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Rooftop: rainwater harvesting systems in Schools

The schools for rainwater harvesting have been selected on the basis of not having any source of drinking water currently. The construction component of the programme is being implemented by the Engineering Department of the various Zilla Panchayat or the District Nirmithi Kendra.

Many schools presently do not have a reliable source of water for drinking and other purposes. The school rooftop rainwater harvesting system seeks to provide a source of water for toilet flushing, cooking, washing hands and feet before eating and after toilet use, hygiene and finally, for drinking purpose – if the water is treated well.

The amount of rainwater that can be collected depends on the rooftop area, the size of the tank and the rainfall at that place. For example, in a place where it rains 500mm and the roof area is 100sqm, the rainwater falling on the roof is 50,000 litres. Some amount of it will be absorbed by the roof and some amount will be lost in the collection process. If we assume 80% can be collected, then 40,000 litres of rainwater is available for collection.

Depending on the size of the rainwater tank and the distribution of rainfall, even a 3000-litre tank may be sufficient to collect this 40,000 litres of rainwater. We must, however, keep on using the rainwater in the tank and not wait for summer to use it. By painting an information board and keeping a small rain gauge in the school, a good school can involve students in monitoring rainfall, total rain in a year, water collected in the rainwater tank and teach them to ensure good maintenance of the system.

System Components

Roof: The existing roof is made use of to collect rainwater. Since rainwater is pure as it falls from the sky, it is necessary that the roof be kept clean for water to remain pure when it is collected. When cleaning the roof with water the first rain separator must be kept open so as not to allow the dirt to enter the filter and the tank.

PVC Gutters: The gutters of PVC collect the rainwater from the roof and transfer it to the filter. On sloping roofs, PVC gutters can pick up leaves, dust, small twigs and other organic matter. The gutters need to be cleaned regularly – at least a week. During the rainy season, the PVC gutters should be inspected and cleaned daily. The gutters are fixed to the roof or the walls with clamps. The clamps hold the gutter or pipes to the wall or the roof firmly and allow a small slope in the system to enable water to flow in one direction. At all times, the PVC gutters or pipes should slope in the direction of the storage tank and not away from it. The PVC gutters should always have an end cap at the end where rainwater begins to flow in the direction of the tank.

Downpipes: PVC down pipes bring the water from the rainwater gutters or pipes vertically down. They should invariably be clamped firmly to the wall and should never be loosely fixed. The down pipe should always be firmly fixed and if necessary, the clamp should be replaced or tightend whenever necessary.

First rain separator: The first rain separator, or a washout pipe as it is called, has a valve or an end cap to allow the first little amount of rainwater to be collected separately. This has most of the dust and dirt in it. The first rain separator is also used when the roof is being cleaned or when rainwater is not to be collected. It is important to ensure that the first rain separator is always kept in the closed position and never left open. After every rain, it should be opened carefully and the waste water allowed to flow out. The pipe should then be cleaned and the valve or the end cap, closed. Sometimes the first rain separator can get jammed due to the dirt or dust in it. In such a situation the valve or the end cap should be carefully replaced by a good plumber.

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