What is typically used to prevent back siphonage in plumbing systems?

An air gap is typically utilized to prevent back siphonage in plumbing systems due to its effective design, which eliminates the possibility of contaminated water being drawn back into the potable water supply. It functions by creating a physical separation between the water supply and any potential contaminants. Specifically, an air gap is established by placing the end of a water outlet (such as a faucet) above the flood level of the fixture it is filling. This design ensures that even if there is a negative pressure in the system, water cannot travel back from the fixture to the source because there is a gap filled with air that acts as a barrier.

In contrast, other devices like check valves serve to prevent backflow due to pressure differential but may not effectively address back siphonage scenarios. Conversely, a ball valve and a shut-off valve are primarily used to control water flow rather than specifically to prevent back siphonage. Thus, using an air gap is critical in maintaining the integrity of a potable water system by preventing contaminants from entering through back siphoning.