The New Zealand Dental Association is "greatly alarmed" by fluoridation being stopped in Wellington and says the Government must intervene if a solution isn't promptly sorted out.
Wellington has been supplied with low and inconsistent levels of fluoridation in its water supply for four years, a review has found.
As of last month, Upper Hutt, Porirua and Wellington City haven't been receiving fluoridated water at all. The amount of work needed to fix the problem means this could carry on for the rest of the year.
New Zealand Dental Association spokesman Dr Rob Beaglehole said he was "greatly alarmed" by the decision to switch off community water fluoridation in parts of Wellington.
"This will impact on the communities of Upper Hutt, Porirua and Wellington, which are communities that are already impacted by oral health inequalities."
Beaglehole said an immediate solution must be found.
"We call on the Government to act, if a regional solution isn't promptly implemented."
Wellington Water operates water treatment plants on behalf of Greater Wellington Regional Council and delivers the bulk drinking water supply to Lower Hutt, Upper Hutt, Porirua and Wellington cities.
Regional council chief executive Nigel Corry said the fluoridation machinery was more than 30 years old and no longer met acceptable performance standards, "the outcome of which is a low and inconsistent level of fluoridation in our water but it's also an opportunity to invest in an upgraded system."
The fluoride dosing facilities at the water treatment plants have been operating inconsistently for about four years, so operators have been conservative with fluoride dosage.
A review of the situation was only commissioned when the issues with the facilities become "too onerous".
The review, which was received last month, also identified operational health and safety risks at the Te Marua and Gear Island Water Treatment plants.
Upon receiving the review, Wellington Water decided to turn off the fluoride facilities at these two plants while work is undertaken to reinstate the service.
This means Upper Hutt, Porirua, Wellington City, Stokes Valley and Manor Park have not been receiving fluoridated water since last month.
Wellington Water regulatory services director Charles Barker said it's expected work to repair equipment at the Te Marua Water Treatment Plant will take up to nine months.
"We are working on ways to return fluoride to the water supply at our Te Marua and Gear Island Water Treatment Plants.
"We are also working on ensuring that we are able to consistently fluoridate the drinking water at all our water treatment plants in a way that provides the expected health benefit."
Wellington Water is still evaluating what work is required at Gear Island Water Treatment Plant.
The review has made several recommendations, which Wellington Water will work to implement as a priority with funding from Greater Wellington Regional Council.
"It is important that we supply safe and healthy drinking water to our communities," Barker said.
Wellington Water's other fluoride facilities, based at the Waterloo and Wainuiomata water treatment plants, remain operating.