Local councils have only achieved fluoride targets for drinking water 54 per cent of the time over the last 30 years, researchers from the University of Otago and the University of Canterbury have found.
Dr Tim Chambers, a Senior Research Fellow at the University of Otago, Wellington, says even the best performing water supply only achieved fluoridation targets 78 per cent of the time. The failures were largely from adding too little fluoride to the drinking water. In very rare cases (0.2 per cent of the time) too much fluoride was added.
“We found major inconsistencies in terms of how well each council fluoridated its drinking water supply. Council compliance with achieving fluoridation has clearly been inadequate for the last 30 years.”
In general, larger water suppliers were more likely to achieve the targets than smaller suppliers, while city councils outperformed district councils.
The researchers analysed fluoride-testing data from 25 water suppliers serving more than two million people for the years from 1992 to 2022. However, 80 per cent of the data is from 2010 onwards due to lost data, which Dr Chambers says reinforces the need for a national database of drinking water quality to be set up.
Their research is published in the Journal of Public Health Dentistry.
It follows revelations by Wellington Water in 2022 that it had not been fluoridating Wellington's water supplies for almost a year, while dosing had been inconsistent for almost four years because of problems with faulty equipment.
Dr Chambers says the Wellington failure demonstrates that even some of New Zealand's largest and most well-resourced councils have been unable to consistently maintain fluoridation schemes across the country over the last 30 years. The failures are largely caused by ageing infrastructure as well as an over-reliance on manual make-up systems and monitoring.
“Wellington Water is one of New Zealand's largest water suppliers controlling water assets worth $6.1 billion, with an annual operating budget of $225 million. This suggests smaller water suppliers are likely to be struggling with the challenge of fluoridating their water supplies, given the need for ongoing maintenance and expert technical support.”
New Zealand water supplies have naturally low fluoride levels, and adding fluoride to drinking water is accepted as an effective and efficient way to prevent tooth decay and potentially avoidable dental-related childhood hospitalisations.
Water suppliers are required to conduct weekly tests for fluoride under national drinking water standards regulations, but are not required to report test results below the maximum acceptable value of 1.5 parts per million to the Ministry of Health.
Dr Chambers says self-regulation by councils of fluoride dosing is clearly not working.
“Our results suggest very few local councils are adhering to the voluntary code of practice for community water fluoridation. There is no obligation to implement the code of practice, nor is there any central oversight of water supplier performance against oral health targets.”
Dr Chambers says the government needs to make the code of practice mandatory and introduce central oversight of local councils' performance in achieving fluoridation targets for oral health by Taumata Arowai, the new national water regulator.
A standardised quality assurance system is also needed to ensure there is adequate monitoring, verification of fluoride testing results and corrective actions when there is over or under dosing, he says.
“Taumata Arowai must set up a national database of drinking water quality so the performance of water suppliers can be monitored. Without central oversight, it will be impossible for there to be a robust assessment of councils' performance in providing this key public health intervention.”
The research paper, 'An assessment of compliance with optimal fluoride levels for oral health benefit by New Zealand drinking water suppliers' is published in the Journal of Public Health Dentistry.
For further information, please contact:
Dr Tim Chambers
Department of Public Health
University of Otago, Wellington
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