Understanding Rainwater Harvesting
The basic formula is: Gallons = Roof Area (sq ft) x Rainfall (inches) x 0.623 x Collection Efficiency. One inch of rain on one square foot yields 0.623 gallons. Efficiency depends on roof material, gutter losses, and first-flush diversion. Metal roofs provide the highest runoff coefficient (95%), while green roofs absorb more water (50%). Collected rainwater is ideal for irrigation, toilet flushing, and laundry.