In ancient India, along with the sophisticated hydraulic structures, there existed an extraordinary tradition of a rainwater harvesting system. People had in-depth knowledge of rainfall regimes and soil types and developed wide-ranging techniques to harvest rainwater, groundwater, river water, and floodwater in keeping with the local ecological conditions and their water needs. In hill and mountainous regions, people built diversion channels like the �guls� or �kuls� of the Western Himalayas for agriculture.

�Rooftop rainwater harvesting was commonly practiced to store drinking water, particularly in Rajasthan. In the flood plains of Bengal, people developed inundation channels to irrigate their fields. In arid and semi-arid regions, agricultural fields were converted into rain-fed storage structures that allowed the water to stand and moisten the soil like the �khadins� in Jaisalmer and �Johads� in other parts of Rajasthan

In the semi-arid and arid regions of Rajasthan, particularly in Bikaner, Phalodi and Barmer, almost all the houses traditionally had underground tanks or tankas for storing drinking water. The tanks could be as large as a big room; one household in Phalodi had a tank that was 6.1 meters deep, 4.27 meters long and 2.44 meters wide.

The tankas were part of the well-developed rooftop rainwater harvesting system and were built inside the main house or the courtyard. They were connected to the sloping roofs of the houses through a pipe. Rain falling on the rooftops would travel down the pipe and be stored in these underground
�tankas�. The first spell of rain was usually not collected as this would clean the roofs and the pipes.

The rainwater from the subsequent showers was then collected. The rainwater can be stored in the tanks till the next rainfall making it an extremely reliable source of drinking water when all other sources are dried up, particularly in the summers. Rainwater, or palar pani, as commonly referred to in these parts, is considered the purest form of natural water. Many houses constructed underground rooms adjoining the �tanka� to beat the summer heat as it would keep the room cool.

Today, in western Rajasthan, sadly the practice of rooftop rainwater harvesting is on the decline as plenty of water is available due to the perennial Rajasthan Canal, though some houses still maintain the tankas since they do not like the taste of tap water. Fortunately, in many parts of rural and urban India, rooftop rainwater harvesting is being successfully adapted to store and conserve water.

In Gendathur, a remote backward village in Mysore, Karnataka, villagers have installed, in their household�s rooftop, rainwater harvesting system to meet their water needs. Nearly 200 households have installed this system and the village has earned the rare distinction of being rich in rainwater. Rainwater harvesting system which is adapted here.

Gendathur receives annual precipitation of 1,000 mm, and with 80 percent of collection efficiency and of about 10 fillings, every house can collect and use about 50,000 liters of water annually. From the 20 houses, the net amount of rainwater harvested annually amounts to 1,00,000 liters.

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