Which system size is required to comply with disinfection profiling by January 2003?

The requirement for disinfection profiling pertains primarily to the size of the water systems and their corresponding populations served. Systems that serve between 500 and 9,999 people are mandated to comply with disinfection profiling, which became fully effective by January 2003. This regulation was established to ensure adequate disinfection practices in medium-sized water systems to protect public health from waterborne pathogens. These systems are larger than small, non-community or transient systems, which may not have the same level of public health exposure risk due to their limited service population.

Smaller systems, such as those serving less than 100 people or between 25 to 499 people, generally face different regulations and thresholds regarding disinfection profiling. Likewise, transient, noncommunity systems, which serve people for a short period and do not have a permanent resident base, also fall outside the scope of this specific requirement. Thus, the focus on systems serving 500 to 9,999 people in terms of compliance reflects regulatory intentions to prioritize community water systems that have a greater number of consumers who may be consistently exposed to the water supply.