Where is an air gap required in cold water installations, and why?

• A. At points where a fixture drains to a non-potable source (e.g., dishwasher, washing machine, or at a sink for drain connections) to prevent siphonage back into the supply.
• B. On the hot water supply line.
• C. Inside the main water meter.
• D. On the irrigation line.

Answer: (A)

Air gaps prevent backflow by creating an unobstructed vertical space between the potable water outlet and the non-potable drain, so contaminated water cannot be siphoned back into the supply. In cold-water installations, they’re required where a fixture or appliance drains to a non-potable source—like a dishwasher or washing machine—and even at a sink drain connection that could siphon back into the supply. This simple, reliable separation works even if a valve fails, because water must pass through the air gap before entering the drain, stopping any backflow into the potable system. It’s not placed on hot-water lines, and it’s not located inside the main meter; irrigation systems use other backflow protections rather than a standard air gap in this context.