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

The purpose of an air gap in plumbing fixtures is to prevent backflow. An air gap is a physical separation between the end of a water supply outlet and the flood level rim of a fixture, such as a sink or bathtub. This design is crucial in safeguarding potable water systems from contamination. When water flowing through a supply line drops in pressure, there is a risk that contaminated water from the drain system could backflow into the clean water supply. The air gap effectively eliminates this risk by creating a space through which contaminated water cannot travel back into the system, thus maintaining the safety and purity of drinking water.

In contrast, options that suggest enhancing pressure, filtering water, or collecting rainwater do not align with the fundamental role of an air gap. Enhancing pressure typically involves different mechanisms and devices within plumbing systems, while filtering water relates to processes designed to remove impurities, such as using physical or chemical filtration systems. Collecting rainwater involves specific systems designed to capture and store precipitation, which is unrelated to the function of an air gap in preventing backflow.