What is considered the most effective method of cross-connection control?

A physical air gap is the most effective method of cross-connection control because it creates a clear and substantial separation between the potable water supply and any potential contaminants. An air gap prevents backflow by ensuring that water cannot enter the drinking supply through siphoning or other means, as there is a physical space that must be crossed.

This method is particularly effective because it does not rely on mechanical parts, which can fail over time. Even in cases of pressure fluctuations or unexpected changes in the system, the air gap remains a reliable barrier against contamination.

In contrast, while other methods like check valves, pressure regulation, and vacuum break devices provide important safeguards, they may not be as foolproof as an air gap. For instance, check valves can malfunction or become stuck, allowing backflow under certain conditions. Similarly, vacuum breakers can fail if not installed or maintained properly, and pressure regulation devices are designed to control flow rates rather than directly prevent backflow. Thus, the physical air gap stands out as the most straightforward and reliable defense in preventing cross-connections and protecting drinking water quality.