Rain harvesting is the process of collecting runoff water from roofs and other elevated surfaces for use at a later time. Homeowners then use the untreated water for irrigation or flushing toilets. According to the Texas Water Development Board, such water is an important source of pure, low-sodium water.
Rain harvesting is far from a new concept. People historically often diverted water from the roof of their homes into cisterns for storage. With the development of centralized water supply systems and easier ways to drill water wells, many people forget about this important source. However, in Texas and other locations where water is sometimes in short supply, the process is gaining popularity. Cities such as Frisco, Texas, offer water barrels and instructions to make water barrels to their citizens. San Diego offers rebates to citizens who install rain harvesting systems.
The amount of rainwater harvested from a roof is often substantial. Just 1 inch of rainfall produces 623 gallons of water from a 1,000 square-foot roof. The best surfaces for collecting rainwater include metal or concrete roofs. Valves to automatically divert the contaminated first flush from each storm help to protect the purity of the water. When used as a potable water supply, local codes often require additional filtration and purification.