The most common sizes of water cisterns for residential use hold between 5,000 and 50,000 gallons. The size needed should reflect 25 percent of the estimated water use for one year, based on an average of between 50 and 75 gallons a day per person.
In areas with cold winters, cisterns are underground, but in warmer climates, they might sit above ground. A cistern is connected to a home's gutter system, on the down slope. Gravity moves the water through a roof washer and into the cistern. Another screened intake cleans the water as it moves from cistern to the house water supply. An additional intake pipe allows a water service company to fill it if needed.