I don't understand why charging for water intended for commercial export has to be an issue at all. This is a sovereign nation. We have a parliament with the power to make laws that affect this nation. Just pass a law slapping a charge on any water that is exported as water intended to be sold at a profit. How hard does that have to be? I don't see why it has to get all tangled up in issues of ownership, Maori rights and the like. Why complicate something that is simple?
Simply because it "is" as issue. The second you put a value on something that is free it becomes a trade-able commodity. Iwi will want their share because they are tangatwhenua, IRD will need processes in place to track and manage the tax take, and if it's too expensive companies won't produce here meaning loss of jobs. Start with bottled water where will it end? Not saying it's a bad thing, just we need some careful thinking considering the related consequences. If the bottled water take is so incredibly tiny (as is claimed) why would you create a system that would potentially cost more to manage and police than the tax you get?