How to Calculate Rainwater Harvesting
What is Rainwater Harvesting?
Rainwater harvesting collects roof runoff for garden irrigation, toilet flushing, and laundry. UK average rainfall of 600-1,200mm annually can supply 30-50% of non-potable water needs.
Formula
Step-by-Step Guide
- 1Collection potential = Roof area (m2) x Annual rainfall (mm) x Efficiency factor (0.85)
- 2UK households use approx 150 litres/person/day; approx 50% is non-potable uses
- 3Simple water butts (200L) cost 30-60 GBP and pay back in one gardening season
Worked Examples
Frequently Asked Questions
What is Rainwater Harvest?
Rainwater harvesting collects roof runoff for garden irrigation, toilet flushing, and laundry. UK average rainfall of 600-1,200mm annually can supply 30-50% of non-potable water needs
How accurate is the Rainwater Harvest calculator?
The calculator uses the standard published formula for rainwater harvest. Results are accurate to the precision of the inputs you provide. For financial, medical, or legal decisions, always verify with a qualified professional.
What units does the Rainwater Harvest calculator use?
This calculator works with inches, litres, percentages. You can enter values in the units shown — the calculator handles all conversions internally.
What formula does the Rainwater Harvest calculator use?
The core formula is: Collection potential = Roof area (m2) x Annual rainfall (mm) x Efficiency factor (0.85). Each step in the calculation is shown so you can verify the result manually.
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