Which of the following methods of backsiphonage prevention is least effective?

The least effective method of preventing backsiphonage in this context is the barometric loop. A barometric loop functions by utilizing the elevation of the loop to create a height difference that helps combat negative pressure in a system. However, its effectiveness is highly dependent on proper installation and maintenance.

If the barometric loop is not adequately maintained or if the elevation is not sufficient, it may fail to prevent backsiphonage. Additionally, barometric loops may not be practical in all infrastructure scenarios, leading to situations where their installation would be challenging.

In contrast, options such as vacuum breakers and air gap separation provide more dependable physical barriers against backsiphonage. Vacuum breakers are designed to prevent backflow by allowing air to enter the system when negative pressure is detected, while air gap separation creates a physical barrier between the potable water supply and any potential contaminants. Backpressure units are also effective in preventing backflow under negative pressure conditions.

Thus, while the barometric loop can play a role in backsiphonage prevention, its limitations in reliability and practical application make it the least effective method compared to the other options.