About The Rainwater Harvesting Tank Sizing

The Rainwater Harvesting Tank Sizing tool estimates effective annual rainfall, potential annual harvest, average daily supply, dry-period tank volume, and annual demand coverage from roof area, rainfall, runoff coefficient, first flush, demand, and dry days.

How to Use the Rainwater Harvesting Tank Sizing Online

1. Enter roof catchment area and annual rainfall.
2. Set runoff coefficient and first-flush deduction.
3. Enter daily demand and the number of dry-period days to cover.
4. Calculate harvest potential, tank volume, and demand coverage.

Choosing Options Correctly

Use a runoff coefficient appropriate for roof material and collection losses. First-flush deduction should be smaller than annual rainfall and should reflect local water-quality practice.

Common Use Cases

• Estimate harvestable rainwater for a roof catchment.
• Size preliminary storage for a target dry period.
• Compare demand coverage under different rainfall or runoff assumptions.

Quick FAQ

What does this size?
It estimates storage from roof area, rainfall, runoff, and demand assumptions.

Does it guarantee water availability?
No. Actual yield depends on rainfall timing, first flush losses, roof condition, demand pattern, and dry periods.

Should I include overflow?
Yes. Every rainwater tank needs safe overflow and drainage for storms beyond storage capacity.

Can this be used for potable systems?
Only as a storage estimate. Potable systems need treatment, materials, testing, and local health requirements.