Rainwater Harvesting Calculator

For every 1 inch of rainfall on 1,000 sq ft of roof, you can collect approximately 623 gallons of water (minus losses from evaporation and inefficiency). A 1,500 sq ft roof in an area with 40 inches of rain could collect over 33,000 gallons annually.

Rainwater harvesting is legal in most US states, but regulations vary. Some states actively encourage it with tax credits, while a few require permits for large systems. Check your local regulations before installing.