But the director-general of health is maintaining there are "no adverse health effects" in adding fluoride to NZ drinking water.
Ten days ago, in a US federal court decision, a Californian judge ordered the US Environmental Protection Agency (EPA) to strengthen regulations for fluoride in drinking water.
Reuters reported the finding as saying fluoride posed an unreasonable potential risk to children, at the levels typically used in the US.
US District Judge Edward Chen sided with several advocacy groups, finding the current US practice presented an unreasonable risk for the developing brains of children, Reuters said.
But the judge also stressed he was not concluding with certainty that fluoridated water was a danger to public health.
Fluoride Free Waitaki spokeswoman Sheryl Black said the decision cast enough doubt.
"I call on our council to turn off fluoridation immediately as a sensible precaution, and not least because [it] has a statutory duty to protect the public under the Health Act," Ms Black said this week.
Waitaki has been dosing both the Oamaru and hinterland water supply since July, following a compulsory order from the director-general of health.
Waitaki Mayor Gary Kircher said the council was aware of the US court development but it would "just follow the law" in the meantime.
"At the moment, it’s still in the hands of the director-general.
"There’s nothing overall that says it’s definitely harmful or not harmful," he said.
According to Water NZ, the US EPA sets a maximum acceptable concentration for fluoride in water supplies of 2.0mg/L (2 parts per million).
This is higher than the 1.5mg/L set in New Zealand.
The Waitaki District Council is dosing its Oamaru and surrounding areas water supply at between 0.7mg/L to 1mg/L.
The council has previously considered risking a $200,000 fine plus $10,000 a day for not complying.
Ms Black said the council should defy the compulsory order.
"I don’t believe the courts would fine Waitaki District Council for adopting a sensible precautionary approach and turning off the fluoride until the matter is settled.
"It’s unlikely a court could say they were acting improperly — especially since the [director-general] of health has still not completed her Bill of Rights analysis explaining why it would be justifiable ... to force Waitaki citizens to take this supposed ‘medication’ against their will."
The ministry said it was aware of the recent US decision.
Meanwhile, the directions to fluoridate remained in place.
A spokesman said the director-general, Dr Diana Sarfati, was working on the requirement ordered by the High Court that she consider the Bill of Rights in making the fluoride directive.
"The director-general is undertaking a Bill of Rights analysis of the directions to ensure that section 11 of the New Zealand Bill of Rights Act 1990 is considered.
"The [fluoride] directions remain in place in accordance with High Court rulings," the ministry said.
The World Health organisation "and other international and national health and scientific experts" had endorsed water fluoridation "as an effective public health measure".
This included a 2014 Royal Society paper in conjunction with the chief scientific adviser to the prime minister concluding there were "no adverse health effects".
Reuters reported the non-jury trial leading to the US decision established that fluoride posed an unreasonable risk of harm sufficient to require a regulatory response by the EPA.
"The scientific literature in the record provides a high level of certainty that a hazard is present; fluoride is associated with reduced IQ," Judge Chen wrote in his decision.
Reuters said the USA EPA was now reviewing that decision.
