4.9 Rain Water Harvesting

Rain water harvesting has traditionally been used in environments where rainfall or other conditions limit water supply. Many areas of eastern Washington are situated in climatic zones where rain water collection systems, in the form of cisterns, may provide beneficial use.

Several of the well-documented benefits of rain water harvesting include:
  • Reduces domestic water demand.
  • CSO reduction strategy.
  • Emergency water for fire suppression.
  • Sustainable source for irrigation and non-potable uses.
  • Reduces peak runoff and allows sediment to settle.
  • Provides a water source when groundwater is unacceptable or unavailable, or it can augment limited groundwater supplies.

Most cisterns are constructed of plastic, steel, or concrete Plastic is commonly used where the cistern material can be protected from the impacts that excessive sunlight can have on warping and algae growth (see Figure 4.9.1). Plastic cisterns are lightweight, non-corrosive, and relatively inexpensive. Concrete or steel cisterns are sometimes used for aesthetic values and are often custom-designed to complement the scale and character of the structure. In other instances, a simple plastic or steel cistern may be clad with another material for greater aesthetic appeal.

Figure 4.9.1 - Polyethylene cistern
Polyethylene cistern used to meet residential non-potable water demand. Source: Innovative Water Systems, LLC