"We've yet to hear how financial scale benefits are derived from networking assets across regions, or on either side of the Cook Strait," he said.
"The new model will also create a convoluted, multi-layered governance structure that will erode public accountability, the fear expressed by several mayors, including Auckland Mayor Phil Goff.
"It must be for councils to decide how they do right by their communities," he added.
"National agrees there are complex problems, and we support a stronger water regulator with more power to set and importantly enforce standards, but we believe we should be incentivising change where it is led locally and able to happen organically, not dictated by the Minister.
"National will continue to protect local accountability and strongly oppose the Labour government's centralisation and control agenda."
Carter said Luxon was right.
"We've had some information (from the Minister), but not enough to prove that the Far North would benefit from the reforms," he said.
"There are bigger issues than Three Waters though. What seems to be happening is a process of centralisation, with water, Significant Natural Areas, building, all sorts of areas. My fear is that they are taking the local out of local government, and communities are losing their voice. And we've heard about economies of scale, which haven't been realised, in the past.
"Luxon's right, we should be concerned about what's happening and what the end result is likely to be."