Rainwater Harvesting

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

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.

Rainwater Harvesting Manual

AgriLife Rainwater Harvesting

2 Responses to Rainwater Harvesting

  1. Claud Singer says:

    I am looking for the formula to figure the amount of roof surface that produces runoff for a rain barrel.

    • bs-watson says:

      Simple estimate
      To make a simple estimate of the number of gallons
      that can be harvested from a given catchment area during a rainfall
      event, multiply the catchment area (in square feet) by the depth of a rainfall in (inches) and by a conversion factor of 0.623.

      For more information consult: http://www.agrilifebookstore.org/

      B-6240: Rainwater Harvesting: System Planning

      Price: $48.50

      Author Email: mukhtar@tamu.edu

      This manual was created to help contractors, consultants, land owners, and others plan rainwater harvesting systems. It addresses catchments that are less than 50,000 square feet and can store less than 100,000 gallons. It covers all aspects of planning, installing, operating and maintaining such systems, as well as the distribution of water for landscapes, pets, wildlife, livestock, and private potable and nonpotable in-home rainwater systems. This 2012 edition contains a chapter on cold weather considerations and underground storage. (228 pp.) By: Billy Kniffen, Brent Clayton, Douglas Kingman, Fouad Jaber

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