Simple Rainwater Harvesting Systems
A simple water harvesting system usually consists of a catchment, a distribution system and a landscape holding area, which can be a concave or planted area with a border or earthen berm to retain water for immediate use. Gravity moves the water from the catchment (for example, the roof) to a different location. Sometimes water is caught in small containers and stored for later use. Water dripping from the edge of a roof to a planted area or a diversion channel located directly below the drip edge is an example of a simple water harvesting system.
A catchment is any area from which water can be collected, including roofs, paved areas and the soil surface. The best catchments have hard, smooth surfaces, such as concrete or metal roofing material. The amount of water harvested from a catchment depends on its size, surface texture, slope and rainfall received.
Distribution systems channel water from catchments to landscape holding areas. Examples of distribution systems include gutters and downspouts, sloped sidewalks, hillsides, street and parking lot curb cutouts and channels, ditches and swales. If gravity does not cause water to flow though your distribution system, you may need to install a small pump, gates or diverters. You may need to line earthen distribution systems with an impermeable material such as plastic to keep water from soaking into non-target areas. Complex distribution systems, discussed later, also may include pipelines.
Landscape Holding Areas
Concave depressions covered by grass or plants can store water for direct landscape use and reduction of flooding and erosion. Several such holding areas can be chained together through spillways. You can create holding areas by digging out depressions and keeping the resulting soil as a berm or by using berms, moats or soil terracing to make flat areas hold water. You should, however, be aware that digging may expose poorer quality subsoils unsuitable for landscape plants.