Like the Ruataniwha scheme itself, the council's proposed water take from the scheme, and the cost of taking that water, the numbers are uncertain because nothing is confirmed.
On the water cost for example, while negotiations are ongoing, HBRIC has said the council cannot expect to pay less than other users, who will be charged 26 cents per cu m.
Based on the 2 million cu m the council has suggested it could take initially, that is a gross annual cost of $520,000 for Ruataniwha water.
But offsetting that is the increased rates the council could collect from new water users - domestic and commercial - who it is assumed will be attracted to the district by the dam.
There will be more clarity around the Ruataniwha numbers after March 31, the deadline HBRIC has given itself to finalise funding for the scheme and sign water take contracts for at least 40 million cu m a year - the minimum it needs to get the project off the ground.