The Hamilton City Council has voted overwhelmingly in favour of restarting fluoridating its water supply.
The council have just voted nine to one in favour of its return.
It was expected Hamilton City Council would follow a referendum which showed residents want reinstatement, despite half of the councillors voting fluoride out of the water last year.
Today's vote was deferred until the council knew the outcome of legal action by the New Health group against South Taranaki District Council for adding fluoride to drinking water in Waverley and Patea.
New Health argued that adding fluoride breached people's right under the Bill of Rights Act to refuse medical treatment.
Earlier this month, High Court judge Rodney Hansen ruled South Taranaki had the legal power to fluoridate the water, but yesterday, New Health filed a notice of appeal in the Court of Appeal against the decision.
Now, Safe Water Alternative New Zealand (Swanz) has put Hamilton City Council on notice of a judicial review if it decides in favour of fluoridating tap water again.
The warning comes as the 13-strong council decides on the results of the non-binding referendum, in which 66 per cent of the 37,276 voters supported fluoridation.
Swanz co-ordinator Trevor Crosbie said the council was obligated under the Local Government Act to consult the public on the significant issue before making a decision.
"The point is that this is a brand-new decision and it cannot piggyback or rely on the previous special consultative requirements used for the old decision to cease fluoridation, at the time of the tribunal in June 2013."
That five-day tribunal attracted 1560 submissions - 1386 in opposition to fluoridation.
Following the tribunal, the then council voted 7-1 to stop adding fluoride to municipal water supplies.
Five councillors removed themselves from the vote, including Ewan Wilson, Martin Gallagher and former councillor Pippa Mahood, who declared a conflict of interest due to their roles as members of the Waikato District Health Board, which is mandated by the Ministry of Health to promote fluoridation.
But shortly after, Mr Gallagher called for a referendum on the issue.
The Herald understands the new council is likely to favour the referendum results, despite five of them - mayor Julie Hardaker, deputy mayor Gordon Chesterman, and councillors Angela O'Leary, Margaret Forsyth and Dave Macpherson - previously voting to get rid of fluoridation.
Though councillors had been warned not to air their views publicly, Mr Macpherson - who is away and can't vote - said he was personally anti-fluoride but would have voted in favour of reinstating it "because I respected the result of the referendum - because it was clear".
He believed other councillors would vote for reinstatement for the same reason.
Mr Wilson, who was criticised last year for not participating in the tribunal, said he had an open mind and there was no conflict this time because the DHB was not involved.
Hamilton began adding artificial fluoride to water supplies in 1966 to fight tooth decay and it's thought to save more than $1 million in dental care costs.
Anti-fluoride lobbyists claim it causes fluorosis (discoloured teeth), led to bone cancer, lowered the IQ of children, affected fertility and pregnancy and interfered with the thyroid.