What is the unobstructed vertical distance from a discharge pipe to the flood level rim of a fixture called?

The unobstructed vertical distance from a discharge pipe to the flood level rim of a fixture is referred to as an air gap. This concept is crucial in plumbing as it serves as a critical means of preventing backflow, which can contaminate the potable water supply. An air gap is essentially an unbroken vertical space that stops potential contaminants from being drawn back into the clean water supply.

For example, if the discharge pipe from a sink is located at least a certain height above the rim of the sink itself, it maintains a physical barrier that prevents any backflow from the sink into the piping system, thus safeguarding the drinking water supply. Understanding the principles of air gaps is fundamental for plumbers to ensure that installations are compliant with codes designed to protect public health by maintaining the integrity of the water supply.