This research illustrates microbial instability of water from point of heterotrophic bacteria (HPC) amplification in accordance with residual chlorine, pH, temperature, dissolved oxygen (DO) and alkalinity (Alk) in hospital water.  Hundred-fifty samples were collected from hot and cold tap water systems. Residual chlorine, pH and temperature were determined promptly in place; HPC was cultured on R2A culture media and spread plate method. DOand Alk was determined by Winkler and photometric methods, respectively. HPC was detected in 96% of samples therefor fifty-two percent had higher than the recommended standards and HPC density in samples been 947±998 CFU/ml. The highest contamination was detected in cooling systems, gynecological, NICU and sonography ward (1500-2000 CFU/ml) and the lowest was inendoscopy, laboratory and drug store (125-175 CFU/ml). Spearman correlation and multivariate linear regression revealed that HPC density in cold water has negative correlation with Cl2, temperature and DO and positive correlation with pH and Alk. In warm water HPC density has negative correlation with temperature, pH, and DO and positive correlation with Cl2 and Alk. Chi2 test revealed that higher densities (>500 CFU/ml) in cold water was more frequently than warm water (OR: 2.3). HPC has unexpected distribution in water. Occurrence of high densities of HPC can be affect the presence of hazardous bacteria so, it is advised to implement the routine test of HPC monitoring with indicator bacteria and remark the effective efforts for hospitals’ water disinfection for assurance of water safety.