Farmers must now decide if they will sign up to the scheme, otherwise it may fold.
For farmers with existing resource consents to draw water, scheme water is a "bird in the hand" scenario because consents could be limited in future years.
Critics of the scheme have said the scheme will result in more dairy farms, but Federated Farmers Hawke's Bay president Will Foley said at 23c the region would remain largely sheep, beef and cropping.
"Current dairy farmers, especially ones that are irrigating, seem to think that it is too much on the high side for them. Irrigating grass needs a lot more water than irrigating crops - grass is not an efficient user of water. Crops are."
Mr Hansen said the scheme would reliably distribute 104 million cubic metres of water per year, from the initial 90 million cubic metres per year planned.
"Using its extensive expertise in dam construction, OHL-Hawkins has been able to create a significantly more comprehensive scheme, which offers additional value while still remaining within the range of the feasibility report cost estimates," he said.
Construction contract discussions will continue into June. OHL-Hawkins Joint Venture bid manager Steve Livesay said lessons learned in Canterbury and Australian schemes contributed to the scheme design.
The Board of Inquiry - set up by the Environmental Protection Authority to hear evidence and submissions on Tukituki Plan Change 6 and the scheme's resource consents - will deliver its draft decision no later than April 15, before releasing a final decision by May 28.
The Hawke's Bay Regional Council-supported scheme has the potential to supply 25,000-30,000 ha and ensure minimum river flows. The council said the scheme was expected to create about 2250 new jobs.