The regional council has committed ratepayers "in principle" to a $43.1 million buy-in to the Ruataniwha dam, $8 million more than was originally reported.
Councillor Tom Belford said the number $35 million got put on the table because "there was a little back-of-the-envelope calculating going on" when council staff could not provide a total cost of the commitment when questioned about it at last week's meeting.
"But, in fact, in the letter that Andrew Newman sent to the council which was a part of the agenda papers they estimated the cost of this to be $43.1 million," he said.
"It is impossible to understand how you could argue that that was not something requiring public consultation."
According to the letter referred to by Mr Belford, the proposal on offer would see the regional council enter into a 35-year water user contract, based on the foundation water user agreement.
"HBRC will receive 30Mm3 [30 million cubic metres] in total of water at zero cost up until year 10," he wrote.
"From year 10 onwards HBRC will purchase 4Mm3 per annum of water on the same terms as foundation water users except the cost will be calculated only on the volumetric charge and excludes the variable energy charge."
He then provides the cost to the regional council under a summary of the new proposal.
"[The] 35-year cost of the water to HBRC [equals] $43.1 million, calculated as Annual Volumes nominal HBRC Water Price Payable," he said.
It is this revelation that has prompted councillor Peter Beaven to seek advice from council staff on how to address the issue of a lack of public consultation before such as decision was made by council, even if it was in principle.
"I am really concerned about the nature of the commitment we have made here," he said.
"If we haven't gone through due process in terms of public consultation then what are our options here?
"Can we extricate from it is the question I am asking. Can we extricate ourselves from the apparent obligation or commitment that we made and follow due process? And I have no idea what the answer to that question is, that is why I have raised it."
He said he has asked the council what the options are going forward.
"Given that we theoretically made a commitment, granted the commitment we made was subject to a few things, but it wasn't subject to public consultation so how do we insert that into the deal," he said.
Regional council chairman Fenton Wilson said the council had sought advice on the issue from Audit New Zealand.
He also said the fact the Office of the Auditor-General was involved might be quite useful as well.