Seasonal hydrogeochemical and microbial assessment of drinking water in basement complex rocky-hill communities of Southwestern Nigeria: environmental, public health and water security implications

Access to safe drinking water remains a major environmental and public health challenge in basement complex terrains of sub-Saharan Africa, were hydrogeological conditions and seasonal variability influence groundwater quality. This study evaluated the physicochemical and microbiological quality of borehole water, hand-dug wells, and harvested rainwater in three rocky-hill communities (Ilawe-Ekiti, Aramoko-Ekiti, and Iyin-Ekiti) in Southwestern Nigeria. Seventy-two water samples collected during the dry (January–February 2026) and wet (March–April 2026) seasons were analyzed using standard APHA methods. Parameters assessed included pH, electrical conductivity, total dissolved solids, turbidity, hardness, nitrate, total coliforms, and Escherichia coli. Two-way ANOVA, principal component analysis (PCA), Water Quality Index (WQI), WHO guideline comparison, and nitrate health risk assessment were applied. Physicochemical parameters generally complied with WHO limits, although well water exhibited higher ionic content due to water–rock interactions. Microbial contamination was the major water quality concern, with hand-dug wells recording the highest total coliform and E. coli counts during the wet season. PCA explained 72.8% of total variance, distinguishing anthropogenic contamination from geogenic processes. Most samples were classified as good to excellent by WQI, while nitrate risk remained low to moderate. The findings emphasize integrated groundwater protection, sanitation, and community-level water treatment to enhance drinking water safety.