A cistern is a receptacle built to catch and store rainwater for irrigation during dryer periods. While they are similar to
rain barrels in purpose, cisterns are usually much larger. Cisterns may be located underground, at ground level, or on
elevated stands. It is recommended that they be watertight, have smooth interior surfaces, enclosed lids, and be large
enough to provide adequate storage. They also should be fabricated from non-reactive materials such as reinforced
concrete, galvanized steel, and plastic.
Requirements for credit
Installing a cistern can result in a savings of $6.35 per quarter. Only one credit can be taken for utilizing a rain garden, dry well or cistern.
At least 50% of your property’s roof area should drain to the cistern OR the cistern must capture runoff from
impervious area on your property that is equal to 50% of your roof area.
66 cubic feet OR
500 gallons of capacity
The cistern must be completely drained in no less than 24 hours and no longer than 48 hours after each rainfall
event. Rainwater from the cistern must be applied to on-site vegetation and should not discharge from the
property. Longer drainage periods may be acceptable if the cistern is larger than the minimum sized required
The cistern must be equipped with screens, seals, or other suitable methods to prevent mosquitoes from entering
Cisterns must be equipped with an overflow or bypass device to divert runoff in excess of the cistern capacity to
the storm drainage system without causing erosion and/or property damage.
Above ground cisterns
Above ground cisterns have various capacities and can be made out of different material. About
1/4 of the roof area drains rainwater into each of the cisterns. The image to the right is an example of a simple above ground cistern designed to take water runoff from a roof.
Below ground cisterns
Excavate the hole to the required dimensions. This is usually done with a back hoe. For
example, 8 feet by 12 feet and 8 feet deep. Make sure the hole is dug to the dimensions you desire
or your storage will be seriously compromised.
Pour the cistern floor. First form up the floor of the cistern much as you would a
sidewalk, driveway or other flat work. Construct a rectangular framework from 2 x 4's and
secure it with 2 x 4 stakes driven into the ground at intervals of about 2 feet.
Form the cistern walls. The cistern walls should be constructed by first building the
outside forms and then installing #6 rebar wired together on an approximate 1 foot grid. Set
the grid into the holes bored into the concrete floor of the cistern with a hammer drill. With
the reinforcing grid in place build the inside forms. Make sure the walls are adequately
braced and then pour the concrete.
Let the concrete set for the required time period recommended by the manufacturer and
then remove the forms.
Seal the inside of the cistern, a Portland-based product with a latex additive is
recommended, possibly Damtite, or another acceptable alternative available at your local
building supply store.
Create the lid and hatches. The lid can be made of any acceptable material but should fit
snuggly to keep potential pest from entering.
Planning and Development Services
- A storm water management plan is required for residential construction projects with 200 plus square feet of impervious surfaces. Consult our residential stormwater code requirements site
for more information about the code and to download an impervious area worksheet that will help you determine if your project will require storm water management as part of the grading permit application process.