Rain water harvesting in semi-arid region of Rajasthan is carried out in the following ways :- 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 metres deep, 4.27 metres long and 2.44 metres 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 was stored in these underground ‘tankas’.