Rainwater harvesting or rain capture is the process of collecting and storing rainwater so that it can be used at a later date using existing gutter downspouts.  Once collected the rain is filtered and stored in above or below ground tanks (cistern) and used for a variety of uses.  Irrigation, topping off a pool, pressure washing vehicles, and other residential and commercial applications and non-potable uses.  (potable uses with a different filtration system)