There are growing numbers of cross-contamination threats that could contaminate drinking water .Microbiological contaminants can enter drinking water system through flush toilet system installed inside. Four samples were collected from five floors building to represent the contamination of drinking water .To confirm the results five repitation of the samples were conducted .A total number of samples collected were 96 .The MPN/100 ml.of water sample were detected for fecal coliforms. The results suggested that tap water could be a potential transmission route for many diseases and may pose a health hazard.