Rainwater harvesting in England's back gardens is the latest idea to save money and cut demand for water.
Campaigners say rain harvesting could prevent flooding
The new Rainwater Harvesting Association wants people to bury a submarine-shaped tank in their gardens to catch rain off roofs.
The saved water could be used to flush toilets as well as prevent flooding by containing excess rainwater.
This could be useful as climate change is likely to create drier summers as well as more flooding.
The association is being promoted by the Environment Agency, which says rainwater harvesting is particularly good for offices, factories and public buildings.
The association said "less than 1% of the water treated by public water systems is actually used for drinking and cooking".
Every time a toilet is flushed, between 7.5 and 9.5 litres of drinking water goes down the drain, the association said.
Other wasteful examples include up to 540 litres used by a garden sprinkler an hour, and 65 litres used in a typical washing machine cycle, it said.
The association said people would get their money back from the tank investment within as little as five years, plus there are government grants available for help with capital costs.
The initiative comes in the week that Thames Water is considering an expensive, energy-hungry desalination plant to solve the shortage of water in the south-east of England.