How it Works

There are several types of cisterns for rainwater collection:

1) corrugated steel culverts installed upright in a concrete base and

2) freestanding fiberglass tanks.

Other systems include precast ferrocement tanks, plastic tanks, and underground burial tanks. These systems are most often used for irrigation with gravity feed; however, pumps and pressure tanks can be added for other uses.

General Principles
Size the capacity for 2 to 4 inches of rain, unless the system is meant for domestic use.
Create basins to direct overflow. Be sure basins can handle the full amount of water coming off the roof.
Maintain access. Keep cisterns 1 foot from buildings, keep plumbing fixtures accessible, do not plumb gutters into the lid such that it cannot be removed for maintenance.
Maintain gravity feed. We discourage burial of the foundation as it loses precious elevation used to create head (pressure) at the hose bib.
Be sure water entering tank is free of debris.
Do not use bottom 4″ of water (sludge layer) as it will clog the supply pipes.
Put the spigot where you will use it. Make it more convenient to use the rainwater than your Tucson water faucets.
Make sure your overflow is at least as large as your inflow.
Maintain a lightproof environment while venting the cistern.
Make sure mosquitoes do not have access to your water!

Sizing
Rainwater collection area x 0.6 = approx gallons per 1″ rain. Multiply this number by between 1 and 3 to get optimal cistern size.

Cistern capacity

4 ft. X 5 ft. = 469 gallons
4 ft. X 7 ft. = 657 gallons
4 ft. X 8 ft. = 751 gallons
4 ft. X 9 ft. = 845 gallons
4 ft. X 10 ft. = 939 gallons
4 ft. X 11 ft. = 1032 gallons
4 ft. X 12 ft. = 1126 gallons

5 ft. X 7 ft. = 1027 gallons
5 ft. X 8 ft. = 1174 gallons
5 ft. X 9 ft. = 1321 gallons
5 ft. X 10 ft. = 1468 gallons

Rainwater Incentives
Environmental Benefits
How to Proceed