Isolation and identification of coliforms from public water supplies in Lagos state, Nigeria

Access to safe drinking water is essential for public health, yet contamination of water sources remains a significant concern, particularly in developing regions. This study aimed to assess the bacteriological quality of water from four major water treatment plants in Lagos State—Adiyan, Iju, Ijanikin, and Ikeja—by isolating and identifying coliform bacteria in both raw and treated water samples. Water samples were collected in sterile glass bottles and analyzed for pH, residual chlorine, total bacterial count, and coliform presence using the Most Probable Number (MPN) method, Gram staining, and biochemical tests, including the Analytical Profile Index (API). The results revealed no residual chlorine (0.0 mg/L) in all treated water samples, indicating a lack of continuous disinfection. pH values ranged from 6.7 to 7.1, falling within WHO standards (6.5–8.5). Total bacterial counts (TBC) in raw water were highest in Iju (27 CFU/mL) and lowest in Ikeja (16 CFU/mL), while treated water showed reductions, with Iju at 11 CFU/mL and Ikeja at 3 CFU/mL. Coliform counts in raw water ranged from 8 to 14 MPN/100mL, while treated water ranged from 4 to 11 MPN/100mL, exceeding the WHO limit of zero coliforms per 100mL. Klebsiella pneumoniae, Escherichia coli, and Pantoea spp. were identified in both raw and treated samples, with E. coli detected in Ikeja raw water, confirming fecal contamination. The persistence of coliforms in treated water suggests treatment inefficiencies, pipeline contamination, or bacterial regrowth within the distribution system. These findings underscore the urgent need for improved chlorine dosing, pipeline maintenance, routine microbial monitoring, and alternative disinfection methods to ensure the microbiological safety of Lagos public water supplies.