Hydrochemistry and environmental isotope signatures (δ18O and δ2H) in the crystalline basement groundwater system of Oye-Ekiti, southwestern Nigeria

= 0.87], indicating that the groundwater is predominantly of meteoric origin and derived from recent precipitation. The d-excess values (8.7-12.2‰), clustering around the global average of 10‰, suggest limited evaporative influence prior to recharge. Slight isotopic enrichment and higher solute variability in shallow hand-dug wells highlight their greater vulnerability to surface processes. These findings provide a new geochemical and isotopic baseline, providing critical insights for sustainable groundwater management, monitoring, and policy implementation under Sustainable Development Goals (SDG) 6 in a rapidly urbanizing environment.