An assessment of compliance with optimal fluoride levels for oral health benefit by New Zealand drinking water suppliers

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.