Rainwater harvesting is a method to collect rainwater from rooftops and store it for drinking, cooking, bathing and other household uses. The document estimates that a family of four in Bangalore, India could collect over 90,000 liters of rainwater per year from a 30ft by 40ft roof, meeting their annual fresh water needs. Rainwater is beneficial because it has zero total dissolved solids, is available freely in abundance as soft water.