Fluoride is helpful in preventing tooth decay, but some say the government shouldn't be in the compulsory medication business.

An anti-fluoride group has crowdfunded almost $30,000 to fund a controversial national ad campaign with claims scientists call misleading.

Fluoride-Free NZ bought four primetime ad spots on July 31 for thousands of dollars each, and plan to keep the campaign going. These are their first national TV ads.

One ad compares New Zealand's fluoridation with other countries while the other describes fluoride as a "toxic chemical handled by workers using hazmat suits".

Fluoride is a chemical added to more than half of New Zealand's drinking water in minuscule amounts to promote healthy teeth.

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While fluoride can be toxic in large amounts, the Ministry of Health said a person would need to drink thousands of glasses of water in a single sitting to obtain anything near a lethal dose.

A 2009 study found that Kiwi children in areas with fluoridated drinking water had 40 per cent less tooth decay than children living in areas without, on average, and the government health officials around the world are fans of the practice. However some people find the practice abominable, arguing that Kiwis should have the right to choose what medicines they take.

The ads aired twice during TV3's Newshub, during a showing of Mrs Doubtfire, and during Prime News.

The campaign is part of a wider push that included a televised debate on the FACE channel. The group is raising funds through the Spark Foundation's Givealittle website.

"The goal of the campaign is to make people aware of fluoridation," Fluoride-Free spokesman Don Church said.

"Particularly the waste ad - most people aren't aware where this chemical is coming from, or what it is that is going into community water supplies. It's not pharmaceutical grade chemicals at all."

"The other ad brings people's awareness to the fact that the number of countries that fluoridate are in the minority. In Europe many countries have rejected flouridation."

The USA and UK are among the other countries that fluoridate their water.

Ministry of Health's Stewart Jessamine said the chemicals used in water treatment were purchased from supply companies and complied with rigorous standards for purity and quality. Those standards can be viewed here.

"The Ministry of Health strongly supports water fluoridation as a safe, effective and affordable way to prevent and reduce tooth decay across the whole population," Jessamine said.

Daniel Ryan of pro-fluoride group Making Sense of Fluoride said the ads were misleading.

"The simplicity of Fluoride-Free NZ's message ignores the inevitable complexities that accompany many scientific topics," Ryan said.

Comparisons between New Zealand and other country's water fluoridation ignored naturally occurring fluoride in water, as well as artificially fluoridated milk and salt.

"There is much scaremongering and misinformation around fluoridation on the internet and in alternative media. It is easy for the public to become confused about the evidence, and start to believe that fluoride is harmful," Ryan said.

One expert approached by Stuff said he had promised his wife to stop commenting on fluoride stories after receiving violent threats when he spoke out in the past.

EXPECTING COMPLAINTS

Advertising Standards Authority (ASA) boss Hilary Souter said she expected complaints about the ads.

"It's a topic that generates complaints as a rule."

The industry standards body has fully upheld six of eight complaints against the group in the past three years. One of the complaints was partly upheld, while one was rejected.

"The ASA doesn't take a position on whether their science is better than your science," Souter said, but ads are required to not actively mislead the public.

"We also have an advocacy rule. If you are taking a particular position on something then you get a long piece of rope."

Fluoridation complaints are so common that they are used as an example in the ASA's code.

Ryan's group planned to take a complaint to the ASA, and questioned TV3-owner Mediaworks' wisdom in airing the ads at all.

"Given Fluoride-Free NZ's history of false advertising and their unscientific stance on water fluoridation, I would hope that Mediaworks submitted these adverts to a high level of scrutiny before deciding to broadcast them," Ryan said.

"It seems surprising that Mediaworks would not find anything of issue in the adverts."

Mediaworks said the ads had been approved by the Commercial Approvals Bureau before airing. The group uses the ASA code.

Church of Fluoride-Free NZ said he expected any complaints to fail.

"You look at those ads and ask yourself 'what in those ads is untruthful?'"

DHBS TAKING CONTROL

The wider ad campaign is in part a response to a recent proposal to hand over water fluoridation to District Health Boards (DHBS), taking away control from local councils.

Health Minister Jonathan Coleman announced the upcoming legislative change in April.

The Ministry said 1.45 million Kiwis live in places without fluoridated water and subsequently miss out on the health benefits.

Anti-fluoride groups have been embroiled in legal and political battles up and down the country over fluoridation.

Christchurch water remains unfluoridated, while Auckland, Wellington and Dunedin all add it to their water.

Two non-fluoridated taps are now available in Hamilton, after fluoride was temporarily removed then reintroduced to the city's water supplies earlier this decade.

The change has widespread support in Parliament, with Labour's shadow Health Minister Annette King saying fluoridation was "never an issue for local government".

Fluoride-Free NZ and other anti-fluoride groups strongly oppose the proposal.

​"People like freedom of choice. They don't like being dictated to by compulsory medication," Church said.