How much water can I collect from my roof?

TexasReviewed October 2026

A rule of thumb from the Texas Water Development Board is about 0.62 gallons per square foot of roof per inch of rain, before losses. Real systems typically capture about 75 to 90 percent of that. For example, the TWDB estimates a 2,000-square-foot roof collects roughly 34,000 gallons a year in Austin but only about 9,000 gallons in El Paso, because rainfall differs so much across Texas. Size your storage tank to cover the longest dry spell you expect, since rain does not arrive evenly. Use your roof's footprint, not its sloped surface area, and your local average rainfall to estimate.

Check your local rule. This varies by state, county or city. Your permitting office has the final word; the official lookup pages below show you who that is.

Sources

Find the rule for your area

Official pages from the agencies and code bodies that set these rules.

Want help planning your site?

We can walk you through what your land needs before your home ships.

Call 800-259-1745

General information, written in our own words from the sources listed with each answer. It is not legal, engineering, tax or financial advice. Rules change and differ by state, county and city, so confirm with the office that issues your permit before you build. Last reviewed October 2026.