Which of the following is an advantage of using an air gap?

An air gap is a physical separation between the water supply and a potential contamination source, making it an effective method for preventing backflow. The primary advantage highlighted in this context is that only a visual check is needed to verify whether the air gap is functioning properly. This simplicity is beneficial for maintenance and regulatory compliance. If the air gap is intact and properly designed, it is usually easy for operators to see that there is a sufficient space between the water outlet and the contaminated source, thus ensuring that backflow is effectively prevented without requiring complex testing or monitoring equipment. This ease of oversight contributes to its favorability as a backflow prevention method in various applications.

Other options, such as requiring complex monitoring or mandating a continuous water supply, detract from the practicality and effectiveness of the air gap as a simple and reliable solution to backflow issues. The economic aspect is also less relevant compared to the straightforward functionality of a visual inspection.