What is a physical link between a potable water system and one of unknown quality?

A physical link between a potable water system and one of unknown quality is referred to as a cross connection. This term denotes a potential connection point where water could flow from a non-potable source into a drinking water supply. Such connections create a significant hazard for contamination, as pollutants or contaminants from the source of unknown quality can be drawn into the potable water system, especially under conditions of backflow due to pressure changes.

Understanding the context, backflow prevention devices are essential to mitigate this risk, but they are not the link itself; they provide protection against the effects of a cross connection. Pressure relief valves and isolation valves serve specific functions in water systems, including maintaining pressure and isolating sections of the system for repair or maintenance, but they do not create a direct physical link between potable and non-potable water sources. Thus, the concept of a cross connection is crucial for understanding the health and safety implications of water system management.