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.
All new construction and building retrofits can be evaluated for opportunities to incorporate a rainwater harvesting system.
A general rule of thumb is $1 per gallon for the cost of cisterns, which 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.
9.2 Tank shall be placed on redwood lumber box with rebar reinforcement, filled with 6 inches of 3/8 crushed rock, well compacted. May top with 1 inch of sand or fine gravel to get smooth level surface under cistern.
DESIGN NOTES & CONSIDERATIONS:
1. 3” plastic pipe (ABS or Schedule 40 PVC) and fittings, typical where not specified.
2. Tank shall have all openings screened to prevent mosquito breeding and rodent access.
3. Tank overflow shall be directed to a rain garden or other suitable location.
4. First flush diverter kit (rain harvesting systems, or equivalent) recommended with adapters as necessary to connect to the 6” diverter pipe.
5. Once installed, checked, and tested, any exposed plastic pipe shall be painted with latex exterior house paint in a color approved by the MPUSD representative.
6. Cisterns connected to a gravity irrigation system shall be fitted with a 24V rain tank ball valve (3/4” NPT brass ball valve with motorized actuator) and connected to the existing irrigation timer system. Gravity irrigation tubing shall be drop tape with no pressure requirements.
7. All non-potable reuse system piping and hose bibs shall be labeled consistent with UPC Chp17 with “Caution: non-potable rainwater water, do not drink.”
8. Rainwater tanks shall be permanently marked with the capacity and the language: “Non-potable rainwater". Where openings are provided to allow a person to enter the tank, the opening shall be marked with the following language: “Danger-confined space.”
9. Tank shall be constructed on a level foundation to support full cistern.
9.1 Excavate topsoil at least 3 inches to create a hard level surface, pack subsoil with hand tamper or mechanical compactor.