formula: Roof Area (ft2) X Precipitation Amount (in) X 0.623 = Amount Collected (gallons)
example 1: if the portion of your roof is 120 square feet, an inch of rainfall will send 75 gallons to the cistern. (120 ft2 X 1.0 in X 0.623 = 74.76 gallons)
example 2: if the portion of your roof is 400 square feet, 1.5-inches of rainfall will send 374 gallons to the cistern. (400 ft2 X 1.5 in X 0.623 = 373.8 gallons)
A cistern collects + stores rainwater, usually from a roof, for use later in the garden. When the cistern is full, overflow rainwater can be directed to a dry creek or landscape drain.
Projects that feature a cistern: