More fluoridation of Hawke's Bay water will be strongly opposed by an anti-lobby group.
The Hawke's Bay District Health board would likely impose it on the whole region thanks to an upcoming law change.
Until recently Hastings' urban area was the only part of Hawke's Bay with fluoridation. It has been temporarily suspended while the water is being chlorinated but will resume shortly.
The rest of Hawke's Bay is permanently unfluoridated but that looks set to change.
A new law is expected to be passed in Parliament in about 18 months' time, allowing district health boards rather than local councils to decide on water fluoridation.
Councils would still be responsible for supplying drinking water and the cost of fluoridation borne by councils.
Mary Byrne, the national co-ordinator of lobby group Fluoride Free New Zealand, said the group was going to challenge the proposal after the legislation's first reading when it goes to a select committee.
"This is our opportunity to put submissions forward where we present information that fluoridation is not effective against tooth decay and rather has risks to dental health. We will show good alternatives for public dental health that work."
She said if the committee did not make the change they would have until 2018 before the law would be imposed.
Napier Mayor Bill Dalton said Napier would have no option but to comply with the new law.
"I very much value the purity of our water supply in Napier and my personal view is it should stay pure and untainted," he said.
"My view is while it has health benefits most thinking people will ingest enough fluoride by using fluoridated tooth paste."
"Those people that don't ensure their children's teeth are clean or don't clean their own teeth are probably not drinking water anyway - they are probably drinking soft drink."
Ms Byrne said that the biggest driver for tooth decay was poverty, not non-fluoridated water.
"The latest New Zealand study looked at school dental care, which included 45,000 kids in each age bracket. Of those the only difference was between Maori and non-Maori. Maori had the highest decay rates but that could be down to a whole host of things.
"For them just to say non-fluoride water is the problem when they do not know how much water [people are] drinking is ridiculous."
Hawke's Bay District Health Board (HBDHB) clinical director for oral health Robin Whyman said fluoridation was one of the most cost-effective public-health measures available.
Fluoridating Napier's water was previously ruled out because of the number of water-supply sources, but a Ministry of Health review of cost effectiveness indicated there would be benefits to Napier children and adults despite the technical difficulties and cost.
"Once the legislation had been through Parliament the district health board would again look at the merits of fluoridating all community drinking water supplies in the HBDHB region," Mr Whyman said.
"HBDHB strongly supports water fluoridation as the most cost effective way to reduce dental decay in children and adults who still have their own teeth."
Ms Byrne said programmes overseas such as the Scottish Smile Child programme were much more effective and less of a risk to dental health.
"They hold classes at childcare centres and junior schools that teach them how to look after their teeth. They found the amount of decay in children decreased by half."
The HBDHB's Maori Relationship Board is not unanimous in its support of fluoridation.
Maori Relationship Board member Lynlee Aitcheson-Johnson campaigned for a HBDHB seat in the recent elections on a fluoride-free platform.
"I would expect the Hawke's Bay District Health Board to enter into robust conversation with the community," she said.
"There are so many questions and recent findings with regards to the neuro-toxicity of fluoride."
She said fluoride was a recognised neuro-toxin sourced from a toxic waste product from the phosphate fertiliser industry.
"The HBDHB should investigate Scotland's Child Smile prevention dental scheme, achieved without fluoride and saving millions of dollars."
The New Zealand Advertising Standards Authority this month ruled in favour of Fluoride Free New Zealand controversial TV ads after several complaints of untrue claims of fluoride chemicals being toxic waste that "played on fear".
The authority ruled the ads were factual and did not unjustifiably play on fear.