How long would the water last in a drought?
Check the tank size calculator. You can calculate from the size of your roof and average rainfall figures in your area (available on our web site) how much water will come off you roof in a year. The same calculator works out how long the water will last in a drought from a) your garden size, b) how much water you want to give to your plants, and c) the size of your tank. Aim for between 1 and 4 weeks drought protection and a tank size which also suits your budget.
