The study on the growth of chlorine resistant bacteria in water supply systems is critical for the assessment, control, and prevention of microbiological safety associated with drinking water. In this study, bulk water and biofioms in water supply system sourced from lakes and reservoirs in cold region were investigated by the detection of heterotrophic bacteria and chlorine resistant bacteria, and the biota in the biofilm were observed by scanning electron microscope. Results showed that the bacteria regrowth still existed in the bulk water even within more than 0.20 mg/L free chlorine in the distribution systems. Chlorine-resistant bacteria survived pervasively in the studied water supply system. The chlorine-resistant bacteria in post-chlorination and distributed water were less than 350 CFU/mL. The number of chlorine-resistant bacteria in the biofilm was two orders of magnitude higher than that of the bulk water in general. The chlorine resistant bacteria presented most in pre-chlorination of sand filter water and biofilm, while almost all viable bacteria in the clearwell were chlorine-resistant bacteria. Microbial morphologies in the biofilms of water supply systems were composed of cocci and rod, with the latter especially predominated in the biofilms.