. While setting up new structures for groundwater recharge, it is important toprotect existing groundwater recharge zones. In urban areas, river beds, floodplains, lake beds, wetlands, old tanks including temple tanks, low lying areas,open spaces, playgrounds and parks are either being filled-in or built-on or beingused as garbage dumps. Large scale paving of curbs and footpaths further preventnatural ground water seepage. It is important to identify such areas, protect andrevive them.

Policy Recommendations for RWH

Problems notwithstanding, we have seen numerous states pass laws to mandate RWH. Itis essential to view RWH as part of a larger strategy for water security, and one way thatcan provide quality water at the point of use at reasonable cost. That said, policy topromote RWH has to be community-led, as illustrated by numerous examples earlier, tobe effective and owned by the people it is intended to benefit. The government as enablerhas to provide suitable financial and technical incentives as one of the drivers. It has towork with civil society and the vast system of local governance as enablers.

A national policy for rain water harvesting should be based on the success stories ofwatershed development with the involvement of village communities in different parts ofthe country. The salient features that such a policy can incorporate are:

1. Promotion of small water harvesting structures, and the concept of small isBeautiful.
2. Focus on community-driven initiatives so the ownership rests with the localpeople rather than distant government structures.
3. Propagation of structures suitable for diverse geographic and climatic zones, thatare robust yet simple enough for local people to build and maintain.
4. Convergence of government schemes at the village and municipality levels tomake funds and technical expertise available for RWH.
5. Rooftop rain water harvesting should be mandatory to increase the amount ofavailable rain water.
6. A policy for reviving traditional water harvesting bodies in the villages should beMade
7. Regional knowledge hubs can be created to share information on local andtraditional water management practices, such as those initiated by Tarun BharatSangh, Rajasthan; Anna Hazare, Maharashtra; and the N M Sadguru Water andDevelopment Foundation in Gujarat.
8. Waste water management should be a part of the policy to complement RWH.
9. The policy should encourage region-specific plans based on agro-climaticconditions. In areas where monsoon rainfall is abundant, the aim should be togenerate awareness and increase the use of RWH systems for household,agriculture and commercial purposes.

References and further reading

A Water Harvesting Manual For Urban Areas, Case Studies from Delhi, CSE publication


Rainwater Harvesting – a Handbook for Practitioners


T H Thomas and D B Martinson; gives detailed information including required parts and approximate costs. The manual covers using rain barrels, recharge pits, directing rainwater into the sump, rainwater filters and recharge wells respectively in 5 parts.

Manual on Rooftop Rainwater Harvesting Systems in Schools
Arghyam and Rainwater Club

http://www.rainwaterclub.org/docs/MANUAL%20ON%20ROOFTOP %20RAINWATER%20HARVESTING%20SYSTEM%20FOR%20SCHOOLS.pdf

(PDF, Size: 699 KB)Provides maintenance schedule, post storage treatment procedure and precautions forrooftop rainwater harvesting systems in schools

“Backwashing” -Injection of Harvested Rainwater into Open Wells for EnablingWater Quality Improvement (from Latha Bhaskar, Consultant, Kerala)
Paper; by Planet Kerala

http://www.planetkerala.org/downloads/Backwashing_English.pdf (PDF Size: 450 KB)

Dying Wisdom: Rise, Fall and Potential of India’s Traditional Water HarvestingSystem; Fourth Citizen’s Report, Centre for Science and Environment; 1997

Rainwater Harvesting and Artificial Recharge to Ground Water: A Guide to FollowCentral Groundwater Authority, International Hydrological Programme (IHP), UnitedNations Educational, Scientific and Cultural Organization (UNESCO); September 2000


The Texas Manual on Rainwater Harvesting Manual; Texas Water DevelopmentBoard; Third Edition; 2005

http://www.twdb.state.tx.us/publications/reports/RainwaterHarvestingManual_3rdedition. pdf .

Roof Water Harvesting in India, By Dinesh Kumar; Water International, InternationalWater Resources Association; 2004

http://http://www.solutionexchangeun. net.in/environment/cr/res07080603.pdf

(Size: 64 KB).

Rainwater Harvesting and Utilization, Newsletter and Technical Publications; UnitedNations Environment Program, Division of Technology, Industry and Economics




Hosted by Centre for Science and Environment (CSE), New Delhi; Presents numerous initiatives across different agro-climatic regionsof the country, with details of community based water management initiatives


Page has some of the latest designs provided by the Centre for Science and Environment as technical expertiseto individuals and organizations interested in undertaking RWH


Provides information on water recharging experiences, including Rajkot which was successful in survivingdroughts due to its quality water management practices



Women in Karnataka use saris to harvest rain


Traditional rainwater harvesting technologies



Tel: 91-11-26066854, 26059810, 29955410, 29955781, 29956394Promoted by the National Knowledge Commission, the portal provides extensiveinformation about various environmental issues, including water recharge in India


Case Studies on Rainwater Harvesting from website Indiatogether.org . Most of thestudies pertain to Karnataka and Kerala and are by development and farming journalistShree Padre

Case study Harvesting Rainfall in Badlapur


Balisana Village: Story of Fluoride Contamination and Solution


Provides an account of a community drive to resolve the fluoride pollution experienced by the district amidstDrought.

News story on Asian Paints RWH programme

http://www.financialexpress.com/news/painting-a-gainful-picture-of-waterharvesting/ 40273/1 Financial

Express 15 February 2004


Asian Paints’ RWH in Housing Society, Powai, Mumbai

Organizations working on rain water harvesting

Department of Drinking Water Supply


IRC International Water and Sanitation Centre.


Ministry of Urban Development and Poverty Alleviation


Water Justice




United Nations International Children’s Education Fund




Water Aid, UK,


World Bank’s Water and Sanitation Programme


Water Partners International, USA,


Watershed Support Services and Activities Network (WASSAN), Hyderabad


Tamil Nadu Water and Drainage Board (TWAD),


Tarun Bharat Sangh, Rajasthan
34/46 Kiran Path, Mansarover, Jaipur – 302020; Tel.: +91-141-2391092;


Pravah C-24 B, Second Floor, Kalkaji, New Delhi 110019; Tel: +91-11-26440619/26213918/26440619;

http://mail@pravah.org; http://www.pravah.org/

Rainwater Club 264, 6th Main, 6th Block, B.E.L Layout, Vidyaranyapura, Bangalore560097; Tel.: 080-23641690/ 672790

Accelerated Rural Water Supply Programme, New Delhi

Ministry of Rural Development, Government of India, 9th Floor, Paryavarn Bhawan,CGO Complex, Lodhi Road, New Delhi 110003; Tel 91-11-24361043; Fax: 91-11-24364113;




Baif Institute for Rural Development - Karnataka (BIRD-K), Karnataka

P. B. No.3 Kamadhenu, Sharda nagar, Tiptur 572 202, Karnataka; Tel: 91-8134-250658;Fax: 91-8134-251337; birdktpr@gmail.com;


Development Alternatives, Usha Srinivasan and Ridhima Sud usrinivasan@devalt.org,rsud@devalt .org B-32, Tara Crescent, Qutab Institutional Area, New Delhi – 110016;Tel:91-11-685-1158, 696-7938; Fax: 91-11-686-6031

Action for Food Production (AFPRO), New Delhi
25/1-A Pankha Road, D-Block, Janakpuri, New Delhi 110058; Tel: +91-11-28525452/28522575/28525412; Fax: +91-11-28520343; afprodel@afpro.org;


; Contact D. K. Manavalan; Executive Director; ed@afpro.org

Water and Sanitation Management Organisation (WASMO), Gujarat3rd Floor, Jalsewa Bhavan, Sector 10-A, Gandhinagar 382010 Gujarat; Tel: +91-79-23247170/ 23247171/23237075; Fax: +91-79-23247485; wasmo@wasmo.org;


People’s Learning Centre for Water and Sanitation, UTTHAN, Gujarat C-1157, 1stFloor, Manu Raja Chamardiwala, Opp. SBS, Kaliyabhid - Bhavnagar 364002; Tel.: +91-278-2573061; plc_watsan@rediffmail.com;


Centre for Science and Environment, Green Schools Programme, Centre for Scienceand Environment (CSE), New Delhi41, Tughlakabad Institutional Area, New Delhi - 110062; Tel: +91-11-29955124; Fax:+91-11- 29955879; cse@cseindia.org;


International Rainwater Harvesting Alliance (IRHA)
Maison Internationale de l'Environnement II, Chemin de Balexert 7-9, 1219 Genève, Switzerland; Tel: 41227974157; Fax: 41227974159; secretariat@irhah2o.org;


Annexure A: Details of urban rooftop rain water harvesting system

The nature of the catchment determines the quality of rain water collected. While 70percent of water over tiled surface of a terrace can be used, only 10 percent over grassyareas can be used – the rest percolates into the ground.

Generally, run-off from paved surfaces only is used for drinking and domestic use as it isfree of bacterial contamination. Mesh filters are provided at the mouth of the drain pipe toprevent leaves and debris. A ‘first-flush’ device ensures the run-off from the first spell ofrain – which carries pollutants from air and from catchment surface – is flushed away andnot collected in the storage system.

It is important to ensure water used for recharge is free of pollutants so that it does notdamage groundwater. Run-off from grassy areas can be contaminated with pesticides andtherefore, in rural areas, runoff from threshing floors can be collected and stored in anunderground tank. The catchment areas of other surface RWH and storage systems mustbe clear of encroachments or sources of pollution. Storage systems must not be pollutedby industrial or domestic waste.

The size of the catchment area and tank should be enough to supply sufficient water forthe users during the dry period; usually in most parts of India, the tank should be largeenough to provide water to a family of 5 for up to 6 months. Assuming a full tank at thebeginning of the dry season (and knowing the average length of the dry season and theaverage water use), the volume of the tank can be calculated by the following formula:

V = (t × n × q) + et
V = Volume of tank (litres)
t = Length of the dry season (days)
n = Number of people using the tank
q = Consumption per capita per day (litres)
et = Evaporation loss during the dry period

Since evaporation from a closed storage tank is negligible, the evaporation loss (et) canbe ignored (=zero)

If, for example, 40 lpd (q) is agreed upon and a dry period of 180 days (t), a storagevolume of 36 m3 would be required for a family of 5 members (n). [V = 180 (t) × 5 (n) ×40 (q) = 36,000 litres or 36 m3]. The required catchment area (i.e. the area of the roof)can be determined by dividing the volume of the tank by the accumulated average rainfallvolume (in litres) per unit area (in m2) over the preceding wet months and multiplyingthis with the runoff coefficient, which can be set at 0.8 for galvanized iron or tiled roofs.

Experience shows that with the water storage tanks next to their houses, people usebetween 20-40 litres of water per person per day (lpd). However, this may rise in timeas people relax their water use habits because of easy access. This contrasts with amaximum of l0 lpd consumption levels under similar environments with people fetchingwater from distant sources. Together with the community/ family, a decision must be taken on how the water will be used or what affordable service level can be provided.

Rooftop water harvesting systems can provide good quality potable water if the designfeatures outlined below are taken into account.

To calculate the water available, and then design the system, you must first get therainfall data in the region for at least the preceding decade. Take the lowest figure (R, inmm) as that is the most reliable – the amount of rain will certainly exceed that in anygiven year. Given the roof area is A and a runoff coefficient (amount of runoff as percentof total rainfall) of 0.8, the amount of water available in a season is 11.2 m3 or 11,200litres. If the family uses 10 litres per capita per day (lpcd) this water will last them lover 7months. The tank size will be 3.2m (diameter) X 1.6 m (height), though it usually isbetter to make two smaller tanks. The cost of the tank depends on the material and theplace the structure is being built; the options are PVC, concrete and steel tanks.

Annexure B: Surface drinking water system based on ooranis, Tamil Nadu

In rural Tamil Nadu, ooranis have provided drinking water and are now seeing a revivalof sorts. Ooranis offer a simple rural solution to storing rain water exclusively fordrinking and can be set up anywhere given their similarity to other commonly used rainwater storage structures across India.

Ooranis are made by raising earthen walls around an area that can be square, rectangularor circular. The main components of an Oorani harvesting structure are the pond withwell dressed slopes, hard and impervious bottom, a channel leading run-off water from aspecified catchment, a filtering unit, a draw well attached to a hand pump to collectdrinking water. Ooranis are normally fenced on all the sides. There are basically seventechnical design units for an Oorani system, these are:

1. Catchment area
2. Inlet (combined grit chamber with baffle wall)
3. Oorani (storage chamber)
4. Emergency or recharge well
5. Horizontal roughing filter system
6. Draw or storage well
7. Vertical upflow fine sand filter system

The catchment area is the extent of land surface that would add to the surface runoff/ground water recharge in a sub-basin with respect to a particular stream or source. Incombination with hydrological data the surface runoff can be simulated to find out aboutthe runoff potential of the catchment. The supply channel allows the controlled drainageof sheet flow runoff from the catchment and supplies the water towards the oorani. It hasto be designed and constructed for most economical condition (trapezoidal orrectangular) by taking the maximum intensity of rainfall during a year. The suitable sizeand gradient of the channel depends on the volume of runoff from the catchment.

As inlet arrangement, silt trap and stilling basin has to be designed as per the velocity offlow in the channel, soil type and particle size. Grit chambers are required to removegravel, sand and mineral particles from the raw-water and to protect following units fromsilting and abrasion. The amount of raw-water very much depends on the size ofcatchments and the rainfall intensity. While the first is site specific, the rainfall intensitycan be evaluated from available data.

The runoff obtained from the catchment for 365 days should meet the total annual waterrequirement of the people or the total required storage capacity of the Oorani. The Ooranisystem has the capacity to store water in two different ways. Around 75 % of the storagecapacity seeps into the ground to recharge the ground water. This water can be madeaccessible by providing a recharge or emergency well in the middle of the storage tank.During dry season after the surface water dried out it can be used for drinking watersupply. The surface storage of the Oorani will provide water for about 10 month of ayear. This requires the exact calculation of the volume of water to be stored. The basicstorage equation to be followed is:

Q = D + R + E
For, Q- Volume in m3
D-Demand in m3
R-Recharge in m3
E-Evaporation in m3

After defining the volume of the storage the shape has to be chosen. Round ooranis saveas much as 20 percent in construction costs compared to the other shapes. Therecommended depth should be 5 m as it has been proven that the evaporation loss can bereduced significantly. To stabilize the sidewalls of the storage and to reduce theinfiltration capacity of the oorani it is recommended to provide a stone pavement, built inseveral steps in a slope of 1:1.5. At the bottom of the revetment a foot wall should bebuilt for stabilizing the slope.

The problem with water from ooranis is the high level of turbidity. The traditional systemprovided water without filtration. Turbidity was removed by using gypsum or seedswhich flocculated the floating impurities. With technical developments in rural areas newpollutants like artificial fertilizers, pesticides and aromatic hydrocarbons have entered thesupply chain of ooranis, requiring more sophisticated treatment. Therefore the design offilter system becomes crucial for the development of the new ooranis.

Advanced treatment systems incorporate a filter system for removal of one of thefollowing contaminants:

1. Residual organic and inorganic colloidal and suspended solids
2. Dissolved organic constituents
3. Dissolved inorganic constituents
4. Biological constituents

Depth filtration systems are the only ones competitive and suitable for ooranis. Thisinvolves removal of particulate matter by passing the water through a filter bed made upof a granular and compressible medium. The options are a slow sand filter, rapid porousand compressible medium filter, intermittent porous medium filter and recirculatingporous medium filter. The slow sand filter has proven to be the most appropriate for use.

Annexure C: Tankas as an efficient means to provide rain water

The tank is completely covered and has a manhole through which people may enter toclean it. Water is pulled out by buckets through the same manhole, though larger tankasmay have a hand pump. Tankas are designed to hold water for 7-8 months, the sizedepending on the number of users. Household tankas have capacities of around 21,000litres while community tankas can hold around 200,000 litres. The tanks are always madeof concrete, as it the catchment. Before the rains, the family or community cleans thecatchment so dirt and debris do not enter the tanka. The water is usually clean enough todrink without any treatment.

Because of the constraints of availability of large open areas around the tanka and theunit cost of treatment, a circular strip of land of 12 m width around the tanka is usuallytreated, the slope of which is kept as 3 percent i.e., a fall of 3 cm in a length of 1 m.This provides bulk of the water to fill the tanka. A tanka of about 21 cu m capacity for anindividual household should preferably be built in front of the house in an open area ofabout 10 m x 10 m size. Since the rainwater from this area will be collected in the tanka,human beings and animals should not venture into the area during the monsoon toprevent pollution of water.

For a community tanka of about 200 cu m capacity, the size of the open area should be atleast 30 m × 30 m. In both the cases the land surface should be firm and sandy with aslope of about 3 percent.

A tanka of 21 cu m capacity is usually adequate to meet the minimum drinking waterrequirements of a family of 6 persons for one year, assuming a person gets 10 litres ofwater per day. Community tankas, however, have only a supplemental role since thesecan only partially meet the requirements depending upon the size of the community andthe availability of land for constructing the tankas. Viewed in this light, the waterrequirement of the community is not necessarily a governing criterion for design of atanka scheme. Instead, conservation of available water and its proper distribution and useare of crucial importance.

Some part of the rainwater is lost due to evaporation and seepage into the ground. Thisloss varies with the amount of rainfall. For low rainfall the losses are high and for highrainfall these are low. For a 21 cu m capacity tanka, you require an area with a diameterof 3.9 m and a tank that is 3.5 m deep. The wall is cement, 150 mm thick with plaster andthe cover is a stone or RCC slab. The apron around the tanka is usually 1 m wide and 100mm thick. The tank of the tanka is 100 cm X 25 cm. there are three inlets in the tank atthe apron level, each 6X3 cm with iron bars and expanded metal. There is an opening atthe top to draw water which is 1X1 m.

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