Rainwater Tanks

In California, rainwater may be collected from rooftops or other above ground hard or impervious structures.

Rainwater Harvesting

Rainwater includes precipitation collected from roof surfaces or other man-made aboveground collection surfaces. Cisterns are containers of various sizes that store runoff from building downspouts. Rain barrels, and larger rain tanks, are generally smaller structures, located above ground. Cisterns are larger, can be buried underground, and may be connected to the building’s plumbing or irrigation system. Rain tanks and cisterns may be used to store and release water for landscape irrigation or for domestic purposes.

OPPORTUNITIES

All new construction and building retrofits can be evaluated for opportunities to incorporate a rainwater harvesting system.

COSTS

As a general estimate, most rain tanks cost roughly a dollar per gallon of storage capacity. This does not include additional costs for shipping, installation, and plumbing which can vary based on design, material, brand and supplier. Design costs typically represent 10- 15% of the construction cost.

WHY USE RAINWATER?

Not only is rainwater 'free', it also allows us to minimize the impact of groundwater and reservoir use. With proper design and plant selection we can slow our need for potable water coming from the ground and reservoirs.

DESIGN NOTES & CONSIDERATIONS:

1. Build a sound, level foundation that can support the full cistern. Water is heavy! To do this, excavate topsoil at least 3 inches to create a hard level surface and pack down subsoil with hand tamper or mechanical compactor.  Well designed foundations can also include stone, gravel, concrete and rot-resistant wood like Redwood.

2. Size pipes appropriately. For a large collection area you will likely want a 3" PVC schedule 40 pipe. Overflow pipes should be as big as inflow pipes to prevent problems.

3. Install a First flush diverter kit (rain harvesting systems, or equivalent) with adapters as necessary. This sends all of the first drops of rain and the dust, bird droppings, and other debris they carry, away from the tank.

4. Send all over flow from the tank to a rain garden or another stormwater friendly location.

5. Screen all openings to prevent mosquito breeding and rodent access.

6. Paint all exposed plastic pipe with latex exterior house paint once it has been installed, checked, and tested.

7. Rain tanks can be connected to irrigation systems with minimal fuss. Consider using a gravity-fed irrigation system to save energy.

8. By law, all non-potable reuse system piping and hose bibs  must be labeled “Caution: non-potable rainwater water, do not drink.” (according to the universal plumbing code chapter 17).