Access to microbiologically safe drinking water remains a major public health challenge in rural and peri-urban communities of northern Nigeria, where reliance on shallow boreholes exposes residents to both physicochemical and microbial contamination. This study assessed the physicochemical characteristics of borehole water and evaluated the bactericidal efficacy of a combined Moringa oleifera seed powder and aluminium sulphate (alum) coagulant, applied in a 50:50 ratio at three dosages (10 g, 20 g and 30 g), against Escherichia coli and total coliform bacteria in borehole water sampled from eleven wards of Mubi North Local Government Area, Adamawa State, Nigeria. Water samples were analysed for pH, turbidity, total dissolved solids (TDS) and colour, and results were compared against the Nigerian Standard for Drinking Water Quality (NSDWQ) and World Health Organization (WHO) guideline values. Baseline E. coli counts ranged from 2.60 × 10² to 3.00 × 10⁴ CFU/100 mL and total coliform counts from 27.7 to 158.0 CFU/100 mL, both well above their respective regulatory limits (0 CFU/100 mL for E. coli; 10 CFU/100 mL for total coliform). Treatment with the combined coagulant produced a clear dose-dependent reduction in bacterial load: E. coli was reduced to the compliant 0 CFU/100 mL level in all eleven wards only at the highest dose (30 g), while total coliform reached 0 CFU/100 mL in four wards (Bahuli, Betso, Digil, Kolere) at 30 g but plateaued at exactly the 10 CFU/100 mL limit in the remaining seven wards, indicating incomplete disinfection of this bacterial group even at the highest dose tested. Physicochemical results showed pH (6.3–7.1) largely within the acceptable range and turbidity (3.0–5.5 NTU) within the 5 NTU guideline value in all wards except Lokuwa (5.5 NTU), while TDS (92–281 mg/L) was well within the 500 mg/L limit at every location. These findings indicate that the Moringa oleifera–alum combination is a low-cost, locally sourced and effective bactericidal treatment for microbially contaminated borehole water, particularly against E. coli, although total coliform removal was less complete and would benefit from further optimisation.