EVALUATING MICROBIAL AND PHYSICOCHEMICAL CONTAMINATION OF GROUNDWATER IN SOUTHWESTERN NIGERIA AND THE FEDERAL CAPITAL TERRITORY: A REGULATORY COMPLIANCE ASSESSMENT

Abstract

Microbial contamination renders groundwater unsafe and scarce. This study assessed groundwater quality across Lagos, Ogun, Oyo, Osun, Ondo, Ekiti States, and the Federal Capital Territory to evaluate compliance with water quality guidelines of the World Health Organization (WHO), Standard Organization of Nigeria (SON), and the National Environmental Standards and Regulations Enforcement Agency (NESREA). A total of 450 samples from 49 towns were analyzed for physical (temperature, electrical conductivity), chemical (magnesium, calcium, total hardness), and microbiological (bacterial load, faecal coliforms, pathogenic bacteria, protozoans) parameters using standard methods. Results revealed widespread contamination with total hardness (258.11±58.33 - 572.06±63.82 mg/L) and bacterial load (1.67±4.08 t- 37,241.00±113,412.90 cfu/mL) exceeding regulatory limits. Faecal coliforms were found in 30.22% of samples. Among 11 bacterial species isolated, Enterobacter aerogenes (52.7%), Klebsiella pneumoniae (31.8%), and Escherichia coli (30.7%) predominated. Entamoeba histolytica, a pathogenic protozoan was found in 15% of samples. Water Quality Index classified 9.33% of sources as “excellent,” 15.56% “good,” 9.33% “poor,” 2.89% “very poor,” and 62.89% “unsuitable” for use without treatment. Principal Component Analysis identified bacterial load as the key parameter (Loading: 1.00; PC1: 99.98% variance) influencing water quality. It was recommended that improved sanitation infrastructure, regulatory monitoring and treatment be implemented to safeguard public health.