Abstract
An entropy-weighted water quality index (EWQI) was used in this study to evaluate the quality of groundwater in parts of the Ibadan metropolis, Nigeria. 75 groundwater samples were collected and analysed for pH, electrical conductivity, total hardness, alkalinity, turbidity, total dissolved solids, cations (Na+, K+, Ca2+, Mg2+), anions (HCO3−, Cl−, SO42−, NO3−, F−), Fe and Total Heterotrophic Bacteria Content (THBC). The pH of the groundwater in the study area ranges from slightly alkaline to neutral. Based on the average concentrations, the abundance of anions is in the order as follows: Cl−> HCO3−> SO42−> NO3−> F− while that of cations is Na+> K+ > Ca2+ > Mg2+. The groundwater was predominantly mixed and Na-Cl hydrogeochemical facies types and was thought to be controlled by multiple processes including water-rock interaction and mineral weathering. The prevalent bacteria in this study are Klebsiella pneumonia, Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. The average EWQI value was 32.8, with values ranging from 2.2 to 143.6. Most of the groundwater in the research area, according to the EWQI, is good to excellent quality for drinking, while only 20% of the samples were medium to low quality, necessitating minimum treatment.