Māori would argue that under the Treaty of Waitangi they already have ownership, because at no point was it given away or sold to the Crown. In order to charge for water the ownership issue must be resolved.
As part of the settlement, it is likely that Māori would receive a water allocation in under-allocated catchments. In over-allocated catchments it is likely Māori would receive a share of the revenue from operating the water market. In either case this outcome is more preferable than continuing to give away our fresh water resource to businesses (many of which are foreign-owned) to boost their profits.