New study shows rainwater harvesting can provide reliable water supply anywhere in Texas, even in drought

A groundbreaking study from The Meadows Center for Water and the Environment at Texas State University provides Texans with new evidence that rainwater harvesting is not just an add-on, but a practical and fully reliable water-supply option anywhere in the state, even during the most severe droughts.

Authored by Robert E. Mace, Ph.D., executive director of The Meadows Center, and Ricardo O. Briones, a TXST sustainability program graduate, the report, “Reliable Rainwater Is Only a Roof Away: The Firm Yield of Rainwater Harvesting in Texas,” introduces the Rainwater Assessment and Interactive eNumator for Firm-yield Analysis Limits (RAINFAL) tool that quantifies the reliability of household-scale rainwater harvesting systems across the state.

“Our analysis shows that rainwater harvesting is a legitimate, quantifiable water-supply strategy,” Mace said. “With the right design, these systems can reliably meet water needs anywhere in Texas.”

Using RAINFAL, the team evaluated the performance of different roof sizes, storage capacities, and household daily water use at sites across all regional water planning areas in the state to calculate the amount of water a system can provide as a 100% reliable supply under drought-of-record conditions.

 The results show that a 3,000-square-foot roof with 30,000 gallons of storage can meet indoor household water needs statewide, even under drought-of-record conditions. Larger catchments, more storage or reduced water use can further increase yields. 

“These results clearly show that rainwater harvesting belongs in the state’s water planning toolbox,” Mace said. 

Furthermore, system reliability for rainwater harvesting hinges primarily on design choices (such as the collection area and storage size) and user demand, rather than historic droughts defined by nearby reservoirs or aquifers. This new understanding means that each water supply, including each rainwater harvesting system, experiences drought differently and that planners should not assume that one drought-of-record applies to all water supplies.

Notably, the authors also concluded that widespread rainwater harvesting would not meaningfully reduce water levels in rivers and aquifers. The impact is negligible—less than a 1% reduction in runoff and recharge—especially given the greater changes to water flow caused by existing urban development.

The report, RAINFAL tool and user guide are available at meadowscenter.txst.edu/research/water-conservation/rainwater-firm-yield. By offering a simple way to calculate firm yield, RAINFAL enables Texans to make informed decisions about using rainwater harvesting in their communities and in long-term water planning.

“We made the RAINFAL tool free and accessible to help take the guesswork out of rainwater harvesting,” Mace said. “Now, anyone can model and evaluate a system that fits their water needs to see what’s possible.”

The study was funded by a student research endowment established by the Meadows Foundation and the National Oceanic and Atmospheric Administration.