It is a technique of increasing the recharge of groundwater by storing rainwater locally, through roof water harvesting, refilling of dug wells, recharging of hand pumps, construction of percolation pits, trenches around fields and bunds or dams on small rivulets. The main objectives of rainwater harvesting are:
1. To meet the increasing demand of water.
2. To reduce the run-off which chokes the drains?
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3. To avoid the flooding of roads.
4. To raise the underground water table.
5. To reduce groundwater pollution.
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6. To reduce soils erosion.
7. Supplement domestic water needs.
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In ancient India, there was a tradition of developing a rainwater harvesting system. People knew the rainfall regimes. Rooftop rainwater harvesting was practiced to store drinking water, particularly in Rajasthan. In Bikaner and Barmer regions most of the houses have underground tanks or tankas, for storing drinking water.
The tankas were built inside the house or in the courtyard. These are connected to the sloping roofs of the houses with a pipe. The first spell of rain is used for cleaning the roofs and the pipes. The rain water thus collected is considered as the purest form of water. It is an extremely reliable source of drinking water.
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Nowadays, in western Rajasthan, the practice of rooftop rainwater harvesting is on the decline as plenty of water is readily available from the perennial Indira Gandhi Canal.
In ancient India, hydraulic structures were constructed to store water for irrigation and domestic use.
During the time of Chandragupta Maurya; dams, lakes and irrigation system were extensively built.
In the I Ith century, Bhopal lake, one of the largest artificial lakes of its time was built.
In the 14th century, the tank in Hauz Khas, Delhi was constructed by lltutmish for supplying water to Siri Fort area.
In arid regions, the agriculture fields are used to store water which can moisten the soil, like ‘khadins’ in Jaisalmer and ‘Johads’ in other parts of Rajasthan.
Tamil Nadu is the first and the only state in India which has made rooftop rainwater harvesting structures compulsory to all the houses across the state.