Which statement about air-gap separation distance is true?

• A. It must be at least 1 inch or twice the diameter of the supply pipe, whichever is greater
• B. It must be exactly 1 inch
• C. It must be at least twice the diameter of the supply pipe, regardless of diameter
• D. It is not required for most systems

Answer: (A)

Air-gap separation distance is the physical gap that must exist between the outlet of a potable-water supply and the receiving surface to prevent backflow. The true rule here is that this gap must be at least 1 inch, but if the supply pipe diameter is larger, the gap must be at least twice the diameter of that pipe, whichever amount is greater. This sizing protects against backflow by ensuring a sufficient buffer that scales with pipe size, so bigger pipes don’t have an inadequately small gap that could allow backflow under pressure or siphon conditions. It’s not a one-size-fits-all 1-inch rule, and it’s not something that’s generally unnecessary in most systems.