Ngai Tahu and the country's third biggest tribe, Ngati Kahungunu, have agreed formally on what the Hawke's Bay Regional Council needs to do before the South Island iwi backs the Ruataniwha Dam.
In September, Ngai Tahu publically indicated its interest to invest in the Ruataniwha Water Storage project.
And Ngati Kahungunu says it was given an assurance by the South Island tribe it wouldn't proceed with a bid if Ngati Kahungunu wasn't happy.
Ngati Kahungunu iwi chair, Ngahiwi Tomoana, says the agreement outlines requirements covering areas such as the environment, the economy and culture.
The chief executive of Ngai Tahu's commercial arm, Mike Sang says, it wants to be confident its potential new investment aligns with the values of all the parties.
