Groundwater quality and public health risks in a semi-urban Nigerian community: Bacteriological and organoleptic evidence from Isara-Remo

Abstract

Groundwater is the primary source of domestic water supply in many semi-urban communities in southwestern Nigeria, yet its quality is increasingly threatened by microbial contamination arising from inadequate on-site sanitation. Physicochemical, organoleptic and bacteriological analyses were conducted on twelve (12) hand-dug wells (W1 – W12) in Isara-Remo, Ogun State, during the wet season (June – August 2024). Well depth, construction characteristics and distance to the nearest pit latrine were documented, and laboratory analyses were performed using standard methods (APHA, 2017). Results were evaluated against World Health Organization (WHO, 2022) and Standards Organisation of Nigeria (SON, 2015) drinking-water guidelines, and Pearson correlation analysis was used to examine relationships between microbial indicators and environmental variables. The wells were shallow (mean depth = 14.2 ± 1.7 m) and located at a mean distance of 15.5 ± 7.5 m from pit latrines, below the WHO-recommended minimum of 30 m. Offensive odour and sour taste were observed in six wells. Turbidity (1.5 – 14.2 NTU), nitrate (7.2 – 66.8 mg/L) and iron (0.03 – 0.91 mg/L) exceeded guideline limits in several samples. Total heterotrophic bacteria, total coliforms and Staphylococcus aureus were detected in all wells, indicating widespread faecal contamination. Microbial indicators showed strong positive intercorrelations and significant inverse relationships with distance to pit latrines. Although most physicochemical parameters complied with drinking-water standards, the pervasive presence of microbial indicators renders groundwater in Isara-Remo unsafe for direct consumption, underscoring the need for improved sanitary separation.