Andrea Machado, Antonio Samudio , Héctor D. Nakayama, Gustavo Brozón B. , Víctor González, Claudia Avalos, Carlos Méndez, Andreas Ries, Heriberto Núñez , Carlos Enciso

Groundwater is the largest freshwater reserve on the planet, and its quality plays a fundamental role in human well-being and economic development. However, it sometimes contains potentially harmful compounds, such as fluoride in high concentrations, which has led to the implementation of quality standards to ensure water potability. This study evaluates the concentrations of fluoride in groundwater from the state of Paraguarí, Paraguay, and studies the joint occurrence of fluoride with elements such as calcium, magnesium, sodium, and potassium. Forty-one water samples were collected from boreholes at different locations in the state of Paraguarí. The results showed that 7% of the samples exceeded the maximum concentration limit allowed by the Paraguayan Standard and the World Health Organization, this means concentrations were above 2 mg/L; this was observed mainly in the district of Caapucú. These findings indicate that 93% of the wells meet potability standards. Additionally, fluoride was found to correlate with the sodium content in groundwater. The results suggest the need for continuous monitoring and implementation of effective fluoride reduction technologies, especially in areas with elevated concentrations.