Which method is considered one of the best ways to prevent back siphonage?

The air gap is considered one of the best methods to prevent back siphonage because it creates a physical separation between the water supply system and any potential contamination source. An air gap is typically established by maintaining a vertical distance between the outlet of a pipe and the flood level of the receiving vessel, ensuring that even if a negative pressure occurs in the supply line, contaminated water cannot siphon back into the clean water supply. This method is highly effective because it eliminates the risk of backflow altogether, as gravity alone prevents any back siphoned liquid from reaching the potable water system.

While other methods, such as using a backflow preventer, also provide significant protection against backflow, they rely on mechanical components which can fail or be installed improperly. An air gap, on the other hand, is a passive and self-regulating solution that does not depend on any moving parts or maintenance, making it a highly reliable choice for preventing back siphonage in various plumbing situations.