A rainwater harvesting compendium

Author:Nitya Jacob, Resource Person & Sunetra Lala
Source: 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