"I can't for the life of me see why you would not have a continued relationship for either stating the Government's position or stating the law as it applies to tribunals in the courts," Mr Key said.
"It's not a threatening conversation, it's just a statement of reality and I'm the Government's major spokesperson, I need to spell out the Government's position. The Government's long-held and very strongly held view is that nobody owns water."
On the concern that Mighty River Power share prices might be driven down by uncertainty over water ownership, Mr Key said: "If you have a change in ownership of a company that uses water, (the uncertainty) is not going to alter anything because at the end of the day the Government's view is that nobody owns water.
"And if that view was changed by the courts and upheld, then that would have a big impact on every business, irrelevant of what their ownership is."
Mr Key said the Waitangi Tribunal was "absolutely still relevant" and it was the "longstanding position of successive governments that from time to time they agree with those decisions but they don't always agree".
"There are some Maori that believe they own water ... (and) there are also Maori that believe they own the air and there's Maori that believe they own the geothermal assets. I would dispute those and the Government's view is that no one owns water. And that view is backed up by the Common Law position, not just in New Zealand but internationally."