All nine members of the Tamworth Regional Council (TRC) voted on Tuesday night to demand state Water Minister Kevin Anderson tell the community the true cost of the dam project.

Mr Anderson did not answer a series of questions about whether he would release additional information as a result of the council's call on Wednesday.

The government has previously refused to release the information in response to repeated demands, including by NSW Parliament.

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"The state and federal governments are committed to providing greater water security for Tamworth and the Peel Valley, which is why both Governments will contribute 100 per cent of the capital costs of building the new Dungowan Dam and along with stage 1 and 2 of the 55km pipeline," Mr Anderson said.

Motion sponsor and Labor councillor Stephen Mears said it was difficult to have confidence in the scheme, which will cost more than half-a-billion dollars, given the secrecy.

"There are already a number of concerned residents making representations to councillors and council," he said.

Deputy Mayor Mark Rodda said the people of Tamworth "deserve an explanation" as to whether the project stacks up. He said even council doesn't know the information, which has been kept confidential within government.

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He rejected the idea that the project budget had to be kept secret in order to not disadvantage bidders for the job.

"We saw that with the Chaffey Dam augmentation. The public knew how much it was going to cost, the estimated cost and the yield of the increase," he said.

"Obviously, the only thing we didn't know was how much we were going to be charged for the water. Ultimately, those three questions are probably pretty important with this proposal."

If the principles of full cost recovery were applied, Cr Rodda said the community would be left holding the bag for a bill of as much as $1.2 billion.

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He agreed that the decision to keep the information secret would undermine confidence in the scheme.

"I definitely think it would undermine confidence for the project in the people. I've received feedback from plenty of people that are quite dubious about the spend and the yield," he said.

Tamworth mayor Russell Webb backs the dam, but still voted to demand the extra information.

He said being kept in the dark "shouldn't undermine confidence in the project, but it probably will undermine confidence in the process:.

Tamworth council isn't the first representative body to ask for and not receive the information.

NSW Parliament passed a call for papers ordering Mr Anderson to release the project's entire business case, a document the state government plans to keep secret forever.

The cost of the project is due to be released in the project's environmental impact statement, which is due in the second half of 2022. The timing has left many concerned that the project could be signed off and funded before the public gets to know its cost.

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