Single Family Residential Rainwater Harvesting Incentives/Rebate Program
Level 2 Project Plan
Complex (Active) Rainwater Harvesting Systems:
Collection – roof
Conveyance – direct water from catchment area to storage
Storage – aboveground or underground tank
Filter – gutter debris screen, downspout debris screen and filter, diverter, first flush, roof washer
View example of Level 2 Project Plan.
Step #1. Site Analysis:
- Assess site conditions to determine rainwater harvesting goals.
- Draw site to scale and include dimensions.
- Show direction of water flow off roof tops with arrows.
- Where are the high points/ridge lines? (Indicate with a + sign.)
- Where are the low points/outlets? (Indicate with a - sign.)
- Determine catchments.
- Identify areas that require irrigation.
- Label surface areas of hardscapes and landscapes, identified rainwater practice(s), and associated potential storage volume.
Step #2. Calculations:
- Calculate the total amount of water which could be collected from roof each year and calculate the total amount of water currently needed to meet landscaping needs each year.
- Calculate site's water budget and determine whether current site conditions will meet rainwater harvesting goals.
º Calculate monthly supply (rainfall harvest potential).
º Calculate monthly demand (plant water requirement).
º Calculate monthly storage/supplemental water.
- Calculate minimum requirement for storage (retain one-inch rainfall).
º Formula: Catchment area * 0.6 = required storage.
Step #3. Final Design:
- Use supply and demand calculations to size and locate tanks.
- Use gutters and downspouts to convey the water to the storage.
- Locate storage close to plants needing water and higher than the planted area to take advantage of gravity flow.
- Provide for distribution to all planted areas.
- Provide retention area(s) for overflow.