Rainwater harvesting is the ancient practice of collecting and storing rainwater for later use.  Roof runoff is directed into a rain barrel or underground storage tank (i.e. cistern) via downspouts from eavestroughs or roof drains and used for purposes not requiring potable water (e.g. garden irrigation, outdoor/vehicle washing, toilet flushing, fire suppression).  Rainwater harvesting reduces the volume of water that enters the municipal storm sewer system during wet weather, which frees up capacity for conveyance, storage and treatment in downstream stormwater infrastructure.  It also conserves treated drinking water which provides cost savings to municipalities through reduced demand for municipally-supplied water and to property owners through lower water bills.  Rainwater is a better water source for irrigating vegetable gardens and landscaping because it does not contain residual chlorine and disinfection by-products found in municipally supplied drinking water.  To maximize the runoff reduction and water conservation benefits it is best to substantially or fully drain rain barrels and cisterns between storms.  

For more information about this technology, visit the Sustainable Technologies Evaluation Program’s Rainwater Harvesting page.