water-harvesting

Rain Barrel Calculator: How Many Barrels Do You Need for Rainwater Harvesting?

Rain Barrel Calculator: How Many Barrels Do You Need for Rainwater Harvesting? A 1,000-square-foot roof section sheds approximately 623 gallons of water per 1 inch of rainfall, calculated as roof area (sq ft) x rainfall (inches) x 0.623. A single 50-gallon rain barrel captures only 8% of that water. Most homeowners need 2-4 barrels connected in series, with overflow directed to a rain garden or dry well. I installed a 3-barrel system (165 gallons total) under a 900-square-foot roof section at my Zone 6b property two years ago. The total cost was $185 for three recycled food-grade barrels, $42 in fittings, and $28 for a first-flush diverter -- $255 total versus $420 for comparable prefabricated units. Over 22 rain events last season, I captured roughly 2,800 gallons that would have otherwise eroded the foundation bed. At my local water rate of $0.008 per gallon, that is $22.40 in saved water...