What is the main purpose of having an air gap in drainage systems?

The main purpose of having an air gap in drainage systems is to prevent backflow of contaminated water. An air gap is a physical separation between the end of a drainage pipe and the flood level of a receiving vessel, like a sink or a sewer. This separation ensures that, in the event of a pressure drop in the drainage system (which can occur during events like a sudden change in flow or blockage), contaminated water cannot siphon back into the clean water supply.

This is crucial for public health as it helps to maintain the integrity of the potable water supply by ensuring that harmful substances do not enter through backflow due to back pressure or negative pressure events. An air gap is a simple yet effective physical barrier that ensures compliance with health and safety standards for drinking water systems.