Abstract This study analyzed the relationships between the concentration of natural fluoride in public water supply and meteorological and hydrographic factors in a northeastern region of Brazil. This was a descriptive, analytical, ecological, longitudinal, and field study conducted by collecting water in 23 municipalities (2019 to 2020) of four macroregions of Paraíba (Brazil): coast (1), borborema (2), agreste (3), and outback (4). Four collection sites were selected per municipality: two near and two distant from the water treatment plant. Fluoride concentration was determined using a combined ion-specific electrode and classified according to the Collaborating Center of the Ministry of Health in Oral Health Surveillance. Meteorological, hydrographic, and population characteristics were also collected. All analyzed samples showed natural fluoride; macroregions 2 and 4 showed the highest mean fluoride concentration, macroregion 4 presented the highest mean temperature, and all macroregions showed a similar pattern of precipitation. The mean fluoride concentration of the four macroregions was below the appropriate value to prevent caries. An increase in precipitation would decrease the fluoride concentration in water. In conclusion, the concentration of natural fluoride varied according to meteorological and hydrographic factors. The concentration in surface waters increased during periods of low precipitation. Therefore, this study provided important information to support implementation of community water fluoridation in this region.

Resumo Introdução A fluoretação das águas de abastecimento público é uma medida importante na prevenção à cárie dentária. Objetivo O objetivo do presente estudo foi avaliar e monitorar os teores de flúor nas águas de abastecimento público em um município de pequeno porte no Nordeste do Brasil. Material e método O estudo apresenta uma abordagem quantitativa de caráter descritivo. Foram selecionados 3 pontos para realizar coleta das águas duas vezes no mês na zona urbana do município durante 12 meses. A concentração de flúor foi obtida pela média das três leituras das amostras analisadas para cada ponto de coleta e classificadas conforme critério proposto pelo Centro Colaborador do Ministério da Saúde em Vigilância da Saúde Bucal. Resultado Segundo o critério utilizado (0,55 – 0,84 mg/L F), apenas 9,7% das amostras estavam dentro do considerado ideal. Conclusão Observou-se que a fluoretação das águas nesse município foi interrompida, pois muitas amostras de água apresentaram níveis de flúor abaixo dos valores mínimos aceitáveis.

Abstract Introduction Fluoridation of public water supply is an important measure in the prevention of dental caries. Objective This study aimed to monitor the fluoride (F) concentrations of a public water supply with water fluoridation program in a small municipality in the Northeast region of Brazil. Material and method It is a quantitative study with a descriptive approach. Three points of the urban area were selected for collecting water samples twice a month for 12 months. The average of F concentrations was calculated considering these three samples of each collection point at the same occasion. F concentrations in the water samples were determined by potentiometry and the results were classified according to the criterion proposed by criterion set down by Collaborating Center of the Brazilian Ministry of Health for Oral Health Surveillance. The samples were classified according to the best risk-benefit adjustment (0.55 – 0.84 mg F /L). Result Less than 10% of the samples were within the ideal range. Conclusion It was observed that water fluoridation in this municipality was interrupted since many water samples showed f-levels below the minimal acceptable values.