Verify the inputs
Measure or document each input. If a value is only an estimate, record its source and test a conservative alternative.
Wells & water/ CALCULATOR
Rainwater collection & overflow
Estimate one rainfall event and the amount a tank can receive.
FROM ESTIMATE TO ACTION
Use the result, not just the number.
Keep the calculation traceable
Save the input link or copied result together with the date, units and assumptions. A number without its inputs cannot be checked later.
Confirm the decision
Compare the estimate with the related guide, current product data and requirements that apply at your location before buying or building.
Inputs to verify
- Connected projected roof area (m²)
- Horizontal projected area that drains to the tank.
- Rainfall in the event (mm)
- Choose a rainfall event, not an annual average.
- Collection factor (%)
- Explicit assumption for losses before reaching storage.
- Tank usable capacity (L)
- Capacity excluding unusable dead storage.
- Water already in tank (L)
- Must not exceed usable capacity.