The karst landscape of Trenggalek Regency, located in several sub-districts including Dongko, Kampak, and Watulimo, is shaped by the Wonosari Formation and is characterized by springs and underground rivers. Due to water scarcity in the region, local communities heavily depend on these natural water sources. This study assesses the groundwater quality of 16 springs and 20 underground rivers to evaluate their suitability for consumption and associated health risks. Using the groundwater quality index (GWQI), human health risk assessment (HHRA), and statistical methods, various physicochemical parameters were analyzed, including pH, total dissolved solids (TDS), electrical conductivity (EC), and concentrations of iron (Fe²⁺), manganese (Mn²⁺), calcium carbonate (CaCO₃), and sulfate (SO₄). Water generally meets the World Health Organization standards for safe drinking. However, correlation analysis reveals notable mineral dissolution and possible anthropogenic influence. TDS strongly correlates with EC (r = 0.97), while Fe²⁺ shows significant relationships with Mn and TDS. Conversely, CaCO₃ shows a negative correlation with EC and TDS, suggesting alternative sources beyond rock weathering. The HHRA indicates higher non-carcinogenic health risks from Fe²⁺ contamination in underground rivers compared to springs. The study’s novelty comes in its integrated assessment of groundwater quality and health hazards in Trenggalek’s karst region, which uses GWQI, HHRA, and statistical analysis to show geochemical interactions and highlight iron-related health issues in underground rivers.