Three Waters will ensure fluoride is correctly added to water supplies, NZ Dental Association hopes

Children's teeth are the main victim of councils' failings to correctly add fluoride to water supplies, the NZ Dental Association says.

A new report obtained by Newshub revealed councils weren't fluoridating water properly, with some only having correct levels for 4 percent of the year - meaning more than 1 million Kiwis are missing out on the benefits of fluoride. 

Dental Association spokesman Rob Beaglehole said councils were lacking when it came to protecting the health of children.

Dr Beaglehole told AM the association is "hoping" Three Waters, the Government's contentious plan to set up four public entities to be responsible for water supplies instead of the country's 67 councils, would help. 

"What we know is it doesn't matter whether the councils or the Government add or the Three Waters add the fluoride to the water supply - anybody with teeth is going to benefit from water fluoridation," Dr Beaglehole said.

"Ideally it would [help] - instead of 67 councils having to fluoridate their water supply, there will only be four entities so we're hoping this will streamline the process."

Appearing on Newshub Late on Thursday, health science professor Philip Schulter said even the smallest amounts of fluoride provided protection - but councils should get back to optimal numbers for maximum results.

Fluoride levels must be between 0.7 and 1 'parts per million' to prevent tooth decay. 

"If we were fluoridating appropriately and within the guidelines, we'd have the maximum reduction in rotten teeth," said Schulter, from the University of Canterbury.

"Because we're not, that means we have higher rates - or higher likelihood - than I guess we were hoping for."

Associate Health Minister Ayesha Verrall said it wasn't good enough. That's why the Beehive "changed the law to allow central Government to direct councils to fluoridate, and set that they have to do so at an acceptable level", Dr Verrall said.

Earlier this year, fourteen councils were ordered to fluoridate within three years by then-Ministry of Health chief Ashley Bloomfield.