Comparison of fluoride concentration and ph levels in drinking water between rainy and dry seasons in Tláhuac, Mexico City.

OBJECTIVE: To compare seasonal variations in fluoride concentrations and their relationship with pH in drinking water from the Tláhuac borough during rainy and dry periods. MATERIALS AND METHODS: A descriptive cross-sectional study was conducted to evaluate fluoride concentrations and pH levels in drinking water during the rainy and dry seasons in the Tláhuac borough. Samples were collected from 53 neighborhoods and stored at 4 °C until analysis. Fluoride concentrations were determined using a potentiometric method with an ion-selective electrode, and pH was measured using a digital pH meter. RESULTS: A total of 106 drinking water samples from 53 neighborhoods were analyzed across both seasons. The overall mean fluoride concentration was 0.509 ± 0.154 ppm, and the mean pH was 7.25 ± 0.48. Fluoride concentrations were significantly higher during the dry season than during the rainy season (p ≤ 0.0001). Likewise, pH values showed a significant increase during the dry period (p ≤ 0.0002). Pearson correlation analysis revealed a positive association between higher pH values and increased fluoride concentrations (p ≤ 0.049). CONCLUSION: Dry-season conditions significantly increased both fluoride concentrations and pH levels in drinking water, highlighting the influence of hydroclimatic and geochemical factors on fluoride mobilization. These findings underscore the need for continuous seasonal monitoring and for considering pH as a key indicator in assessing the risk of fluoride exposure.