Master Plumber Practice Exam 2026 - Free Plumber Practice Questions and Study Guide

The air gap is a plumbing fixture specifically designed to prevent backflow, which is the undesirable reversal of the flow of water or other substances into the potable water supply. It works by creating a physical separation between the end of a potable water supply outlet and the highest point of the downstream water line, ensuring that contaminants cannot siphon back into the clean water system. This is critical for maintaining safe drinking water standards, particularly in situations where non-potable water or waste materials could otherwise enter the water supply.

Air gaps are commonly found in the installation of dishwashers and sinks where the potential for backflow exists, making them a key component of plumbing systems aimed at preventing contamination. Other plumbing fixtures mentioned—such as water heaters, dishwashers, and sump pumps—do not inherently include features for backflow prevention in the same manner that an air gap does. While some of these fixtures may be installed with additional backflow prevention mechanisms, they do not provide the same straightforward physical separation that air gaps do.