Inputs
Enter roof or catchment area.
We normalize for calculation.
Use monthly or annual rainfall depending on the period selected below.
Rainfall depth over the selected period.
Choose whether rainfall represents one month or one year.
Surface type affects runoff efficiency.
Accounts for runoff loss, first flush, filters, splash, and imperfect capture.
Enter available storage to compare capture vs storage.
Storage capacity is used to estimate overflow.
Optional planning number for irrigation, household, or project use.
Used to estimate how many days collected water could last.
Planning-level tool.
Actual collected water depends on roof slope, rainfall timing, gutter design, losses, maintenance, first-flush diversion, and storage availability.
Results
Potential capture vs available storage.
—
Estimated water captured
—
Potentially stored
—
Estimated days of supply
Scenario comparison
| Scenario | Captured | Stored | difference |
|---|---|---|---|
| Ideal (100% efficiency) | — | — | — |
| Your selection (—) | — | — | — |
—
How we estimate
- Potential capture is based on catchment area × rainfall depth × a unit conversion factor.
- 1 inch of rain on 1 square foot yields about 0.623 gallons before losses.
- Efficiency adjusts for runoff losses, debris, first flush, and imperfect collection.
- Stored water is limited by available tank capacity.
- Days of supply = stored water ÷ average daily use.