Waterborne disease outbreaks are especially dangerous in immunocompromised individuals and can be caused by biofilm formation in water systems. The aim of this work was to collect a group of environmental isolates, including opportunistic pathogens, from treated water systems with the purpose of creating a model drinking water system biofilm. This model biofilm would be used to explore the resistance of biofilms to chlorine at levels typical of a water distribution system. Isolates for the model biofilm were collected from Calgary and Ontario, sequenced and then as single and multi-species biofilms exposed to chlorine. The resistance, biofilm structure and microbial community were examined. It was found that biofilm organisms are consistently more resistant than planktonic and that multi-species biofilms even more so. Little change was seen in biofilm communities after treatment. The 3D structure of the biofilm appeared to have a role in resistance by limiting diffusion and protecting inner cells.