Rhode Island Journeyman Plumber Practice Exam 2025 - Free Journeyman Plumber Practice Questions and Study Guide

The air gap is the correct answer because it serves as a crucial device that ensures the safety of the water supply by preventing backflow into the potable water system. Specifically, in the context of a dishwasher, the air gap provides a physical space between the end of the dishwasher’s drain hose and the flood level of the sink or drain, effectively creating a barrier. This design prevents contaminated water from siphoning back into the fresh water supply, which can occur during washing cycles.

With an air gap installed, any overflow or backflow that might occur in the dishwasher will spill out into the sink rather than reverse into the water supply lines, thereby protecting the drinking water from potential contamination. This is particularly important in plumbing systems where dishwashers are used, as they may handle dirty water that could contain food particles, grease, and other contaminants.

In contrast, while the other options also relate to plumbing and safety, they do not specifically function to protect against the contamination of water entering a dishwasher in the same direct manner that an air gap does.