Fluoridated Water For Half A Million More Kiwis – Expert Q&A

Thursday, 10 April 2025, 11:17 am
Press Release: Science Media Centre

Local authorities in Rotorua and Whangarei are now complying with directions to fluoridate community drinking water.

It means that over 500,000 people in Aotearoa have gained access to fluoridated water since July 2022.

These comments have been excerpted - read the full versions on our website.

The SMC asked local and international experts about what this might mean for public health, and the science around fluoridation. Feel free to use these comments in your reporting or follow up with the contact details provided.

Professor Philip Schluter, Professor of Population Health, School of Health Sciences, University of Canterbury, comments:

What long-term changes can we now expect in dental disease rates?

"Community water fluoridation has been hailed as one of the greatest public health achievements of the 20th century. It provides an equitable and cost-effective system of fluoride delivery to communities within Aotearoa | New Zealand and across the globe.

"According to the USA’s Centers for Disease Control and Prevention, the introduction of community fluoridated water decreases tooth decay in children by at least 40% and tooth loss in adults by at least 40%. In a recent nationwide study of children here, we found a reduction of severe tooth decay by more than 20% in those living in fluoridated areas compared to their non-fluoridated peers. This is despite claims by some that ‘people don’t drink water these days’ or that it is unnecessary due to the frequent use of fluoridated products like toothpaste and dental care. I have not met a parent or child with severe tooth decay (a largely preventable condition) who thought that severe tooth decay is a good outcome and that community water fluoridation was a bad idea.

"With Rotorua and Whangarei councils now complying with fluoridation orders, this means that over 500,000 people have gained access to fluoridated water since 2022. As the public benefits of water fluoridation are clear and well-established, based on the strongest scientific evidence available, people in these communities will have improved oral health in their future – as measured on a population level."

What does this mean for Aotearoa's public health system?

"There will also be flow on public health effects, with reduced demand on acute services and extractions of teeth needed under general anaesthesia in our already stretched clinics and hospitals. This is cause for celebration."

What does the current evidence say about the effects on the average person of drinking fluoridated water?

"There are some studies reporting negative effects of community water fluoridation, including lowering IQ and increasing neurodevelopmental disorders and thyroid function issues. Unlike the evidence for community water fluoridation, these studies lack the same repeatability or rigour.

"A 2024 meta-analysis and systematic review conducted by the Ministry of Health concluded that there is no causal link between fluoride exposure at the levels used in Aotearoa | New Zealand for community water fluoridation and significant harm to health. Meta-analyses and systematic reviews bring together ALL available evidence and syntheses their findings. These are regarded as the highest form of scientific evidence in populations. This 2024 conclusion is consistent with previous Aotearoa | New Zealand reviews conducted in 2014 and 2021."

How do added fluoride levels compare to naturally occurring levels of fluoride in water?

"In Aotearoa | New Zealand, the natural levels of fluoride in groundwater are generally low, typically around 0.1-0.2 parts per million (ppm). Community water fluoridation increases these natural levels to 0.7-1.0 ppm, in line with international recommendations. The only known adverse effect of fluoridation at this level is mild dental fluorosis, characterised by opaque white spots in the enamel. But, based on all the evidence, it was concluded in the 2014 review that: “The risk for mild fluorosis that is associated with fluoride exposure is highest for formula-fed infants, and young children who are likely to swallow toothpaste. In some cases the fluoride intake by these groups can approach or exceed the currently recommended conservative upper intake level, but the rarity of cosmetically concerning dental fluorosis in New Zealand indicates that such excess intake is not generally a safety concern.”"

"As we observed in our NZMJ paper, right now, almost one in every five children in Canterbury (which is unfluoridated) has severe tooth decay. This and other largely preventable oral diseases are likely to have consequences reaching far into the affected children’s and societies’ futures. Moreover, two in every five Pacific children and over one in every four Māori children aged five years have experienced severe tooth decay, reinforcing the gross inequity patterns previously observed both locally and globally. All our children deserve better. And community water fluoridation is a giant step in that direction."

Conflict of interest statement: No conflicts of interest.

Dr Tule Misa, President of the Pasifika Dental Association, General Dental Practitioner and Public Health Dentist, Acting Clinical Director Community Dental Service Canterbury, comments:

What long-term changes can we now expect in dental disease rates?

"We know that water fluoridation is safe and cost effective and it benefits all people regardless of their social status. Pacific families and Maori families, and low socioeconomic status individuals, are the most vulnerable populations to dental decay. Water fluoridation will help them reduce their rate of dental caries as the fluoride will strengthen their teeth and prevent dental decay.

"Water fluoridation is a public health measure to prevent dental decay and this will help reduce the inequity in oral health outcome for Pacific and Maori whanau.

"In 2015, the Ministry of Health commissioned the Sapere Research Group to examine the benefits and costs of community water fluoridation.

"The Sapere Report reviewed both New Zealand and international evidence. It estimated the benefit of water fluoridation as follows:

• 40% lower lifetime incidence of tooth decay among children and adolescents
• 48% reduction in hospital admissions for the treatment of tooth decay among children aged 0-4 years
• 21% reduction in tooth decay among adults aged 18–44 years
• 30% reduction in tooth decay among adults aged 45 years and over."

What does this mean for Aotearoa's public health system?

"When dental caries is reduced it will help the public health system saving lots of money from dental treatment needed for children who have dental decay. Every dollar spent on water fluoridation will save around $9 in dental care costs.

"Last thing to say, Pasifika Dental Association fully supports the Community Water Fluoridation scheme as it is a safe and effective public health intervention to prevent dental caries for all people including our Pacific families."

Conflict of interest statement: No conflicts of interest.

Professor Sheila Skeaff, Department of Human Nutrition, University of Otago, comments:

How do added fluoride levels compare to naturally occurring levels of fluoride in water (or other sources like tea)?

"There is fluoride in the water that comes from rivers, lakes, wells, springs and reservoirs in New Zealand, but typically at a very low level (<0.15 mg/L). New Zealand has a lower level of fluoride in the water than many other parts of the world partly because the amount of fluoride in our soil is lower.

"Fluoridation increases (tops up) the amount of fluoride in water to 0.7 to1.0 mg/L. This is the amount of fluoride found in the water in places where soil fluoride is naturally higher. A cup of fluoridated water would provide 0.18-0.25 mg of fluoride.

"It is possible to have too much fluoride in drinking water. An increase in the fluoride level in the water can occur naturally (e.g., volcanic activity) or from pollution (e.g., burning coal, fertilisers, aluminum smelters). Given this, it is important to routinely measure the fluoride content of drinking water in New Zealand.

"The tea plant naturally accumulates fluoride. Some black teas, even when prepared with deionised distilled water (i.e., highly filtered non-fluoridated water), can contain 10 times more fluoride than a cup of fluoridated water. In New Zealand adults, tea makes the largest dietary contribution (60-80%) to total fluoride intakes."

What do we know about how much fluoride the average person gets in Aotearoa?

“Fluoride was included in the 2016 New Zealand Total Diet Study. Various issues in analysing the fluoride content of some foods means that the estimated intake of fluoride from the Total Diet Study is likely to be underreported.

“A few dietary studies conducted in the Department of Human Nutrition at the University of Otago found that fluoride intakes in children and adolescents were lower than recommended, and highlighted the important contribution of fluoridated water to fluoride intakes of young people in New Zealand. None of the young people in these studies were close to consuming fluoride above the upper limit."

Conflict of interest statement: No conflicts of interest.

Associate Professor Matthew Hobbs, Adjunct Researcher in the Faculty of Health, University of Canterbury, comments:

What long-term changes can we now expect in dental disease rates?

"Our own research has shown that water fluoridation was related to a reduced dental-related hospitalisation rate for children aged 0–4 and 5–12 years. Importantly, children living in the most deprived areas showed the greatest benefit from water fluoridation for dental-related hospitalisation rates. This indicates that the greater health gain from water fluoridation occurred for those with the highest socioeconomic disadvantage and most need."

How do added fluoride levels compare to naturally occurring levels of fluoride in water (or other sources like tea)?

"[...] Our research has recently shown that the levels of fluoride in community water are below where they need to be. In a 2023 study, we retrieved fluoride testing data from 25 supplies serving approximately 2 million people (82% of people on a fluoridated supply), for the years 1992-2022 (22,220 weekly observations). We descriptively assessed compliance with fluoride targets. Results showed the mean fluoride level was 0.66 ppm. However, water suppliers achieved fluoride targets 54% of the time (range 4%-78%). Fluoride concentration fell short of the target in 42% of observations. The percentage of compliant observations was greater in larger than smaller supplies. We concluded that this meant that noncompliance with water fluoridation targets was common and that any epidemiological studies that rely on fluoridation status as their exposure may underestimate the oral health benefits of water fluoridation."

Conflict of interest statement: No conflicts of interest.

Dr Justin Wall (Te Rarawa, Te Aupōuri), tumuaki of Te Rōpū Niho Ora and practising dentist, comments:

With over 500,000 New Zealanders gaining access to fluoridated water since July 2022, what long-term changes can we expect in dental disease rates?

"The benefits from fluoridation is much greater than you'd expect. While many people don't have any dental decay, those who do will see a significant impact. There is a lot of talk about the benefits to children, but the benefits are to everybody at all ages.

"During the course of the day, the pH in your mouth drops, becoming more acidic, and you start losing enamel - the outer mineral layer of your teeth. Your saliva helps it to recrystallise. When you eat, the pH goes back up, then drops again, and this is a constant cycle. Fluoride helps create much denser crystals, making the enamel stronger. If enough fluoride is available, the pH in your mouth has to be a lot more acidic to dissolve your teeth. This doesn't just affect children, it affects everyone.

"The population of New Zealand is ageing, and the rate of tooth decay in the elderly is of significant concern. A lot of them may be medically compromised or unable to afford dental work. Our ageing population have done what they were asked to do - looked after their teeth - but are now in a position to need the extra protection from fluoride.

"Poor oral health also increases the risk of problems in the jaws in the management of osteoporosis, and means we need to use more bisphosphonate drugs to improve bone density in our aging population."

How might this affect rates of other health conditions linked with tooth decay?

"We work with a number of people with co-morbidities, and any public health process that can lessen the burden on this vulnerable group is to be promoted.

"For example, one of the consequences of diabetes is an increased risk of gum disease, while uncontrolled diabetes will cause dry mouth and increase risk of tooth decay. Gum disease and tooth decay make managing your health far more difficult, and I have seen this firsthand in clinical practice. The inflammation caused by oral infections makes diabetic control more brittle – and reducing the burden of oral sepsis improves diabetic control.

"Inflammation is a risk factor for cardiovascular disease and chronic inflammatory conditions, and oral infection is a major cause of this. The resulting oral sepsis is major contributor to this systemic burden - when patients with oral infections say they feel unwell, it is because they are."

What does this mean for Aotearoa's public health system?

"Every general hospital admission for dental reasons costs upwards of $6000, and ninety percent of the work done by New Zealand's mobile surgical bus is dental. Fluoridation improves oral health, which reduces the cost of systemic health."

Should people in areas with fluoridated water keep using fluoridated toothpastes?

"You should keep using fluoridated toothpaste. This isn't going to cause problems. Fluorosis, which people get concerned about, is a flecking of teeth, but that's actually how the role of fluoride was first discovered in the US, where people in a town were found to have brown flecked teeth but no tooth decay. This was linked to naturally high fluoride levels in the water. At lower levels, it still prevented decay but didn't cause fluorosis - and these are the levels fluoride supplementation to water is based on."

No conflict of interest declared.

Professor Oliver Jones, Professor of Chemistry, RMIT University, Melbourne, Australia, comments:
 

What long-term changes can we now expect in dental disease rates?

"I expect that, over time, we will see a large decrease in dental decay and cavities, as has been seen in other countries after water (or milk or salt in some countries) is fluoridated. For example, today, around 90% of Australians have fluoridated water (although it varies by state; 28% of Queenslanders do not have fluoridated water). This is estimated to have reduced tooth decay in Australia by 26–44%, regardless of socioeconomic status.

"The first city in the world to fluoridate its drinking water was Grand Rapids, Michigan, in the USA; cavity rates in children born in the town dropped by more than 60% after fluoridation. Indeed, the fluoridation trials to set this up were discontinued after six years because the benefits to the children in the fluoridated community were so clear that it was deemed unethical not to provide them to everyone.

"I think this change will do a lot of good in New Zealand."

What does this mean for Aotearoa's public health system?

"If dental decay goes down, so do all the associated problems and the costs of treating them. This could save Aotearoa's public health system a lot of money - which could then be put to good use elsewhere. Research from the USA showed that for every US$ spent on fluoridation, communities save about US$20 in dental treatment costs due to fewer fillings, extractions, and emergency visits. This is a pretty good return on investment."

How do added fluoride levels compare to naturally occurring levels of fluoride in water (or other sources like tea)?

"This varies depending on where in the world you are. The amount of fluoride added to water is generally enough to get the concentration of fluoride to between 0.5–1.5 mg/L to get the benefit to teeth. In most places, the levels of background fluoride are much lower than that, so fluoride must be added. In some parts of the world, the natural background levels are much, much higher, so must diluted down to avoid harm.

"Levels of fluoride in tea can be higher than in drinking water because the tea plant can absorb fluoride from the soil it is grown in. The final concentrations vary depending on the type of tea, where it was grown, how it was brewed, etc. However, they are still not likely to be harmful. We tend to drink relatively small amounts of tea compared to water, so a direct comparison is not that useful. Context matters in toxicology."

What does the current evidence say about the effects on the average person of drinking fluoridated water?

"The current evidence (and there is a lot of it) is that the only effects on the average person of drinking fluoridated water (or the Fluoridated milk or salt used in some countries) are reduced dental decay. It has been shown time and time and time again that the amount of fluoride in water is not high enough to cause harm, even considering other sources of fluoride we might encounter, such as toothpaste and even tea.

"Many critics are quick to cite a 2019 study that claimed fluoride affected the IQ of children. However, this work was roundly criticised at the time, and serious weaknesses were identified in the study design. More robust studies, including one from New Zealand that followed people over thirty years, found no association between fluoride intake and IQ.

"It is true that excessive fluoride intake can cause adverse health effects such as skeletal fluorosis (a disease leading to weakened bones), and neurological effects, but the key word here is ‘excessive’. The amounts needed to cause such effects are orders of magnitude higher than what is added to water. Remember, everything is toxic in the right amount, even water itself. Discussions about toxicity are meaningless with context. Too much alcohol will give you liver damage, for example, but that doesn’t mean we ban alcoholic drinks."

Are there risks associated with fluoridation and lack of fluoridation?

"Water fluoridation can be a contentious issue and there is a lot of misinformation about it online. Some people fear overreach by the government or health providers, and some say even if the risk is low, why not just be safe? Governments are not perfect, but why would they add something to the water they knew was harmful? What would be the benefit, especially when they drink the same water?

"Dentists are also often accused of somehow being in with ‘big fluoride’. But dentists make their money from fixing your teeth. Fluoride reduces cavities, so if dentists just wanted your money, they would surely be keen to remove fluoride from water – not add it.

"Similarly, when we talk about risk, we should remember that nothing is risk-free. For example, if I drive a car, I might crash; if I go for a swim, I might drown. I still drive and swim.

"We also need to think about the risks of not fluoridating water. In 2015, the city of Buffalo, New York, removed fluoride from its water supply. Dental problems increased so much that parents sued the city for harming their children and to get the fluoride back. Calgary, Canada, removed fluoride from drinking water in 2011. Seven to eight years later, dental cavities in children were significantly higher in Calgary compared to nearby Edmonton, which did not remove fluoride. Similarly, the introduction of nationwide water fluoridation in Israel in 2002 significantly reduced children's dental issues. However, this trend reversed in 2014, when Fluoridation was discontinued even though free dental care for children was introduced at the same time to compensate."

Conflict of interest statement: "I have no direct conflicts of interest to declare. I have previously received funds from various Australian Water utilities for research into environmental pollution, though not for fluoride."

Associate Professor Matt Hopcraft, Associate Professor in Professional Practice, Melbourne Dental School, The University of Melbourne, Australia, comments:
 

What long-term changes can we now expect in dental disease rates?

“Since 2022 more than 500,000 New Zealanders have gained access to fluoridated drinking water, which is an important step for public health. It is even more important in the face of a growing movement to take fluoride from water supplies in the USA and Australia which will inevitably lead to poorer oral health outcomes.

“Given that one in two New Zealand children experience tooth decay by the time they start school, proven measures that help to reduce this burden of disease at the whole population level are critical.”

Conflict of interest statement: Dr Hopcraft was formerly CEO of the Australian Dental Association Victorian Branch, and consulted to Oral-B and Haleon.

Associate Professor Virginia Dickson-Swift, Principal Research Fellow, Violet Vines Marshman Centre for Rural Health Research, La Trobe University, Australia, comments:

What long-term changes can we now expect in dental disease rates?

"I am active in the water fluoridation advocacy space in Australia (and more particularly in rural Australia where many of our smaller towns don’t have fluoride in the water as yet).

"In Queensland they have now left it up to the local councils and in some places they have removed the fluoride from the water and we can see the impact of that on potentially preventable hospitalisations (particularly in children) and rates of dental disease (both increasing). A good example is Cairns, where the fluoride was removed, who are now seeing an increase in preventable hospital admissions for dental (for example 2022-23, Queensland Health data shows 4,137 children aged 10 and under were admitted to Queensland hospitals for dental caries – up from 3,704 the previous financial year)."

Conflict of interest statement: “No conflicts of interest. I am a principal research fellow and lead a stream of oral health research and am active in the water fluoridation advocacy space in Australia”.

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