Background Elemental fluorine is widely distributed in domestic drinking water, which may directly affect water quality and the safety of residents' drinking water, thus causing certain adverse human health effects.

Objective To understand the level and distribution characteristics of fluoride in domestic drinking water in Shiyan City, and to assess the health risk of fluoride in drinking water among different populations.

Methods The concentration of fluoride in domestic drinking water in Shiyan City was monitored from 2021 to 2023. Rank sum test was used to compare the differences in fluoride concentration by years, water collection periods, sampling types, water source types, disinfection methods, and regions, and Spearman's rank correlation was used to estimate the correlation between fluoride and other water physicochemical indicators. Based on the total drinking water intake and body weight parameters recommended for different age groups in the Chinese Population Exposure Parameters Handbook, the health risk of fluoride via drinking water among different populations was assessed using the health risk assessment model of the U.S. Environmental Protection Agency (US EPA).

Results A total of 894 water samples were collected from Shiyan City in 2021−2023. The fluoride concentration in the samples ranged from 0.015 to 0.920 mg·L⁻¹, with a median of 0.17 mg·L⁻¹, which was lower than the limit value of GB 5749-2022 Standards for Domestic Drinking Water (fluoride concentration ≤1.0 mg·L⁻¹). There were significant differences in fluoride concentrations between different years, water collection periods, water sample types, sampling types, water source types, disinfection modes and regions (P < 0.05). Regarding fluoride variation patters, a trend of first decreasing and then increasing over the years was identified; dry season was higher than wet season; top water＞finished water＞secondary water supply; among the different disinfection methods, the lowest concentration of fluoride was found in the water samples treated by chlorine dioxide, and the highest was in the non-disinfected water samples; among different water sources, the highest level was found in springs, and the lowest level in shallow wells; significant differences were also found among different regions . The Spearman's rank correlation results showed positive correlations of fluoride with total dissolved solids, sulphate, turbidity, total hardness, carbon tetrachloride, arsenic, iron, nitrate-nitrogen, chloride, copper, colour, and pH (P < 0.05); and negative correlations with oxygen consumption, ammonia nitrogen, manganese, lead, cadmium, aluminium, zinc, cyanide, chloroform, anionic synthetic detergents, mercury, and chromium (P < 0.05). The results of health risk assessment showed that the non-carcinogenic hazard guotient (HQ) of fluoride intake through drinking water ranged from 0.005 to 0.993, which were less than 1. The average HQ of fluoride in drinking water for children aged 6-9 years was 0.184, which was significantly higher than that for other age groups.

Conclusion The concentration of fluoride in drinking water in Shiyan City is at a low level; various factors such as water collection period, water sample type, and disinfection method affect the concentration of fluoride, and there is a certain correlation between fluoride and chlorides, sulphate & pH in the water; the non-carcinogenic risk of fluoride ingested by drinking water is at a negligible level, but it should be noted that the level of non-carcinogenic risk is affected by age, region, disinfection method, and other factors.