Hawke's Bay regional councillors have voted 5-4 to send a business case for the $600 million Ruataniwha water storage project to Deloitte for independent evaluation.
The business case contains information in the public domain, such as claims it will create 2500 jobs and produce revenues of $250 million per year.
The Hawke's Bay Regional Investment Company, which prepared the case, is advising the council to invest $80 million in the scheme. It says it could irrigate up to 30,000ha of land - providing farmers with security of water.
The four councillors who opposed sending the business case to the auditing firm said there was not enough detail in it to evaluate the risks and benefits.
Councillor Rick Barker questioned company chair Andy Pearce on why the business plan did not include any detailed spreadsheets with budgets.
Mr Pearce replied those detailed and commercially sensitive figures were being sent to the council's advisors Deloitte to consider on their behalf.
Mr Barker expressed surprise at the answer, saying he thought the council's investment company was its advisor.
Afterwards, Mr Pearce said he was happy with how the meeting went. "This of course is only another step in process and it now goes to Deloite to provide an independent assessment of the business proposition put before the council."
He said the future of the project rested on the regional council investing in it.
The Green Party says the business case assumes that at least one third of land in the Ruataniwha scheme will be used for dairying and that it will require a new milk processing plant.
However, Mr Pearce said the business plan made no assumptions on who the end users of the water from the scheme would be.