What is the minimum air gap required for a typical residential faucet?

The minimum air gap required for a typical residential faucet is best represented by the guideline of being at least twice the diameter of the supply pipe. This standard is established to ensure proper backflow prevention, as the air gap acts as a physical separation between the water supply and any contaminated source, preventing the risk of back siphonage. By requiring that the air gap be double the pipe's diameter, it provides a significant buffer against potential contamination, accommodating a range of conditions that might affect water flow.

In other words, this standard ensures that the distance from the outlet of the faucet to the highest potential water level or the flood rim of a receiving fixture is sufficient to prevent any backflow situation. This is crucial in a residential setting, where connections exist between potable water systems and various fixtures that can pose a contamination risk.

While other options suggest fixed measurements, relying on a ratio based on pipe diameter allows for flexibility depending on the system's design, making it a widely accepted practice in plumbing code.