Customers using an innovative leak-detecting device could save 10 million litres of water a day, according to a water company.
Thames Water said the LeakFrog devices can identify hidden leaks and alert homeowners to pipes that need to be repaired or replaced.
Undetected leaks can pile hundreds of pounds on to metered bills and potentially cause damage to properties and drive up home insurance costs.
During the last three years 70,000 homes' supply pipes across London and the Thames Valley have had LeakFrogs fitted.
Out of these, 2,100 homes were discovered to have large enough leaks to require repair or pipe replacement.
The LeakFrog gadgets are attached to a home's water meter overnight and work my measuring the speed that the water passes through.
Thames Water's Leo Kiernan, who co-created the device, said: "So far the LeakFrog has saved 10 million litres a day for our customers - that's four Olympic-sized swimming pools every single day.
"Reducing leakage is as important as ever right now as we face the prospect of a very dry summer.
"Although reservoirs in London and the Thames Valley are more than 90% full, we don't know what the weather will bring."
© Press Association 2011