Rainwater Firm-Yield Calculator

How much water can your roof reliably supply?

RAINFAL runs a daily water-balance across decades of local rainfall to show whether a system would have met demand every day — even through the worst drought on record. Research led by Dr. Robert Mace and Ricardo Briones at The Meadows Center for Water and the Environment.

84+
Years of rain data
20
Texas stations
Daily
Water balance
Start designing
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System design

Roof or other surface that catches rain, in square feet.
How much water your tank can hold, in gallons.
Water used per day. A water-efficient home uses about 25 gallons per person.
Share of rain that reaches the tank.
Adjusts the local rainfall up or down. 1.00 = records as-is; 1.10 = 10% wetter, 0.90 = 10% drier.
How full the tank is when the simulation begins, as a percent.
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Reliability
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Avg days dry / year
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Lowest storage
Tank storage over the record
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