"The good thing is that it will never happen," he said.

"There is no intention for it to happen."

The state government this week resisted a parliamentary order to release the project's long-delayed business case, which would reveal the cost of the scheme.

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On Thursday, Water Minister and Tamworth MP Kevin Anderson denied deliberately delaying release of information like the cost of the dam until after the May federal election.

He said keeping the dam's cost secret was necessary, so contractors could bid for the job.

"If you put the number out there, then there's no confidence in relation to them being able to put a number against what they're able to do," he said.

Mr Windsor, who represented Tamworth in state and then federal parliament from 1991 to 2013, said the dam was a dud project.

"That proposal's been around for years, I remember we looked at it 25 years ago and it was a dead dog then," he said.

The former MP said the project wouldn't provide even a year's supply of water for the city of Tamworth, and that the project would be so costly it would make Tamworth's water the most expensive in the country.

"My spies within the government tell me that it's not going to happen and neither should it," he said.

"But they're going to keep it alive until after the federal election. Then the Nationals - Joyce and co - will be able to conveniently blame the Labor Party for them not doing it."

Asked about Mr Windsor's comments, Mr Anderson said the former MP understood the cabinet-in-confidence process, in which cabinet documents are kept secret for 10 years.

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During a bruising estimates hearing with Mr Anderson on Wednesday, Labor MLC Kate Jackson suggested the state might be planning for Tamworth's water rates to double, but hiding the information in a document residents can't see, until after a decision was made to build the project by the state government. Mr Anderson refused to rule out a doubling of Tamworth water rates on Thursday.

The project's final cost, its cost-benefit ratio, where water will be allocated, the environmental costs, its owner and the anticipated impact on the cost of Tamworth's water supply are all currently unknown

The state government intends to keep the project's business case confidential, but will release the information in the project's environmental impact statement (EIS).

Mr Anderson said on Thursday the EIS would be put out to consultation "very soon". The business case is set to go to NSW cabinet at its next meeting.

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