The document discusses rainwater harvesting techniques. It notes that rainwater harvesting is needed due to decreasing groundwater levels and increasing water demand. It then describes three main methods of rainwater harvesting: 1) collecting rainwater from rooftops and storing it in tanks, 2) collecting roof rainwater and recharging surface aquifers, and 3) harvesting surface runoff to recharge subsurface aquifers. The document provides formulas for calculating potential rainwater collection and emphasizes the importance of water conservation and planting trees to increase rainfall.