Which of the following is NOT a category of drinking water systems covered by O.Reg 170/03?

The correct answer is commercial systems because O. Reg. 170/03 primarily regulates drinking water systems based on their classification as municipal water systems. The regulation stipulates standards and requirements for two main categories: small municipal systems and large municipal systems, which pertain to local government-operated water supplies serving communities.

Small municipal systems are defined as those serving a lesser number of connections or residents, whereas large municipal systems cater to larger populations, thereby requiring more stringent oversight due to their capacity and the potential impact on public health. Non municipal year-round residency systems are also included under this regulation, as they have specific requirements aimed at ensuring safe drinking water for residents outside traditional municipal structures.

Commercial systems, on the other hand, often include private or business-operated sources of drinking water, which may not fall under the same regulatory framework as municipal water systems. This distinction is crucial for understanding the scope of water quality regulations in Ontario, thereby indicating why commercial systems do not fall within the purview of O. Reg. 170/03.