A potable water connection to a boiler feed water system shall be made through an ________ to prevent backflow.

A potable water connection to a boiler feed water system should indeed be made through an air gap to prevent backflow. An air gap is a physical separation between the end of a supply line and the available flood level of a fixture or receptacle. This space ensures that there is no direct connection that could allow the contaminated water from the boiler system to siphon back into the potable water supply, which could lead to contamination of the drinking water.

Air gaps are an effective design feature because they are simple and rely on gravity rather than mechanical parts, thus reducing the risk of failure over time. This is crucial in plumbing systems where the integrity of the potable water supply must be maintained.

While backflow preventers also serve a similar purpose by blocking reverse flow, air gaps are often considered the most effective method for protecting potable water against contamination in these scenarios. Other options, such as pressure relief valves and expansion tanks, serve different functions in a plumbing or heating system and do not specifically address the prevention of backflow from a boiler feed water system to a potable water supply.