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Sizing rainwater cisterns depends on many variables including typical rain event, frequency of rain event, area of roof , or catchments, and intended purpose of cistern.

In Santa Fe, 1″ of rain falling on a 2000 sq.ft roof would almost fill up a 1250 gallon tank The historical averages for July and August are 2.14 and 2.43 inches, so it is highly unlikely that a cistern of this size would overflow assuming the water is pumped out to provide supplemental irrigation. The most likely storm event is 0.25 inches of rain/24 hours. (See the table in the cutsheet).

Rain barrels, and various types of plastic tanks are the least expensive cisterns. When covered with screens these are effective means of storing water. Buried concrete septic tanks are probably the next most cost effective cistern. Water from canales or downspouts can be piped to the tank using HDPE drainage pipe. Installation of a sediment trap (see drawing right) will help keep the tank clean and free of dirt, leaves and other debris.

Getting water out is slightly more complicated than from rain barrels, but can be easily accomplished with a small submersible pump connected to a garden hose. When the pump is plugged in, and there is water in the tank, you can irrigate with un-chlorinated rain water. (See drawing).