Newshub can reveal that every single council in New Zealand that fluoridates its drinking water is failing to do so at the proper level.
A new report shows councils are only putting correct doses of fluoride in the water 50 percent of the time which means more than one million Kiwis are missing out on its benefits of protecting their teeth.
Dentists are shocked and say it's resulting in more tooth decay, pain and suffering.
What you may not be aware of is that only 27 out of 67 councils in New Zealand fluoridate their water at all.
Gisborne Dentist Annie Van Wichen pulls rotten teeth out every day.
"Heaps and heaps of tooth decay. It's not uncommon to see teenagers needing multiple teeth removed and needing most of their teeth in mouth filled, same for adults as well. There is just a huge amount of need," she said.
She's shocked by new data showing Gisborne's low fluoridation levels.
"It's honestly quite distressing," Van Wichen said.
The city's water only has the right amount of fluoride 4.2 percent of the time.
"That's really concerning because there are so many people that could probably still have teeth if the water had been fluoridated," Van Wichen said.
Fluoride levels must be between 0.7 and 1 'parts per million' to prevent tooth decay.
Of our 67 councils, only 27 add fluoride to drinking water, Tauranga and Christchurch are the largest councils not fluoridating.
Dr Tim Chambers from Otago University's Department of Public Health gathered fluoride testing data from councils that fluoridate and found on average they only hit the target 54 percent of the time, meaning more than a million kiwis miss out.
"This is a major problem for us because that is a key public health intervention, and not having access to it has likely contributed to worse oral health," Dr Chambers said.
Of the councils currently fluoridating Gisborne is the worst at 4.2 percent. Also near the bottom is Thames at 11.9 percent and Huntly on 15.9 percent, while Invercargill reached its target 50.4 percent of the time, Wellington at 54 percent and Auckland is on 68 percent.
And although Dunedin takes the top spot at 77.9 percent - it still falls short.
The Associate Minister for Health Dr Ayesha Verrall isn't impressed.
"It's not good enough. That's why we 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.
Councils are not currently required to fluoridate - some are so small that it isn't feasible - and there are a number of reasons why some councils don't reach the optimal level.
"To avoid too much fluoride being in our water supply, and to achieve regulatory compliance, we have set an operational target which is half the Maximum Acceptable Value," Gisborne District Council's Community Lifelines Director David Wilson said.
He said the council will now improve its fluoridation levels.
But councils are on notice. Fourteen have been ordered to fluoridate within the next three years and the minister said a new monitoring regime will soon be in place which will include penalties of upto $200,000 for local authorities that don't comply and meet the standard.
But experts say that's not enough - they want to see the government collecting better drinking water data.
"We need to implement the national database, to make the code of practice mandatory, and to ensure oral health targets are part of the regulation", Dr Chambers said.
Which could mean dentists are pulling fewer rotten teeth.
The Three Waters reform is expected to help this fluoride problem because with four entities, rather than 67 individual councils doing their individual thing, and Dr Chambers said it should reduce the inconsistencies.
"It enables the consolidation of the limited fluoridation expertise and enables greater availability of capital to purchase and maintain fluoride schemes," he said.
Rob Beaglehole from the Dental Association is appalled by the report, saying it highlights the need for a water reform.
"We really need the Three Waters to sort out this mess. It doesn't make any sense for 67 councils to look after 67 different water supplies."
Local Government NZ CEO Susan Freeman-Greene said they are pleased the decision-making powers for fluoride are with the Director General of Health, but there are some concerns.
"While the Ministry of Health has provided some funding for councils to cover capital costs associated with fluoridation, it remains a concern that some of our smaller councils will struggle with the operational costs and getting the specialist staff required," she said.