"Raghavan realized it wasn’t reasonable to advocate a return to unpaved or undeveloped land to capture rainwater. Instead, he suggested installing a network of pipes and filters to capture rain wherever it fell — rooftops, driveways and sidewalks — and using it to replenish underground aquifers or storing it in collection tanks. He calculated that, if managed strategically, Chennai’s average annual rainfall of around 140 centimeters (55 inches) was sufficient to meet domestic water needs in the densely populated city." Learn more here.