WATER HARVESTING HISTORY

Water harvesting has been a recurrent feature throughout Indian history. Right from the Indus Valley Civilization 5000 years ago, examples of water harvesting are found in numerous forms, depending on the area and topography. The Indus Valley Civilization had excellent water harvesting and drainage systems; and wells were one of its distinguishing features. Dholavira, an ancient Harappan city dating Third Millennium BC, was situated on a sloping terrain between two storm water channels from where the city used to draw its water.

In the Manusmriti, it is mentioned that causing damage to irrigation works was considered a crime. In the Arthashastra, men were asked to build irrigation systems with natural water sources or other available sources. If one did not participate in the joint building of an irrigation work, labourers and bullocks were used as compensation for ones absence. The ownership of the resultant fish, ducks and crops or vegetables went to the king.

The channelizing of the waters of the Kaveri River reflects the ingenuity of the people, and the level of development of irrigation techniques in the pre-British era. By the 8th century itself, people had begun to tame the river by building embankments. The Chola kings built mud embankments, which were at least 125metres long. These covered the entire river system. However, a regulatory system was required to control the entry of flood waters into the delta. The Vijaynagar empire which followed the Cholas saw the building of the Grand Anicut or the regulatory structure, between AD 1390-1450.The eagerness of early rulers to build dams is also reflected in the Kutagani plates which state that the Kadamba king Ravivarman ordered tank-bunds to be constructed in villages near Mysore city (4th and 6th centuries AD).Surajkund, or the Sun Tank, in Haryana was a stepped stone tank built by King Surajpal of the Tomar Dynasty to catch and store rainwater from the Aravalis. This was later restored by Feroz Shah Tughlaq of the Tughlaq Dynasty. He also renovated Hauz-e-Ala'I, which later came to be known as Hauz Khas and was used as a reservoir from which the city got its water supply. The Mughals used their engineering skills to satisfy both practical and aesthetic needs. Canals with fountains and waterfalls were dug through and around the palaces to irrigate fruit orchards and gardens and to keep the palace cool in summers. Some British documents report that irrigation in the Beas-Sutlej doab covering Jalandhar and Kapurthala districts was almost entirely done by wells and not canals. For the sinking of a well cultivators belonging to both Hindu and Muslim communities consulted their respective religious advisors to find an auspicious date and spot. When the auspicious hour arrived, the circumference of the hole was marked. This was called tappa lagana and it was followed by a celebration.

Rain Water Harvesting for the Individual Houses

Roof top rain water can be diverted to the existing open / bore well. Along with this, rain water available in the open spaces around the building may be recharged into the ground through the following simple effective methods.

Percolation pits (Small houses)
Recharge Trench (Big houses / Apartments)
Recharge wells (Large buildings / industries)

Based on the size /area of the building and the underlying lithological nature of the formation the said methods may be used either individually or in combinations.

To enhance nature recharge of rain water avoid pavements since unpaved surfaces have more percolation rate.

Various Methods of Recharging In Individual Houses

Percolation Pit Method

Bore Well with Settlement Tank

Open Well Method with filter bed Sump

Percolation Pit with Bore Method Click for more Information :)

Components of Rooftop Rainwater Harvesting System

In domestic Rooftop Rainwater Harvesting Systems rainwater from the house roof is collected in a storage vessel or tank for use during the periods of scarcity. Usually these systems are designed to support the drinking and cooking needs of the family at the doorstep. Such a system usually comprises a roof, a storage tank and guttering to transport the water from the roof to the storage tank. In addition, a first flush system to divert the dirty water which contains roof debris collected on the roof during non-rainy periods and a filter unit to remove debris and contaminants before water enters the storage tank are also provided. Therefore, a typical rooftop Rainwater Harvesting System comprise of following components:

· Roof catchment
· Gutters
· Down pipe and first flush pipe
· Filter unit
· Storage tank
· Collection pit

Among the above components, storage tank is the most expensive and critical component. The capacity of the storage tank determines the cost of the system and reliability of the system for assured water supply. Following is the brief description of each component with a study of different materials used for each component.

Roof Catchment:
The roof of the house is used as the catchment for collecting the rainwater. The style, construction and material of the roof affect its suitability as a catchment. Roofs made of corrugated iron sheet, asbestos sheet, tiles or concrete can be utilized as such for harvesting the rainwater. But thatched roofs are not suitable as it gives some colour to water and also the water carries pieces of roof material (such as palm leaves).

Gutters:
Gutters are channels fixed to the edges of roof all around to collect and transport the rainwater from the roof to the storage tank. Gutters can be prepared in semi-circular and rectangular shapes as shown in figures. Locally available material such as plain galvanized iron sheet can be easily folded to required shapes to prepare semi-circular and rectangular gutters. Semi-circular gutters of PVC material can be readily prepared by cutting the PVC pipes into two equal semi-circular channels. Bamboo poles can also be used for making gutters if they are locally available in sufficient quantity. Use of such locally available materials reduces the overall cost of the system.

Downpipe and First Flush Pipe:
Downpipe:
Down pipe is the pipe, which carries the rainwater from the gutters to the storage tank. Down pipe is joined with the gutters at one end, and the other end is connected to the filter unit of the storage tank as shown in figure below. PVC or GI pipes of diameter 50 mm to 75 mm (2 inch to 3 inch) are commonly used for down-pipe. Bamboo can also be used wherever available in suitable size.

First Flush Pipe:
Debris, dirt and dust collect on the roofs during non-rainy periods. When the first rains arrive, this unwanted material will be washed into the storage tank. This caused contamination of water collected in the storage tank thereby rendering it unfit for drinking and cooking purposes.
Therefore, a first flush system is incorporated in the Rooftop Rainwater Harvesting Systems to dispose off the 'first flush' water so that it does not enter the tank. There are two such simple systems. One is based on a simple manually operated arrangement, whereby, the down pipe is moved away from the tank inlet and replaced again once the first flush water has been disposed.
In another simple and semi-automatic system, a separate vertical pipe is fixed to the down pipe with a valve provided below the "T" junction as shown in figure.
After the first rain is washed out through first flush pipe, the valve is closed to allow the water to enter the down pipe and reach the storage tank.

Filter Unit:
The filter unit is a container or chamber filled with filter media such as coarse sand, charcoal, coconut fibre, pebbles and gravels to remove the debris and dirt from water that enters the tank. The container is provided with a perforated bottom to allow the passage of water. The filter unit is placed over the storage tank. Commonly used filters are of two types. One is a ferrocement filter unit, which is comparatively heavy and the other is made of either aluminium or plastic bucket. The latter is readily available in market and has the advantage of ease in removing, cleaning and replacing.
Another simple way of filtering the debris and dust particles that came from the roof along with rainwater is to use a fine cloth as filter media. The cloth, in 2 or 3 layers, can be tied to the top of a bucket or vessel with perforations at the bottom.

Storage Tank:
Storage tank is used to store the water that is collected from the Rooftops. Common vessels used for small scale water storage are plastic bowls, buckets, jerry cans, clay or ceramic jars, cement jars, old oil drums etc. For storing larger quantities of water the system will usually require a bigger tank with sufficient strength and durability.

There are unlimited number of options for the construction of these tanks with respect to the shape (cylindrical, rectangular and square), the size (Capacity from 1,000 lt. to 15,000 lt. or even higher) and the material of construction (brickwork, stonework, cement bricks, ferrocement, plain cement concrete and reinforced cement concrete). For domestic water needs, taking the economy and durability of tanks into consideration, ferrocement tanks of cylindrical shape in capacities ranging between 4,000 lt. and 15,000 lt. are most suitable. Plain cement concrete and reinforced cement concrete are used for tank capacities usually more than 50,000 lt. Brick, stone, cement brick may be used for capacities ranging between 15,000 lt. to 50,000 lt.
The ferrocement tanks are usually constructed above ground level because of the advantages, such as, a) ease in finding structural problems/leaks, b) easy to maintain and clean and c) easy to draw water. It is difficult to detect the leaks and take corrective measures in case of underground tanks. Water from underground tanks cannot be drawn by gravity. Some kind of manual or power lifting devices need to be used for drawing the water. Further, in coastal areas, underground tanks are prone to water contamination due to fluctuation in groundwater table and leakage of stored water.

The storage tank is provided with a cover on the top to avoid the contamination of water from external sources. The cover will be in dome shape having a raise of about 20-30 cm. in the middle. The dome is provided with two circular openings, one for manhole and another for accommodating the filter. A lid covers the manhole avoiding exposure of stored water to the outside environment. The storage tank is provided with pipe fixtures at appropriate places to draw the water, to clean the tank and to dispose of the excess water. They are named tap or outlet, drainpipe and over flow pipe respectively. PVC or GI pipes of diameter 20 mm to 25 mm (¾ inch to 1 inch) are generally used for this purpose.

Collection Pit:
A small pit is dug in the ground, beneath the tap of the storage tank and constructed in brick masonry to make a chamber, so that a vessel could be conveniently placed beneath the tap for collecting water from the storage tank. A small hole is left at the bottom of the chamber, to allow the excess water to drain-out without stagnation. Size of collection pit shall be 60 cm x 60 cm x 60 cm.

COMPONENTS OF A RAINWATER HARVESTING SYSTEM

 Continued... 

8. Recharge structures

Rainwater may be charged into the groundwater aquifers through any suitable structures like dugwells, borewells, recharge trenches and recharge pits.

Various recharge structures are possible - some which promote the percolation of water through soil strata at shallower depth (e.g., recharge trenches, permeable pavements) whereas others conduct water to greater depths from where it joins the groundwater (e.g. recharge wells). At many locations, existing structures like wells, pits and tanks can be modified as recharge structures, eliminating the need to construct any structures afresh. Here are a few commonly used recharging methods:

1. Recharging of dugwells and abandoned tubewells.
In alluvial and hard rock areas, there are thousands of wells which have either gone dry or whose water levels have declined considerably. These can be recharged directly with rooftop run-off. Rainwater that is collected on the rooftop of the building is diverted by drainpipes to a settlement or filtration tank, from which it flows into the recharge well (borewell or dugwell).

If a tubewell is used for recharging, then the casing (outer pipe) should preferably be a slotted or perforated pipe so that more surface area is available for the water to percolate. Developing a borewell would increase its recharging capacity (developing is the process where water or air is forced into the well under pressure to loosen the soil strata surrounding the bore to make it more permeable).

If a dugwell is used for recharge, the well lining should have openings (weep-holes) at regular intervals to allow seepage of water through the sides. Dugwells should be covered to prevent mosquito breeding and entry of leaves and debris. The bottom of recharge wells should be desilted annually to maintain the intake capacity.

Providing the following elements in the system can ensure the quality of water entering the recharge wells:
1. Filter mesh at entrance point of rooftop drains
2. Settlement chamber
3. Filter bed

A settlement chamber

2. Settlement tank
Settlement tanks are used to remove silt and other floating impurities from rainwater. A settlement tank is like an ordinary storage container having provisions for inflow (bringing water from the catchment), outflow (carrying water to the recharge well) and overflow. A settlement tank can have an unpaved bottom surface to allow standing water to percolate into the soil.

In case of excess rainfall, the rate of recharge, especially of borewells, may not match the rate of rainfall. In such situations, the desilting chamber holds the excess amount of water till it is soaked up by the recharge structure. Thus, the settlement chamber acts like a buffer in the system.

Any container, (masonry or concrete underground tanks, old unused tanks, pre-fabricated PVC or ferrocement tanks) with adequate capacity of storage can be used as a settlement tank.

3. Recharging of service tubewells.
In this case the rooftop runoff is not directly led into the service tubewells, to avoid chances of contamination of groundwater. Instead rainwater is collected in a recharge well, which is a temporary storage tank (located near the service tubewell), with a borehole, which is shallower than the water table. This borehole has to be provided with a casing pipe to prevent the caving in of soil, if the strata are loose. A filter chamber comprising of sand, gravel and boulders is provided to arrest the impurities.

4. Recharge pits
A recharge pit is 1.5m to 3m wide and 2m to 3m deep. The excavated pit is lined with a brick/stone wall with openings (weep-holes) at regular intervals. The top area of the pit can be covered with a perforated cover. Design procedure is the same as that of a settlement tank.

5. Soakaways / Percolation pit

Filter materials in a soakaway

Percolation pits, one of the easiest and most effective means of harvesting rainwater, are generally not more than 60 x 60 x 60 cm pits, (designed on the basis of expected runoff as described for settlement tanks), filled with pebbles or brick jelly and river sand, covered with perforated concrete slabs.

6. Recharge trenches
A recharge trench is a continuous trench excavated in the ground and refilled with porous media like pebbles, boulders or broken bricks. A recharge trench can be 0.5 m to 1 m wide and 1 m to 1.5 m deep. The length of the recharge trench is decided as per the amount of runoff expected. The recharge trench should be periodically cleaned of accumulated debris to maintain the intake capacity. In terms of recharge rates, recharge trenches are relatively less effective since the soil strata at depth of about 1.5 metres is generally less permeable. For recharging through recharge trenches, fewer precautions have to be taken to maintain the quality of the rainfall runoff. Runoff from both paved and unpaved catchments can be tapped.

7. Recharge troughs

Source: A water harvesting manual for urban areas

To collect the runoff from paved or unpaved areas draining out of a compound, recharge troughs are commonly placed at the entrance of a residential/institutional complex.These structures are similar to recharge trenches except for the fact that the excavated portion is not filled with filter materials. In order to facilitate speedy recharge, boreholes are drilled at regular intervals in this trench. In design part, there is no need of incorporating the influence of filter materials.
This structure is capable of harvesting only a limited amount of runoff because of the limitation with regard to size.

8. Modified injection well
In this method water is not pumped into the aquifer but allowed to percolate through a filter bed, which comprises sand and gravel. A modified injection well is generally a borehole, 500 mm diameter, which is drilled to the desired depth depending upon the geological conditions, preferably 2 to 3 m below the water table in the area. Inside this hole a slotted casing pipe of 200 mm diameter is inserted. The annular space between the borehole and the pipe is filled with gravel and developed with a compressor till it gives clear water. To stop the suspended solids from entering the recharge tubewell, a filter mechanism is provided at the top.

In the news

Theme park to sort water harvesting problems

Bangalore, March 21, DH News Service:

A theme park on rainwater harvesting, inaugurated here on Monday, will give a real fillip to efforts aimed at making the City denizens aware of the importance of conserving water.

“Every drop of water is going to become expensive in Bangalore if people do not wake up to the growing water crisis in the City. It is high time the citizens understood their responsibility and use water judiciously and adopt rainwater harvesting,” according to Home and Transport Minister R Ashok. Inaugurating Sir M Visvesvarayya rainwater harvesting (RWH) theme park, one of its kind anywhere in the country, constructed by the Bangalore Water Supply and Sewerage Board (BWSSB) in Jayanagar here on Monday, the minister called upon the people of Bangalore to look beyond BWSSB supply and to start indigenous ways of water storage. Although efforts have been made to create awareness about the importance of RWH, as per BWSSB’s records, only 24,195 houses in the City have adopted the method till date out of 56,000 houses identified for the purpose. The newly constructed rainwater harvesting theme park is the first of its kind in India built over 4,636 sq metres where the entire park is dedicated to demonstrate 27 methods of installing rainwater harvesting. The park has an information centre called ‘Thunthuru’ which provides all information about the technology used in RWH. There is an auditorium with 70 seats which showcases short films about water and its conservation methods. Different equipment like pop-up filters used in RWH installation will be kept for display; list of plumbers’ names and numbers are also available. Books related to the RWH technology and answers for ‘frequently asked questions’ will be available. There will be help desks to clarify all doubts related to RWH at the theme park, questions can be asked over the phone too; once every week, an expert will advise citizens about the importance of RWH. There is an amphitheatre which will stage plays and music programmes. The theme for World Water Day has been rightly chosen as ‘Water for Cities: Responding to Urban Challenges’ for the year 2011. The government will shortly decide on the deadline to install RWH to those houses which are located on 60x40 area and all new houses which will be constructed on 30x40 area in the City.

In the news

Rainwater harvesting a must for Pune Published: Tuesday, Mar 22, 2011, 11:22 IST By Ritu Goyal Harish | Place: Pune | Agency: DNA

Pune is a water-rich city with four dams and three rivers supplying water. However, every year, as the summer sun beats down on the city, the citizens usually face water cuts which make them wake up to the reality of fast-depleting water resources. Rapid urbanisation, concretisation of surfaces, reduction in open spaces and tree cover and continuous pumping of water through borewells has resulted in a steady fall in groundwater tables across the district. According to the Groundwater Surveys and Development Authority (GSDA), of the 96 drought-prone watersheds (water resources) in the state, 16 are in Pune district. The state has 1,505 watersheds. While the Pune Municipal Corporation (PMC) relies on dams and rivers for sustained supply and spends a great deal of tax payers’ money to purify water, almost 60% of urban Maharashtra depends on groundwater for supply. Since water distribution by the PMC is inequitable with many suburban parts getting an hour or two of low pressure supply that is not enough, digging of borewells is a common phenomenon. According to a 2006 report of the GSDA, there are more than 5,200 borewells and over 1,000 open wells in Pune. This indiscriminate pumping out of groundwater has resulted in a crisis that can only be countered by recharging groundwater tables through rainwater harvesting (RWH). A state government resolution dated February 14, 2002 said that RWH must be adopted by all, including government bodies, individuals and industry to counter the problem. The PMC gives a 5% rebate on property tax for buildings that have a RWH system installed. According to a recent study, ‘Sustainable drinking water supply in Pune metropolitan region: alternative policies’ by Sanjay Rode of the Centre for Development Alternatives, Ahmedabad, the water demand for the PMC is 531.94 million litres per day (MLD). The PMC also supplies drinking water to the Pune and Khadki cantonments. The water demand of the KCB, PCB and Pune city combined brings the total demand to 558 MLD. In Pimpri Chinchwad Municipal Corporation area, the water demand is 239.32 MLD. In the rest of the Pune metropolitan region, the demand for water is 23.43 MLD. As per the recent report of the Maharashtra Pollution Control Board, Pune generates about 451 MLD sewage. For its treatment, the PMC has constructed six sewage treatment plants with a total capacity of 325 MLD. The remaining sewage is discharged untreated into the Mula and Mutha rivers. Courtesy : DNA

rainwater harvesting film

Around the world

Here is a write up directly from the UN website which basically explains the activities being carried around the world.

Singapore
Singapore, which has limited land resources and a rising demand for water, is on the lookout for alternative sources and innovative methods of harvesting water. Almost 86% of Singapore’s population lives in high-rise buildings. A light roofing is placed on the roofs to act as catchment. Collected roof water is kept in separate cisterns on the roofs for non-potable uses. A recent study of an urban residential area of about 742 ha used a model to determine the optimal storage volume of the rooftop cisterns, taking into consideration non-potable water demand and actual rainfall at 15-minute intervals. This study demonstrated an effective saving of 4% of the water used, the volume of which did not have to be pumped from the ground floor. As a result of savings in terms of water, energy costs, and deferred capital, the cost of collected roof water was calculated to be S$0.96 against the previous cost of S$1.17 per cubic meter.

A marginally larger rainwater harvesting and utilisation system exists in the Changi Airport. Rainfall from the runways and the surrounding green areas is diverted to two impounding reservoirs. One of the reservoirs is designed to balance the flows during the coincident high runoffs and incoming tides, and the other reservoir is used to collect the runoff. The water is used primarily for non-potable functions such fire-fighting drills and toilet flushing. Such collected and treated water accounts for 28 to 33% of the total water used, resulting in savings of approximately S$ 390,000 per annum.

Tokyo, Japan
In Tokyo, rainwater harvesting and utilisation is promoted to mitigate water shortages, control floods, and secure water for emergencies.

The Ryogoku Kokugikan Sumo-wrestling Arena, built in 1985 in Sumida City, is a well-known facility that utilises rainwater on a large scale. The 8,400 m2 rooftop of this arena is the catchment surface of the rainwater utilisation system. Collected rainwater is drained into a 1,000 m3 underground storage tank and used for toilet flushing and air conditioning. Sumida City Hall uses a similar system. Following the example of Kokugikan, many new public facilities have begun to introduce rainwater utilisation systems in Tokyo.

"Rojison", a simple and unique rainwater utilisation facility at the community level in Tokyo, Japan.

At the community level, a simple and unique rainwater utilisation facility, “Rojison”, has been set up by local residents in the Mukojima district of Tokyo to utilise rainwater collected from the roofs of private houses for garden watering, fire-fighting and drinking water in emergencies.

To date, about 750 private and public buildings in Tokyo have introduced rainwater collection and utilisation systems. Rainwater utilisation is now flourishing at both the public and private levels.

Berlin, Germany
In October 1998, rainwater utilization systems were introduced in Berlin as part of a large scale urban re-development, the DaimlerChrysler Potsdamer Platz, to control urban flooding, save city water and create a better micro climate. Rainwater falling on the rooftops (32,000 m²) of 19 buildings is collected and stored in a 3500 m³ rainwater basement tank. It is then used for toilet flushing, watering of green areas (including roofs with vegetative cover) and the replenishment of an artificial pond.

In another project at Belss-Luedecke-Strasse building estate in Berlin, rainwater from all roof areas (with an approximate area of 7,000 m²) is discharged into a separate public rainwater sewer and transferred into a cistern with a capacity of 160 m³, together with the runoff from streets, parking spaces and pathways (representing an area of 4,200 m²). The water is treated in several stages and used for toilet flushing as well as for garden watering. The system design ensures that the majority of the pollutants in the initial flow are flushed out of the rainwater sewer into the sanitary sewer for proper treatment in a sewage plant. It is estimated that 58% of the rainwater can be retained locally through the use of this system. Based on a 10-year simulation, the savings of potable water through the utilisation of rainwater are estimated to be about 2,430 m³ per year, thus preserving the groundwater reservoirs of Berlin by a similar estimated amount.

Both of these systems not only conserve city water, but also reduce the potential for pollutant discharges from sewerage systems into surface waters that might result from stormwater overflows. This approach to the control of non point sources of pollution is an important part of a broader strategy for the protection of surface water quality in urban areas.

Thailand

Example of the rainwater jar used in Thailand. Storing rainwater from rooftop run-off in jars is an appropriate and inexpensive means of obtaining high quality drinking water in Thailand. Prior to the introduction of jars for rainwater storage, many communities had no means of protecting drinking water from waste and mosquito infestation. The jars come in various capacities, from 100 to 3,000 litres and are equipped with lid, faucet, and drain. The most popular size is 2,000 litres, which costs 750 Baht, and holds sufficient rainwater for a six-person household during the dry season, lasting up to six months. Two approaches are used for the acquisition of water jars. The first approach involves technical assistance and training villagers on water jar fabrication. This approach is suitable for many villages, and encourages the villagers to work cooperatively. Added benefits are that this environmentally appropriate technology is easy to learn, and villagers can fabricate water jars for sale at local markets. The second approach is applicable to those villages that do not have sufficient labour for making water jars. It involves access to a revolving loan fund to assist these villages in purchasing the jars. For both approaches, ownership and self-maintenance of the water jars are important. Villagers are also trained on how to ensure a safe supply of water and how to extend the life of the jars. Initially implemented by the Population and Community Development Association (PDA) in Thailand, the demonstrated success of the rainwater jar project has encouraged the Thai government to embark on an extensive national program for rainwater harvesting.

Indonesia
In Indonesia, groundwater is becoming more scarce in large urban areas due to reduced water infiltration. The decrease of groundwater recharge in the cities is directly proportional to the increase in the pavement and roof area. In addition, high population density is has brought about high groundwater consumption. Recognising the need to alter the drainage system, the Indonesian government introduced a regulation requiring that all buildings have an infiltration well. The regulation applies to two-thirds of the territory, including the Special Province of Yogyakarta, the Capital Special Province of Jakarta, West Java and Central Java Province. It is estimated that if each house in Java and Madura had its own infiltration well, the water deficit of 53% by the year of 2000 would be reduced to 37%, which translates into a net savings of 16% through conservation.

Capiz Province, the Philippines
In the Philippines, a rainwater harvesting programme was initiated in 1989 in Capiz Province with the assistance of the Canadian International Development Research Centre (IDRC). About 500 rainwater storage tanks were constructed made of wire-framed ferro-cement, with capacities varying from 2 to 10 m³. The construction of the tanks involved building a frame of steel reinforcing bars (rebar) and wire mesh on a sturdy reinforced concrete foundation. The tanks were then plastered both inside and outside, thereby reducing their susceptibility to corrosion relative to metal storage tanks.

The rainwater harvesting programme in Capiz Province was implemented as part of an income generation initiative. Under this arrangement, loans were provided to fund the capital cost of the tanks and related agricultural operations. Loans of US$200, repayable over a three-year period, covered not only the cost of the tank but also one or more income generating activities such as the purchase and rearing of pigs, costing around US$25 each. Mature pigs can sell for up to US$90 each, providing an income opportunity for generating that could provide sufficient income to repay the loan. This type of innovative mechanism for financing rural water supplies can help avoid the requirement for water resources development subsidies.

Bangladesh
In Bangladesh, rainwater collection is seen as a viable alternative for providing safe drinking water in arsenic affected areas. Since 1997, about 1000 rainwater harvesting systems have been installed in the country, primarily in rural areas, by the NGO Forum for Drinking Water Supply & Sanitation. This Forum is the national networking and service delivery agency for NGOs, community-based organisations and the private sector concerned with the implementation of water and sanitation programmes in unserved and underserved rural and urban communities. Its primary objective is to improve access to safe, sustainable, affordable water and sanitation services and facilities in Bangladesh.

The rainwater harvesting tanks in Bangladesh vary in capacity from 500 litres to 3,200 litres, costing from Tk. 3000-Tk.8000 (US$ 50 to US$ 150). The composition and structure of the tanks also vary, and include ferro-cement tanks, brick tanks, RCC ring tanks, and sub-surface tanks.

The rainwater that is harvested is used for drinking and cooking and its acceptance as a safe, easy-to-use source of water is increasing amongst local users. Water quality testing has shown that water can be preserved for four to five months without bacterial contamination. The NGO Forum has also undertaken some recent initiatives in urban areas to promote rainwater harvesting as an alternative source of water for all household purposes.

Gansu Province, China
Gansu is one of the driest provinces in China. The annual precipitation is about 300 mm, while potential evaporation amounts to 1500-2000 mm. Surface water and groundwater is limited, thus agriculture in the province relies on rainfall and people generally suffer from inadequate supplies of drinking water.

Since the 1980s, research, demonstration and extension projects on rainwater harvesting have been carried out with very positive results. In 1995/96, the “121” Rainwater Catchment Project implemented by the Gansu Provincial Government supported farmers by building one rainwater collection field, two water storage tanks and providing one piece of land to grow cash crops. This project has proven successful in supplying drinking water for 1.3 million people and developing irrigated land for a courtyard economy. As of 2000, a total of 2,183,000 rainwater tanks had been built with a total capacity of 73.1 million m³in Gansu Province, supplying drinking water for 1.97 million people and supplementary irrigation for 236,400 ha of land.

Rainwater harvesting has become an important option for Gansu Province to supply drinking water, develop rain-fed agriculture and improve the ecosystem in dry areas. Seventeen provinces in China have since adopted the rainwater utilization technique, building 5.6 million tanks with a total capacity of 1.8 billion m³, supplying drinking water for approximately 15 million people and supplemental irrigation for 1.2 million ha of land.

Africa
Although in some parts of Africa rapid expansion of rainwater catchment systems has occurred in recent years, progress has been slower than Southeast Asia. This is due in part to the lower rainfall and its seasonal nature, the smaller number and size of impervious roofs and the higher costs of constructing catchment systems in relation to typical household incomes. The lack of availability of cement and clean graded river sand in some parts of Africa and a lack of sufficient water for construction in others, add to overall cost. Nevertheless, rainwater collection is becoming more widespread in Africa with projects currently in Botswana, Togo, Mali, Malawi, South Africa, Namibia, Zimbabwe, Mozambique, Sierra Leone and Tanzania among others. Kenya is leading the way. Since the late 1970s, many projects have emerged in different parts of Kenya, each with their own designs and implementation strategies. These projects, in combination with the efforts of local builders called “fundis” operating privately and using their own indigenous designs, have been responsible for the construction of many tens of thousands of rainwater tanks throughout the country. Where cheap, abundant, locally available building materials and appropriate construction skills and experience are absent; ferro-cement tanks have been used for both surface and sub-surface catchment.

Rainwater tanks constructed by local builders called "fundis" in Kenya.

Dar es Salaam, Tanzania
Due to inadequate piped water supplies, the University of Dar es Salaam has applied rainwater harvesting and utilisation technology to supplement the piped water supply in some of the newly built staff housing. Rainwater is collected from the hipped roof made with corrugated iron sheets and led into two “foul” tanks, each with a 70-litre capacity. After the first rain is flushed out, the foul tanks are filled up with rainwater. As the foul tanks fill up, settled water in the foul tanks flows to two underground storage tanks with a total capacity of 80,000 litres. Then, the water is pumped to a distribution tank with 400 litres capacity that is connected to the plumbing system of the house. The principles for the operation of this system are: (i) only one underground tank should be filled at a time; (ii) while one tank is being filled, water can be consumed from the other tank, (iii) rainwater should not be mixed with tap water; (iv) underground storage tanks must be cleaned thoroughly when they are empty; (v) in order to conserve water, water should only be used from one distribution tank per day.

Botswana
Thousands of roof catchment and tank systems have been constructed at a number of primary schools, health clinics and government houses throughout Botswana by the town and district councils under the Ministry of Local Government, Land and Housing (MLGLH). The original tanks were prefabricated galvanized steel tanks and brick tanks. The galvanized steel tanks have not performed well, with a short life of approximately 5 years. The brick tanks are unpopular, due to leakage caused by cracks, and high installation costs. In the early 1980s, the MLGLH replaced these tanks in some areas with 10-20 m³ ferro-cement tanks promoted by the Botswana Technology Centre. The experience with ferro-cement tanks in Botswana is mixed; some have performed very well, but some have leaked, possibly due to poor quality control.

Brazil
Over the past decade, many NGOs and grassroots organisations have focused their work on the supply of drinking water using rainwater harvesting, and the irrigation of small-scale agriculture using sub-surface impoundments. In the semi-arid tropics of the north-eastern part of Brazil, annual rainfall varies widely from 200 to 1,000 mm, with an uneven regional and seasonal rainfall pattern. People have traditionally utilised rainwater collected in hand-dug rock catchments and river bedrock catchments.

To address the problem of unreliable rural drinking water supply in north-eastern Brazil, a group of NGOs combined their efforts with government to initiate a project involving the construction of one million rainwater tanks over a five year period, with benefits to 5 million people. Most of these tanks are made of pre-cast concrete plates or wire mesh concrete.

Rainwater harvesting and utilisation is now an integrated part of educational programs for sustainable living in the semi-arid regions of Brazil. The rainwater utilisation concept is also spreading to other parts of Brazil, especially urban areas. A further example of the growing interest in rainwater harvesting and utilisation is the establishment of the Brazilian Rainwater Catchment Systems Association, which was founded in 1999 and held its 3rd Brazilian Rainwater Utilisation Symposium in the fall of 2001.

A tank made of pre-cast concrete plates.	A tank made of wire mesh concrete.

Bermuda
The island of Bermuda is located 917 km east of the North American coast. The island is 30 km long, with a width ranging from 1.5 to 3 km. The total area is 53.1 km². The elevation of most of the land mass is less than 30 m above sea level, rising to a maximum of less than 100 m. The average annual rainfall is 1,470 mm. A unique feature of Bermuda roofs is the wedge-shaped limestone “glides” which have been laid to form sloping gutters, diverting rainwater into vertical leaders and then into storage tanks. Most systems use rainwater storage tanks under buildings with electric pumps to supply piped indoor water. Storage tanks have reinforced concrete floors and roofs, and the walls are constructed of mortar-filled concrete blocks with an interior mortar application approximately 1.5 cm thick. Rainwater utilisation systems in Bermuda are regulated by a Public Health Act which requires that catchments be whitewashed by white latex paint; the paint must be free from metals that might leach into water supplies. Owners must also keep catchments, tanks, gutters, pipes, vents, and screens in good repair. Roofs are commonly repainted every two to three years and storage tanks must be cleaned at least once every six years.

St. Thomas, US Virgin Islands
St. Thomas, US Virgin Islands, is an island city which is 4.8 km wide and 19 km long. It is situated adjacent to a ridge of mountains which rise to 457 m above sea level. Annual rainfall is in the range of 1,020 to 1,520 mm. A rainwater utilisation system is a mandatory requirement for a residential building permit in St. Thomas. A single-family house must have a catchment area of 112 m2 and a storage tank with 45 m3 capacity. There are no restrictions on the types of rooftop and water collection system construction materials. Many of the homes on St. Thomas are constructed so that at least part of the roof collects rainwater and transports it to storage tanks located within or below the house. Water quality test of samples collected from the rainwater utilisation systems in St. Thomas found that contamination from faecal coliform and Hg concentration was higher than EPA water quality standards, which limits the use of this water to non-potable applications unless adequate treatment is provided.

Island of Hawaii, USA

At the U.S. National Volcano Park, on the Island of Hawaii, rainwater utilisation systems have been built to supply water for 1,000 workers and residents of the park and 10,000 visitors per day. The Park’s rainwater utilisation system includes the rooftop of a building with an area of 0.4 hectares, a ground catchment area of more than two hectares, storage tanks with two reinforced concrete water tanks with 3,800 m3 capacity each, and 18 redwood water tanks with 95 m3 capacity each. Several smaller buildings have their own rainwater utilisation systems as well. A water treatment and pumping plant was built to provide users with good quality water.

A wooden water tank in Hawaii, USA For more information :

http://www.unep.or.jp/ietc/publications/urban/urbanenv-2/9.asp