Abstract
<jats:p>Groundwater is one of the main sources of drinking water in Uruguay and has traditionally been suitable for human consumption. However, increasing agricultural and industrial demand, coupled with a lack of updated hydrochemical data, has raised concerns about fluoride (F⁻) and arsenic (As) contamination. In this study, hydrochemical data from 1,761 groundwater samples collected by the General Directorate of State Sanitary Services (OSE, personal communication, September 2025) and private sources across Uruguay (except Maldonado and Montevideo departments) were analysed. Arsenic concentrations ranged from 0.001 to 0.046 mg/L, with 5% of the samples exceeding the World Health Organization (WHO) recommended limit of 0.01 mg/L. Fluoride concentrations ranged from 0.04 to 2.5 mg/L, with 12% of samples exceeding the WHO limit of 1.5 mg/L. The highest fluoride concentrations were observed in the departments of Cerro Largo and Treinta y Tres, while arsenic anomalies were associated with sedimentary formations such as the Raigón and Mercedes formations. Selenium (Se) concentrations ranged from 0.1 mg/L to 0.5 mg/L. Multivariate statistical techniques, including Principal Component Analysis (PCA) and cluster analysis, revealed distinctive hydrochemical patterns. Furthermore, a Groundwater Quality Index (GrWQI) was developed, integrating pH, EC, F⁻, As, and Se, with weighted contributions based on health risk. GrWQI values showed spatial heterogeneity, with several areas in the departments of Salto, Soriano, and Rocha presenting lower scores, indicating potential health risks. These findings highlight the urgent need for continued groundwater monitoring and management strategies.</jats:p>