How is a cross-connection defined?

A cross-connection is defined as a situation where a potable (drinking) water supply is connected to another water supply that may not be safe or suitable for drinking. This connection can lead to the potential for contaminants from the non-potable water supply to flow back into the potable system, creating a significant health hazard due to the possibility of backflow.

In this context, the correct choice highlights the critical concern of ensuring that drinking water remains uncontaminated by other sources. The definition emphasizes the importance of maintaining the integrity of the potable water system to safeguard public health. By identifying a potable supply connected to another water source, this option accurately describes the risk associated with cross-connections, which must be controlled and monitored in drinking water systems to protect consumers.