A DARLING Downs resident has invented a valve that stops the average household losing 16,000 litres of water down the drain.

Lloyd Linson-Smith's Enviro Save device diverts and saves cold water that flows from domestic taps before hot water arrives.

It has won a segment on the ABC's New Inventors television program, has been described as the breakthrough of century, and is now in commercial production.

The $198 valve can be fitted to plumbing systems in new homes or retro fitted to older style houses for $475.

Mr Linson-Smith, 77, got the idea after he moved from Brisbane to Oakey, where his new home was supplied by tanks.

"We used to save the cold water in buckets for use in the garden but then my wife said, 'Okay smart arse, you have spent a lifetime as a tool and light machinery manufacturer so you should be able find an easier way to save our precious water'," he said.

"So I came up with the idea of a brass valve that is installed in the hot water pipeline just before the kitchen sink," he said.

"The cold water ahead of the arrival of the hot water is identified by a thermal element and bypasses the sink.

"The tap handle is the trigger for a process where potable cold water is returned to tanks."

Retro fitting was more expensive because it also required a tank and a pressure-reducing valve to save the cold water, which was fed back into the distribution system.

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But Mr Linson-Smith said: "When a three-person house can save 40 litres a day or 16,000 litres a year it does not take long to get the investment back.

Support for the valve is increasing, with the Toowoomba City Council announcing a $200 rebate for everyone who installs Mr Linson-Smith's system.