FAO - Rooftop & Courtyard Water Harvesting - Case study 3: "Roof top rainwater harvesting stored in a polyethylene lined earth retention tank"

FAO - Rooftop & Courtyard Water Harvesting - Case study 3: "Roof top rainwater harvesting stored in a polyethylene lined earth retention tank"

The use of an earth tank lined with a polyethylene sheet to retain rainwater collected from the roof of the house.

An earth retention tank is a simple low cost structure that can be used to retain rain water from the rooftop. A hole is prepared and lined with a polyethylene sheet to prevent leakage. The top of the hole is covered with a metal lid for access. The roof of the house is fitted with a plastic guttering that captures the rainwater and funnels the water via a plastic pipe into the earth tank. The water in the earth tank then can be utilised for the irrigation of crops (especially during the hot dry summer months), sanitation, and potentially drinking water.

The population in Southern Tajikistan consists largely of subsistence farmers and are thus highly reliant upon their kitchen garden plots. As the population in the area continues to expand, the pressure on the land increases. The latter is already in a poor state, because it is becoming degraded through deforestation, overgrazing and general over exploitation. There is much precipitation during the rainy season from autumn until spring in Southern Tajikistan, but the scarcity of water from late spring to the end of autumn poses a problem with water shortages. During the rainy season, a lot of water is lost as surface runoff, this water can be saved in a retention tank to be utilised during the dry season. It can be used to water crops to help increase yields as well as crop diversity and quality. The additional water can also be used for sanitation, drinking water and watering of livestock.

For the establishment of such a retention tank several steps are needed. In preparation, a rough estimation of the potential volume of harvested rainwater needs to be calculated. Thereafter, a location for the tank needs to be selected so that expenses are minimised and it is easy to access. The establishment of ponds near big trees is not recommended, because the polyethylene layer might be punctured by the roots.

The actual steps of constructing the tank involve: (1) digging the pond, (2) plastering the inside walls with a fine soil and water mixture to smooth them, (3) lining the pond’s walls with double polyethylene layer, (4) connecting the inside polyethylene sheets with the pond coverage through a piece of cord, so that it can be taken out of the pond any time to be cleaned of sediments, (5) covering the pond with any available material such as a soil, water and straw mixture, reinforced by several poles, leaving an opening of 0.25 x 0.25m to extract water, (6) finally connecting the roof to the pond with a plastic pipe. To avoid dirty water flowing from the roof into the pond, the pipe should only be connected to the pond sometime after the rainfall has started. 

Contact person(s): Domullojonov Daler Welthungerhilfe, Temurmalik office, 77, H. Zarif street, Soviet settlement, Temurmalik district, Khatlon province, Tajikistan, +992 918 248084, daler.domullojonov@welthungerhilfe.de; dalerd@list.ru 

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