CSLB Class B General Contractor's License Practice Exam

A backflow prevention device is essential in plumbing systems to prevent the reverse flow of water, which can lead to contamination of the potable water supply. An air gap is a specific type of backflow prevention mechanism that ensures there is a vertical distance between the water outlet and the water level in the receiving vessel. This gap effectively breaks the flow path, preventing any possible backflow that could occur if pressure changes in the system.

The other options listed are not backflow prevention devices. A water closet is simply a fixture used for sanitation purposes and does not serve a role in preventing backflow. Similarly, a sewer pipe is a conduit for wastewater, and while it is part of the plumbing infrastructure, it does not prevent backflow; in fact, if not properly managed, sewer lines can contribute to backflow issues. Thus, the air gap stands out as the sole correct choice when identifying devices specifically designed for backflow prevention.