rainwater collection (RWC) [%]

Percent (%) of annual water demand met by rainwater captured on site. The amount of surface area on site required to capture sufficient rainfall to meet the annual water demand for a project can be considered as the rainwater “footprint.”

To calculate the rainwater footprint, refer to annual climate information for areas near your site to get an estimate of the annual rainfall.

For example, Downtown Los Angeles averages 15.14 inches (384.6 mm) of precipitation annually. If you have a good estimate for the annual water demand for your project (e.g. X gallons / year), you can compare demand with available rainfall. It is important to note that rainfall in many climates is highly variable by season, so often large storage cisterns are necessary. Remember, always implement efficiency measures to reduce demand first.