Water quality, in either a well or a distribution system, is affected by many factors. Biofilms often are the result of interactions between existing piping systems which have some deposits or growth, and which experience some form of contamination through disinfection breakdown or through the entrance of organisms into the system. It is not always necessary for the pipe to have been in use for a long period of time. Installation and maintenance practices also can impact water quality, even in new pipe.
The presence of biofilms in public drinking water systems is a topic that has been widely discussed and studied in the last decade. While biofilms themselves may not constitute a serious health risk, when they're combined with inadequate or absent disinfectant residuals, they set the stage for opportunistic bacteria to develop into a true health hazard.