The debate over fluoride in water is set to heat up again this week.
Anti-fluoride in water campaigner Professor Paul Connett has arrived in New Zealand for a series of public meetings, while Auckland health authorities are speaking out to support fluoridation.
The chemistry professor has spent 17 years campaigning against fluoride being put into water.
"It's a bad medical practice to use the water supply to deliver medicine," says Dr Connett. "You can't control the dose, you can't control who gets the medicine and you are forcing it on people who don't want it."
But his view is opposed by the World Health Organisation and a majority of scientists, who say fluoridation is an effective way of reducing tooth decay.
More than half the New Zealand population is covered by councils who fluoridate their water.
"It is safe and effective and it benefits everyone across the population," says Dr Julia Peters of the Auckland Regional Public Health Service. "We are here about protecting the health of everybody in this region."
Dr Connett has been called a quack by some of his opponents online, but he says he just wants a proper debate.
"The evidence that it is causing harm is getting stronger by the day, and in particular I'm most concerned about the lowering of IQ," he says. "We now have 37 studies that indicate an association with lowered IQ."
Auckland health authorities say fluoride can cause fluorosis, or white spots on the teeth, but it is safe.
"The studies that have implicated adverse health effects have almost universally been of very poor quality," says Auckland medical officer of health Richard Hoskins.
Dr Connett's first speech is in Auckland on Tuesday. His visit could coincide with a ruling due out any day from the High Court on whether the South Taranaki District Council had the authority to introduce fluoride into its water system.