What is the purpose of an air gap in plumbing?

The purpose of an air gap in plumbing is to prevent backflow, which is the unwanted reverse flow of water in a plumbing system. An air gap is a physical separation between the end of a water supply outlet, such as a faucet, and the flood level rim of a fixture, such as a sink or bathtub. This mechanism is essential in protecting potable water from contamination by ensuring that any water that might flow back into the system is kept away from the clean water supply.

By maintaining this gap, it is impossible for contaminants from wastewater or sewage to siphon back into the drinking water supply during pressure fluctuations or system failures. This feature is particularly important in areas where the risk of backflow is high, such as in the case of appliances that can introduce waste into the water supply.

While aspects such as enhancing water pressure or supporting pipe connections are important in plumbing systems, they do not relate to the critical function of the air gap, which is solely focused on safeguarding public health through backflow prevention. Allowing for drainage also does not align with the air gap's purpose, as drainage relies on gravity and proper pipe design, whereas an air gap is a preventive measure against contamination.