The South Taranaki District Council has a duty to fluoridate its water supply, as residents in the area have poor oral hygiene and a high level of tooth decay, the Supreme Court has been told.
A group opposed to fluoridation, New Health New Zealand, has taken legal action against the Council which has now reached the country's highest Court.
Earlier the Court of Appeal and High Court threw out legal challenges by the group, rejecting its suggestion that fluoridation of the water breached the right to refuse medical treatment.
However South Taranaki District Council's lawyer, Duncan Laing, told the Supreme Court today that health legislation places a duty on local authorities to improve and promote health in their areas.
He said a doctor had suggested that fluoridating the water supply was a much better way of improving oral health in the area, than other possible methods targeting dental hygiene.
"In Patea it was a doctor's opinion that if the toothbrush and toothpaste were free there was no reason to believe they would be used."
He said the doctor suggested other measures such as banning sugary snacks in schools would not be as effective as fluoridation even if they could be introduced.
Mr Laing said the Local Government Act also empowered the council to fluoridate the water supply and regarding its safety, he said the Ministry of Health had reviewed scientific papers on fluoridation and also commissioned its own studies on the issue.
He said the merits of fluoridation had also been considered by other bodies over many years.
"As far back as 1957 a commission of enquiry [was held] and also [later] the New Zealand Human Rights Commission [considered fluoridation], so it's interesting it's come up again at this time."
"It was put to bed by the Royal Commission in the 1950's and by Privy Council case but now it's reared its head again."
Mr Laing said local councils had three separate duties relating to water supplies, including ensuring an area had an adequate supply of water.
"[And] to take all practicable steps to ensure water supply meets with the standards and to take all reasonable steps to ensure the water supply is wholesome."
Duncan Laing said nothing in that was contrary to fluoridating a local water supply.
He also rejected the appellant's claim that the fluoride used in water supplies could contain a whole range of nasty chemicals.
"The drinking water standards are a very comprehensive set of standards as to what can be put into drinking water and it's simply not credible to say there will be dangerous quantities of these other trace elements [such as cadmium and arsenic] from fluoride".
Mr Laing said the Council relied on the Court of Appeal's finding that fluoridation does not constitute medical treatment.
However he said if the Supreme Court ruled fluoridation was a medical treatment, then the Council stood by the High Court finding that the intrusion into a person's rights arising from adding fluoride to a drinking water supply was minimal.
The Court has reserved its decision.