In plumbing, what does the term "air gap" refer to?

The term "air gap" in plumbing refers to a safety feature designed to prevent backflow, which is the undesirable reversal of flow of water or other substances. An air gap is essentially a physical separation between the end of a water supply outlet and the highest point of a downstream sanitary drainage system. This gap allows air to break the connection between the two systems, ensuring that contaminated water cannot siphon back into the clean water supply.

By maintaining this physical separation, the air gap serves as a critical barrier that protects the potable water supply from contamination due to backflow events, especially in situations where there might be a drop in water pressure. This is particularly relevant in scenarios where plumbing fixtures are connected to devices that might introduce contaminants, like dishwashers or sink drains.

In contrast, the other options relate to different aspects of plumbing. For instance, methods of providing pressure, types of pipe connections, and measures of volume do not specifically address the critical function of an air gap, which is purely focused on backflow prevention.