Water & environment
Rainwater harvesting potential Calculator
Estimate annual collection and a chosen dry-period storage buffer. This free rainwater harvesting potential calculator shows the calculation and its assumptions so you can compare your own figures.
Your results
Estimate annual collection and a chosen dry-period storage buffer.
Calculated outcomes
- Annual Demand Litres
- 54,750 L
- Annual Volume Coverage Percent
- 100%
- Desired Buffer Litres
- 3,150 L
Assumptions and estimates
- Method: Collection litres = roof area × rainfall × runoff fraction × filter fraction. Buffer = daily demand × chosen dry days.
- Annual yield is an upper-level estimate, not a time-series storage simulation. Seasonal mismatch and overflow reduce usable yield. No drinking-water suitability is assessed.
Useful next steps
- Use Compare options to test an alternative side by side.
- Copy, print or download a record of this calculation when you need one.
Reports open your email app addressed to s@s1.ie with the public page address only. Your inputs are never added.
How the rainwater harvesting potential calculation works
Collection litres = roof area × rainfall × runoff fraction × filter fraction. Buffer = daily demand × chosen dry days.
Annual yield is an upper-level estimate, not a time-series storage simulation. Seasonal mismatch and overflow reduce usable yield. No drinking-water suitability is assessed.
Using this calculator
- Enter your own figures in the labelled inputs. Keep the currencies, units and time periods consistent.
- Choose any applicable rate profile, pattern or assumption shown for this tool. Open additional inputs when relevant.
- Review annual collected litres and tank days of demand, then read the stated assumptions and eligibility conditions before using the result.
Worked example
This is a static example using illustrative inputs, not facts about you or today’s date. The displayed eligibility selections and assumptions apply only to this example.
See example inputs
- Roof catchment area (m²)
- 120
- Annual rainfall (mm)
- 1000
- Roof runoff efficiency (%)
- 85
- Collection/filter efficiency (%)
- 90
- Daily non-potable demand (litres)
- 150
- Tank usable volume (litres)
- 3000
- Chosen dry-period buffer (days)
- 21
- Annual Collected Litres
- 91,800 L
- Tank Days Of Demand
- 20