How does the Rainwater Harvest Calculator work?

Calculate: Annual collection = Catchment area × Annual rainfall × Collection efficiency Then: Roof collection: 90% efficiency, pavement: 70%, storage needed for dry periods Then: 1000 m² roof, 1 m rain: 700-900 m³ water available.

Can you give an example of how to use the Rainwater Harvest Calculator?

Example: Input Residential roof 100 m², annual rainfall 500 mm gives a result of Annual collection ~45 m³ (45,000 L), covers 30-40% irrigation needs (Location dependent).

Is the Rainwater Harvest Calculator free to use?

Yes — completely free with no registration, download, or subscription required. All calculations happen instantly in your browser.

How accurate is the Rainwater Harvest Calculator?

Our Rainwater Harvest Calculator uses verified mathematical formulas and is accurate to multiple decimal places. Results are calculated in real-time using the same methods used by professionals.

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Rainwater Harvest Calculator

Rainwater Harvesting Calculator

Roof Area (m²)

Annual Rainfall (mm)

Efficiency

Rainwater harvesting collects precipitation for irrigation, toilet flushing, or emergency use. It reduces groundwater demand and stormwater runoff.

Difficulty:intermediate

References

›Rainwater Harvesting — Wikipedia

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Rainwater Harvest Calculator

Rainwater Harvesting Calculator

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Rainwater Harvesting Calculator