Deloitte has also been supplied with a significant amount of financial modelling and data from HBRIC which is not included in the business case because it is considered commercially sensitive.
"A number of the matters on which councillors wish to delve into fine detail are not appropriate, in my opinion, to be dealt with in a public forum," HBRIC chairman Andy Pearce told the meeting.
Four of the council's nine councillors - Tom Belford, Rex Graham, Peter Beaven and Rick Barker - unsuccessfully attempted to pass a motion requiring more detail be included in the business case.
"Much more robust financial modelling needs to be made available before any decision to proceed could be made," the four said in a statement released after the meeting.
"We agree that water storage is a long term need for continued economic development of Hawke's Bay but the business case presented to the Regional Council is not yet a compelling case for the investment of $80 million of ratepayer funds."
Dr Pearce said HBRIC was following a process requested by the council resulting in a significant amount of information being provided to the council's advisers who would then report back.
Regional Council chairman Fenton Wilson said he agreed councillors needed more detail before making a decision on the investment.
"We do need to see more but today is not the day. There is a process we are entering into and it's fairly clear cut that a lot more work has to be done before this council can be satisfied that an independent party has verified, or otherwise, the business case from HBRIC."
The Deloitte report will consider the financial feasibility of the Ruataniwha scheme.
The council has commissioned a separate report from consultants Nimmo-Bell & Company who have been asked to identify and evaluate alternative investments HBRIC could make, rather than investing in Ruataniwha. That report is also due to be considered next month.
