Stormwater harvesting is the collection and storage of runoff from structures or other impervious surfaces for later use. Traditionally, rain is collected from the roof. Rain collects in gutters, directing water down downspouts and into a sort of storage tank. A rainwater collection system can meet all your household needs, from as simple as collecting rainwater in a rain barrel to as sophisticated as collecting rainwater in a large tank. Rainwater is a relatively clean and completely free source of water