Which of the following is the more common and least expensive method of backflow control?

The air gap separation is recognized as the more common and least expensive method of backflow control due to its simplicity and effectiveness. An air gap is essentially a vertical space between the water outlet and the flood level of a fixture, which prevents any backflow from entering the potable water supply. This physical separation ensures that contaminants cannot flow back into the supply line because there's no direct connection, and it is also a passive solution that requires minimal maintenance or active mechanical components.

In comparison, other methods like vacuum breakers and backflow preventers, while also effective, involve components that can be more costly and may require more extensive installation. Vacuum breakers are designed to prevent back-siphonage, but they may not be suitable for all applications and can malfunction if not properly maintained. Backflow preventers, especially those designed for pressure and non-pressure applications, may be more expensive due to their complexity and the need for regular testing and maintenance to ensure they function correctly.

Barometric loops are a specialized form of backflow control that can be effective in certain situations, but they require more design considerations and are typically used in specific contexts, making them less common for general backflow prevention purposes.

Overall, the air gap provides a straightforward and reliable means of preventing backflow