Massachusetts Plumbers Journeyman Practice Exam 2026 - Free Plumber Journeyman Practice Questions and Study Guide

The correct answer indicates that the minimum required air gap should be twice the effective opening of a potable water outlet. An air gap is a critical component in plumbing systems designed to prevent backflow contamination into the potable water supply. By ensuring that the air gap is at least twice the diameter of the outlet, it minimizes the risk of any potential cross-contamination.

This standard is established to provide enough vertical separation between the highest possible water level in a fixture and any possible back-siphoning that might occur, thus ensuring safe and clean drinking water. When considering the safe operation of plumbing systems, this requirement helps maintain public health standards by preventing contaminants from re-entering the clean water supply.