Bacteriological Evaluation of Groundwater Quality and Risk Factors for Contamination in Semi-Arid Communities of Yobe State

Groundwater is the primary water source for communities across Yobe State, North East Nigeria, yet systematic bacteriological evaluation of its quality in semi-arid settings characterised by seasonal water table fluctuation is lacking. This study conducts a comprehensive bacteriological evaluation of groundwater quality and identifies contamination risk factors in five LGAs in Yobe State. Groundwater samples from 80 boreholes and hand-dug wells were collected in dry and rainy seasons and analysed for total coliform, faecal coliform, Escherichia coli, and heterotrophic plate count using membrane filtration and pour plate methods. A structured risk factor survey covered well construction standards, latrine proximity, surface drainage patterns, and livestock management around water sources. Faecal coliform was detected in 47 percent of hand-dug wells and 19 percent of boreholes. Contamination was significantly higher during the rainy season. Latrine proximity within 15 metres (OR 4.2) and unlined well walls (OR 3.8) were the strongest contamination risk predictors. Salmonella and Vibrio cholerae were isolated from five samples each. Regression modelling identified well type, casing depth, and seasonal flooding frequency as jointly predictive of bacteriological quality. The study provides actionable risk factor data for Yobe State Rural Water Supply and Sanitation Agency to prioritise borehole rehabilitation and sanitation separation interventions in the highest-risk communities. Keywords: groundwater quality, Yobe State, faecal coliform, risk factors, semi-arid