Water Tank Size Calculator
Add up the water you use each day and see how much tank you need to get through a dry spell.
This gives a tank storage estimate only. It assumes no rain falls during the dry spell you enter. Everything is worked out in your browser. Nothing is saved or sent anywhere.
1. House and garden
Your water bill or a meter on the tank outlet gives your real daily use. If you don't know it, start with the defaults and change them.
Everyone who lives there most of the time (0 to 50).
A common planning starting figure for in-house use. Your own use may be higher or lower.
Watering, washing down, a shed tap and so on. Leave at 0 if it's on a separate supply.
2. Stock and animals
Add each kind of animal that drinks from this tank. The example figures are rough only. Hot weather, dry feed and milking can raise water needs a lot, so check your state agriculture department's figures for your animals.
3. Dry spell and tank
How long the tank has to last with no rain coming in.
For example 60 days for a dry summer (1 to 730).
Extra for hot spells, visitors, leaks and the water left below the outlet (0 to 100%).
Used to show how many of that size you'd need. Check the maker's real capacity.
Results
How it was worked out
Before you rely on it
- This is a storage estimate only. It doesn't allow for rain topping up the tank during the dry spell, evaporation, or water that can't be drawn out below the outlet.
- For drinking water, keep the roof, gutters and tank clean, fit a first-flush diverter and get advice from your local council or state health department on treatment.
- Big tanks are heavy. A full 22,500 L tank holds about 22.5 tonnes of water, so it needs a level, properly prepared base. Follow the tank maker's instructions.
- To check whether your roof can actually fill the tank, use the Roof Rainwater Catch Calculator.