When it rains each square metre of roof collects 1 litre of rainwater for every 1mm of rainfall.
The potential volume of water available for harvest is dependent on

• your local rainfall
• the area of suitable roof available for harvesting

You will only be able to harvest the rainwater from those parts of the roof where the downpipes from the gutters can be directed to a tank.

How much rainwater falls on my roof each year?

To calculate the maximum volume of rainwater you could harvest from your roof, enter that area and your annual rainfall in the space below.

Rainfall data is available from www.bom.gov.au.

Theoretically, you could harvest