What defines a cross-connection in plumbing?

A cross-connection in plumbing is defined as a connection between potable (safe drinking) water and non-potable water (which may be contaminated or unsafe). This definition is critical for ensuring the protection of drinking water supplies; even minor connections can inadvertently allow non-potable water to flow into potable lines, risking contamination. The primary concern with cross-connections is the potential for backflow, where non-potable water is drawn back into the clean water supply. This is why plumbing codes and regulations place significant emphasis on identifying, preventing, and properly maintaining such connections to protect public health and safety.