A cistern is a tank (usually underground) for storing
hauled water and/or rain water which has been collected from a roof
or other catchment area. Cistern water must have continuous
chlorination for domestic water potable use.
A floating intake takes water from a cistern below any floating scum and above any dirt that has settled to the bottom.
Size a cistern to provide service during extended periods of low rainfall. A 3-month's water supply (1/4 of the annual yield of the catchment area) is usually adequate, but install a larger cistern where rainfall is poorly distributed throughout the year.
Good cisterns are watertight and have smooth interior surfaces. Reinforced concrete, steel, and plastic are common materials. Concrete block cisterns are hard to keep watertight.
Tightly fitted covers keep out animals, dust, surface water, insects, and light. Project a watertight curb at least 6 inches past the opening to the cistern, and the cover should overlap the curb and project downward at least 2 inches.
Supply good screens on inlet, outlet, and waste pipes, and do not interconnect cistern drains with waste or sewer lines.
After construction or any maintenance, flush the cistern to remove any
sediment, brush the inside surfaces, and thoroughly disinfect.
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