The CAN Rating System 

Tankworld has developed a ‘CAN’ Rating System to illustrate how effective a rainwater tank might be in supplying 20% of average domestic needs over a 2 month period. Obviously, that’s conservative.

The rating is a scale from 1 upwards, where a rating of 1 represents a 1 week supply of water at 150 litres per day, and a rating of 10 represents a 2 month supply at the same rate.

The system is calculated using a domestic roof catchment area of 100 square metres, with collection from 2 downpipes.

Rainfall figures and other statistics used in these calculations are averages obtained from various water authorities, including City West Water, South East Water Authority and Yarra Valley Water Authority.

Basic calculation data:

• 1mm of rain falling on a catchment area of 1 square metre will provide 1 litre of water.
• The average home will use 260,000 litres per year.
• 1 toilet flush uses around 4.5 litres of water.
• An average load of washing uses 150 litres.
• A lawn sprinkler uses around 15 litres per minute.

Use the calculator to get a feel for the size of tank your home needs. If you find it complicated, just call us and we will guide you through the process.