Rainwater harvesting is a method to capture and store rainwater for various uses. It is also used to recharge groundwater aquifers. It is a low-cost and eco-friendly technique for preserving every drop of water by guiding the rainwater to borewells, pits and wells. Rainwater harvesting increases water availability, checks the declining groundwater table, improves the quality of groundwater through the dilution of contaminants, like fluoride and nitrates, prevents soil erosion, and flooding and arrests saltwater intrusion in coastal areas if used to recharge aquifers.

Which state has made water harvesting structures in the houses compulsory? 

Tamil Nadu

Tamil Nadu has made water harvesting structures in houses compulsory. No building can be constructed without making structures for water harvesting.