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An assessment of compliance with optimal fluoride levels for oral health benefit by New Zealand drinking water suppliers.
Abstract
Objectives
Community water fluoridation (CWF) has proven oral health benefits. We investigated whether drinking water suppliers are meeting New Zealand CWF targets (0.7–1.0 ppm) to ensure these benefits.
Methods
We retrieved fluoride testing data from 25 supplies serving 2,059,000 people (82% of people on a fluoridated supply), for the years 1992–2022 (22,220 weekly observations). We descriptively assessed compliance with fluoride targets in this convenience sample.
Results
The mean fluoride level was 0.66?ppm (SD 0.28). Water suppliers achieved fluoride targets 54.1% of the time (range 4.2%–77.9%). Fluoride concentration fell short of the target in 42.2% of observations, exceeded but under the maximum acceptable value (MAV) in 3.6%, and in excess of the MAV in 0.1%. The percentage of compliant observations was greater in larger than smaller supplies.
Conclusions
Noncompliance with CWF targets was common. Epidemiological studies that rely on fluoridation status as their exposure may underestimate the oral health benefits of CWF. Our results highlight future challenges with the feasibility of expanding CWF under new legislation as well as the weaknesses in drinking water surveillance.
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INTRODUCTION
Community water fluoridation (CWF) has proven benefits for oral health and promotes health equity [1]. New Zealand (NZ) city and district councils are local government authorities that supply 98% of all drinking water to people on a reticulated water supply (85% of the population) [2]. NZ water supplies almost universally have naturally low-fluoride levels. Twenty-seven of 67 councils currently fluoridate at least one water supply in their jurisdiction, supplying water to ~2.5million people (50% of the population) [3].
A 2015 costing of extending fluoridation to nonfluoridated areas in NZ was estimated at $144 million over a 20-year period, with a net savings of $600 million [4]. Subsequently, NZ introduced the Health (Fluoridation of Drinking Water) Amendment Act 2021, which moved fluoridation decisions from councils to the Director General of Health, with the intention of expanding CWF to nonfluoridated regions of the country [5]. However, no legislative analysis or available NZ evidence has examined water suppliers’ ability to consistently achieve fluoride levels required to improve oral health, with the exception of one study from Dunedin which found observed fluoride concentration from one council at a mean of 0.74 parts per million (ppm), with values ranging from 0.63 to 0.85?ppm [6]. Internationally, one systematic review of 14 Brazilian studies found that mean fluoride levels in city supplies ranged from 0.17 to 0.89?ppm, and levels were outside the target range for 56.6% (95% CI 45.5; 67.3) of measurements [7]. In the United States (US), some fluoride data from the US Fluoridation reporting System (WFRS) is publicly available via the Centers for Disease Control and Prevention web interface [8]. A quick analysis of Californian state fluoridation supplies from 2018 show that supplies met CDC optimal fluoride targets (0.6–1.0 ppm) 95% of the time, however, 23% of all observations were missing [9].
In NZ, monitoring and reporting requirements for fluoride in drinking-water are based on compliance with the maximum acceptable value (MAV) of 1.5 ppm outlined in the Drinking-Water Standards for New Zealand (DWSNZ) [10], not the optimal levels for oral health (0.7–1.0 ppm). Water suppliers are required to test for fluoride weekly under the DWSNZ [10] but are not required to report test results below the MAV to the Ministry of Health (MoH), and a national longitudinal database for drinking water quality is not available in NZ [11]. NZ has a voluntary Code of Practice for CWF (COP); however, it is unclear how many water supplies adhere to the COP. [12]. Consequently, water suppliers effectively self-regulate the fluoridation of their supplies for oral health purposes.
Water supplier compliance has implications for assessing epidemiological evidence, the current state of CWF infrastructure and the feasibility of policy changes. The aim of this short report is to assess water supplier compliance with recommended fluoride levels (0.7–1.0 ppm) in a convenience sample of fluoridated areas of NZ.
METHODS
In March 2022, we sent official information requests to all 67 councils for water quality data as far back as records permit. At the time of publication, of 67 councils have yet to complete the request (response rate 88% among all councils; 70% response rate among fluoridating councils). All weekly fluoride test data were provided in Excel files which were collated into a single database. The data were provided at the treatment plant level (some supplies have multiple treatment plants). Data were analyzed at the water supply level so treatment plant data were aggregated within each water supply. Compliance with oral health targets was defined as any fluoride measurement from 0.7 to 1.0 ppm. Population size was based on the number of people served by a water supply according to the MoH database of registered supplies. To determine the impact of population size on fluoride compliance we used beta regression. Population size was treated as a categorical variable based on MoH water supply definitions small =?<5000; medium 5000–9999; and large ?10,000 and binary variable using council definitions: either a city council which are generally large metropolitan areas or a district council which are generally smaller populations, rural and/or cover large areas. Descriptive statistics and regression results were generated in Stata V17.0 (StataCorp LLC, College Station, TX).
RESULTS
In total, we received data from 25 water supplies serving 2,059,000 people (82% of people on a fluoridated supply), including 22,220 weekly observations from 1992 to 2022 (Table 1). The mean fluoride level was 0.66?ppm (SD 0.28) across 25 fluoridated water supplies (Table 1). Water suppliers achieved fluoride targets 54.1% of the time overall, while individual water supply compliance percentages ranged from 4.2% to 77.9%, with an interquartile range of 14.2%–54.6%. Nearly half of observations (42.2%) were under targets (<0.7 ppm), 3.6% were over targets but under the MAV (>1.0 & <1.5 ppm), while 0.1% exceeded the MAV (?1.5 ppm). Large supplies had higher fluoride compliance percentage than smaller supplies but not medium sized supplies, while city councils outperformed district councils.
Implications for policy
NZ’s Health (Fluoridation of Drinking Water) Amendment Act 2021 is intended to result in wider adoption of CWF across NZ. Our results shed some light on council capacity to implement and maintain effective CWF schemes, which were not visibly considered in the original policy and regulatory impact assessments [3, 17]. These preliminary results suggest that the costs of CWF may be higher than anticipated if existing costings assumed 100% compliance, [4] particularly for smaller supplies. This is a serious concern as one of the three criteria for fluoridation decision-making under the new Act is:
“the likely financial cost and savings of adding fluoride to the drinking water, including any additional financial costs of ongoing management and monitoring.” [5], p. 4.
Some of NZ’s largest, most resourced councils have been unable to consistently maintain fluoridation schemes across the country – primarily due to the implications of aging infrastructure [13]. It appears unlikely central Government will cover the expected cost of additional fluoridation. The 2015 report prepared for the MoH estimated expanding fluoridation schemes would cost $144?m over 20?years (assuming current schemes were 100% effective) [4], while central Government has proposed initial financial support of $8.3 m, plus another $3 m per year ($68.3 m over 20?years). However, price inflation over the past 7?years will exacerbate this resourcing deficit, for example, the cost of fluoridating Christchurch City’s water supply is estimated at $60?m, plus $2.5 m annual operating costs. The resourcing deficit will likely widen oral health inequities as more affluent areas will likely have greater capacity to effectively implement schemes.
Our results support the regulatory implementation of the NZ COP. Specifically, the requirement to implement a standardized quality assurance system that ensures adequate monitoring, verification of the fluoride testing results and corrective actions in the event of over- or under-dosing [12]. Clearly, in NZ, either the quality assurance systems implemented under the voluntary COP are inadequate or suppliers are not upholding the code. Mandatory implementation of the COP will also bring important improvements in health and safety procedures and system design and performance.
The scarcity of data to inform policy decisions on fluoridation is attributable to the MoH’s failure to collect, store and maintain a national database of drinking water quality for public health surveillance. Responsibility for drinking-water regulation has recently been transferred to a new independent water regulator, Taumata Arowai, who is currently consulting on new drinking water standards and compliance rules. However, Taumata Arowai have yet to publicly commit to developing or maintaining a national database of drinking-water quality. Without such a commitment, NZ’s fragmented and data-poor approach to public health surveillance and drinking water is likely to continue [11]. Further, without central oversight, the existing approach of council self-regulation that has obscured robust assessment of their performance and the provision of a key public health intervention will continue.
CONCLUSION
Most NZ water suppliers have not consistently achieved fluoride levels necessary for oral health benefits. Consequently, epidemiological studies using exposure assessments reliant on fluoridation status may be underestimating the true oral health benefits of CWF. The failings of water suppliers also highlight some concerns for the new Health (Fluoridation of Drinking Water) Amendment Act 2021 to consider and the need for Taumata Arowai to create and maintain a national dataset of drinking water quality. Our results demonstrate the need to update and incorporate the Code of Practice into legislation or regulation, with central oversight from the new water regulator, Taumata Arowai.