How much rainwater and greywater can you harvest at your home? Just fill in the five input fields and the calculator will show your rainwater harvesting potential in the following chart. Input What is your roof area (in square feet)? * Your roof area can be simply calculated by multiplying the length x width of your house. What is your landscape area (patio and planting areas in square feet)? * How many persons live full time in your home? * What is your January total water use (from your water bill in gallons)? * If your monthly use is measured in CCF, then multiply your monthly use by 748 gallons per CCF. (Example: 2 CCF * 748 gal/CCF = 1,496 gallons) What is your July total water use (from your water bill in gallons)? * If your monthly use is measured in CCF, then multiply your monthly use by 748 gallons per CCF. (Example: 10 CCF * 748 gal/CCF = 7,480 gallons) OutputSupply 1" rainfall supply from roof is (gallons) Roof area (sf) x 1/12(ft) x 7.48 (gal/cubic foot) Basin area needed to store 1" rainfall supply from roof is (sqft) Assuming your basin is 8" deep | (1/12) ft of rainfall * (roof area) ft / (8/12) ft / 7.48 gal/cubic foot Your Annual roof rainfall supply is (gallons) Roof area (sf) x 1(ft) x 7.48 (gal/cubic foot) x 0.9 (runoff coefficient) Your Annual landscape rainfall supply is (gallons) Landscape area (sf) x 1(ft) x 7.48 (gal/cubic foot) x 0.4 (runoff coefficient) Your Annual greywater supply is (gallons) # of persons x 30 gallons per person per day x 365 days Your total local, renewable water supply is (gallons) Demand Your average annual water demand is (gallons/year) Average annual = average of January and July monthly water use inputs multiplied by 12 months Balance and Daily Total Your Water Balance* is (gallons/year) *If your water balance is positive – you have extra water to infiltrate into our aquifer. If it is negative, you use more water than you have the potential to capture in a year. Average daily use per person (gallons/day) Leave this field blank
