What is the purpose of an air gap in plumbing systems?

The purpose of an air gap in plumbing systems is to prevent backflow of contaminants. An air gap is a physical separation between the end of a water supply outlet and the flood level of a receptacle to which the outlet is connected. This separation creates a barrier that effectively prevents contaminated water from flowing back into the clean water supply due to backpressure or siphoning effects.

By maintaining this gap, any potential for backflow—that might occur due to changes in pressure within the plumbing system—is eliminated, thereby safeguarding the potable water supply from pollutants. This practice is critical for ensuring public health and safety, especially in settings where there is a risk of cross-contamination from appliances like dishwashers or sinks.

Other options touch on aspects of plumbing systems, such as water pressure management, thermal expansion, and drainage improvements, but they do not align with the fundamental purpose of an air gap, which is specifically to prevent the introduction of contaminants into the drinking water supply.