Hydrogeochemical Assessment of Groundwater in Epe (Nigeria) for Drinking and Irrigation Purposes

Groundwater sustainability demands routine quality monitoring. This study assessed the hydrogeochemistry of groundwater in Epe, Lagos State, to evaluate its suitability for drinking and irrigation. Fifty well-water samples from eight communities were analyzed for pH and major ions. Results showed that parameters complied with regulatory standards in most locations except magnesium (65.70±23.50 - 96.00±19.68 mg/L) which consistently exceeded the Nigerian Standard for Drinking Water Quality of 20 mg/L. Dietary intake of essential elements was generally negligible, though magnesium levels in Poka exceeded recommended daily allowance for infants (0-6 months). The Water Quality Index (40.41 - 128.49) classified the water as 8% “excellent,” 76% "good," and 16% "poor" while the Pollution Index of Groundwater (0.39 - 0.85) ranked all samples as having insignificant pollution. Though, majority of the irrigation indices indicated suitability for irrigation; Permeability Index (<25% in 88% of samples), Magnesium Adsorption Ratio (>50% in 86% samples) and Corrosivity Ratio (>1 in 50% samples) presented risks to long-term soil permeability and metallic water transport pipes. The ionic dominance was Mg²⁺>Ca²⁺>Na⁺>K⁺ and HCO₃⁻>SO₄²⁻>Cl⁻. Geochemical diagrams (Piper, Chadha and Schoeller diagrams) revealed a Ca-Mg-HCO₃ facies, attributed to mixed carbonate-silicate weathering (Gaillardet diagram), rock-water interaction (Gibb’s diagram) and ion exchange (CAI, CAII), with the Hydrochemical Facies Evolution Diagram indicating mixed facies. Principal Component Analysis identified bicarbonate (PC1: 57.33%), calcium (PC2: 17.35%), sulphate (PC3: 15.94%) and magnesium (PC4: 8.38%) as the primary factors controlling water quality. The study recommends water treatment, the use of corrosion-resistant pipes, and sustained monitoring to safeguard this resource.