What is the minimum air gap allowed between the lowest end of a water supply outlet and the fixture's flood rim?

The minimum air gap required between the lowest end of a water supply outlet and the fixture's flood rim is crucial for preventing backflow, which could lead to contamination of the drinking water supply. An air gap serves as a physical barrier that allows for drainage without the risk of siphoning any contaminated water back into the clean water supply.

In residential plumbing, the established minimum distance is 1 inch. This standard is widely accepted in plumbing codes and regulations to ensure safety and proper function. A 1-inch air gap creates a sufficient separation that helps prevent potential backflow incidents in typical scenarios. This measurement, however, may vary depending on specific conditions or local regulations, but in general practice and according to codes, it is recognized as the safe minimum distance.

The other options represent greater distances that exceed the minimum requirement, providing additional safety margins which, while beneficial in some situations, are not necessary under standard conditions where a 1-inch air gap adequately suffices.