THERE wasn't any champagne on offer at the NSW coalition's WasteWatch prize - just an expensive glass of water.

Retired water treatment engineer Ken Quick won $1000 for his entry which claimed Sydney's $1.9 billion desalination plant is money down the drain.

His research topped 46 other entries in the competition organised by the NSW opposition, which set up WasteWatch to monitor alleged poor state government spending decisions.

The controversial desalination plant at Kurnell was switched on in January, pumping purified sea water into the city's drinking supply.

At capacity, it generates 250 million litres of water a day, providing about 15 per cent of Sydney's water supply.

But Mr Quick sank the boot into the project after spending about 72 hours studying the plant and its costs.

"Our dams are now at 60 per cent capacity. When this contract was originally mooted four or five years ago we were at a 35 per cent capacity," Mr Quick told reporters.

"The government at the time were going to sign a contract if the dam levels went down to 30 per cent but it never ever did.

"However, they went ahead with this plant."

He claims the plant is currently only suppling 0.15 per cent of Sydney's drinking water.

"That's very inefficient," Mr Quick said.

Liberal backbencher and WasteWatch chairman Jonathan O'Dea took a sip of water from a glass full of gold coins at the prize ceremony today at NSW Parliament House.

"This is the most expensive glass of water I've ever tasted," he said.

"If you would have spent almost $2 billion on stormwater harvesting and recycling water you would have got a lot more for your money."

Mr O'Dea said the prize's 47 entries uncovered an alleged total of $17 billion of wasted taxpayers' dollars in the current government's three years in office.

"Waste is endemic in this state Labor government," he said.

"That $17 billion is equivalent to one third of the annual NSW budget."

Mr O'Dea said other entries identifying waste included buses used for the APEC summit in Sydney two years ago rusting in a police yard, and transport blowouts.

The opposition says it will launch a WasteWatch website next week to monitor wasted taxpayer dollars.