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Urban rain water harvesting

  • 14/04/2001

The Japanese capital Tokyo receives 1,400 mm of rain in a year. But concrete prevents it from percolating into the ground. Urban flooding and acute water scarcity affected the people almost every second year. The solution to both problems lay in rainwater harvesting. Sumida City was the first ward of Tokyo to promote rainwater harvesting. Nearly 500 buildings in Tokyo have installed these systems. Sumida City has also launched a subsidies programme for encouraging rainwater utilisation. It offers subsidies up to one million yen for each rainwater project. The government is planning water conservation policies for promoting rainwater utilisation and restricting groundwater use.

Sri Lanka has a long-standing tradition of harvesting rain by using palm leaves, tree trunks and rocks. These systems are still in use, often to augment the water available from modern piped and tubewell water supply systems or where these systems do not reach. Water is captured from rooftops through a variety of gutters. Those who can afford manufactured materials like tin sheets use them as gutters. Those who can't afford these rely on natural resources like split bamboo, banana stem files and arecanut sheaths. Rainwater harvesting experiences in Anuradhapura district indicate that householders collect rainwater not because of the lack of drinking water but because of the better quality of rainwater.

The state of Hessen in Germany had to apply emergency laws in the summers of 1992 and 1993 to curtail the use of groundwater. Subsequently, a five-point programme was adopted and legal measures put in place. These included high charges for groundwater use, changes in the permission system for groundwater withdrawal, the use of legal instruments to reduce water consumption coercively and the installation of rainwater harvesting systems with the money raised from the hike in groundwater use fees. In 1998, it was estimated that 50,000 rainwater harvesting systems are being built every year in the country.

The small mountain kingdom of Nepal faces a water problem. Eighty per cent of the rainfall takes place between June-September in the land of sharp vertical gradient from 150-8,000 metres above the sea level, where most people depend on agriculture for their livelihoods. Providing safe drinking water to the entire population is difficult as 30 per cent of the rural population live in remote and isolated areas. In fact, 40 per cent of the rural population does not have access to safe drinking water and about 45,000 children below the age of five die every year because of waterborne diseases.

The Nepalese people have to trek for long distances to fetch water. This is because pumping of water in hills for irrigation is expensive. Innovative methods of water harvesting at micro-levels is the only way to solve the problem. Various government and non-governmental organisations are now engaged in developing local water harvesting systems like constructing rainwater ponds and storage tanks, undertaking watershed projects for management of rainfall and promotion of rooftop rainwater harvesting locally known as Baresiko pani thapne . A community-based rainwater harvesting scheme has been initiated by Peace Corps, Nepal, in the Ramechhap district and some similar schemes for schools in Kaski district.

In Laikipia, the Kenya Rainwater Association adopted rooftop rainwater harvesting. It began with harvesting rain in 200-litre oil drums. This grew into the construction of large 50-100 cubic metre capacity drums. This provided enough water for human and livestock needs as well as for small-scale vegetable cultivation. Runoff farming was soon introduced. Terraced agriculture, composting, afforestation and good land-use helped in increasing the efficiency of water harvesting.

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