But Mr Key said, that in his view, "no one owns water".
"It's like air. No one owns air."
He was confident the Maori Party would remain a support partner for National for the next three years.
Mr English said through both the Iwi Leaders Group and the Land and Water Forum there had been a lot of discussion with Maori in the past few years on water.
"There has been a general agreement that there is no mechanism to determine the ownership of water. It's a public good, like the air.
What matters is how it is used and the rules that apply to that use."
Sir Tumu te Heuheu is leading a national hui on freshwater at Hopuhopu on February 23 and 24.
Mr English said that while there had been settlements with iwi on co-management of lakes and rivers, no settlement had ever provided for the ownership of water - and it would not in the future.
"It is not up for negotiation."
Maori Party MP Te Ururoa Flavell has encouraged iwi to take High Court action in a bid to stop the sales.
Nick Davidson, a retired lawyer and Treaty settlements expert, said he did not believe court action or tribunal action would succeed. He believed it was a power-play to get preferential ownership shares of the SOEs.