Rainwater Harvesting Tank Sizer

Enter your roof size, pick your nearest city to load historical rainfall data, tick the water uses you want to cover, and get a recommended tank size, first-flush diverter volume, and estimated annual savings on your water bill. Runs entirely in your browser - nothing uploaded.

Tank size in L + gal Runoff coefficient ? First-flush diverter ? Monthly supply vs demand chart 20-city rainfall database Annual savings + payback

Units

Roof

Catchment area

m²

Roof type

Runoff coefficient ? 0.85

Rainfall

City (average annual rainfall)

Or enter custom annual rainfall (mm/yr)

Non-potable water demand

Toilet flushing (~50 L/person/day)

Household size (people)

Garden irrigation (custom L/day)

Laundry (~50 L/wash)

Washes per week

Savings & Payback

Water rate (per m3) ?

Total system cost (installation)

Recommended tank size

Annual yield ?

Annual demand

First-flush diverter ?

litres

Estimated savings

Payback

System cost payback -

Tip: a first-flush diverter is inexpensive (<£20) and significantly improves water quality. Size it to the volume shown above.

Monthly supply vs demand