The study of the effect of water guard on microorganisms isolated from domestic water collected and stored for use in various homes in Makurdi metropolis was carried out. A total of 80 samples of water were randomly collected from locations in Makurdi which include; high-level, North bank, Wurukum and Wadata and analyzed for bacteria contamination. Microorganisms isolated from the water before treatment include: Escherichia coli (31.92%), Klebsiella spp (11.39%), Diphtheroid spp (13.94%), Staphylococcus aureus (17.89%), Salmonella typhi (9.42%), Enterobacter aerogenes (8.00%) and Streptococcus faecalis (7.44%). The microorganisms isolated after treatment of water with water guard include: Escherichia coli (49.27%), Klebsiella spp (16.79%), Diphtheroid spp (6.57%), Staphylococcus aureus (27.37%). The most prevalent organism in water after treatment was Escherichia coli due to its presence in almost all the locations after treatment. The result shows significant differences in the occurrence of microorganisms present in untreated and treated water samples at p<0.05. Some of the bacteria isolated before treatment of water with water guard were not seen after treatment. Monitoring of the effect of exposure time of the microbes to water guard is advocated.