Back-siphonage may be prevented by all of the following methods except?

Back-siphonage prevention techniques are crucial in maintaining safe drinking water by preventing contaminants from entering the water supply. Barometric loops, vacuum breakers, and air gap separation are all methods recognized for effectively preventing back-siphonage through mechanisms that disrupt the potential for a vacuum to form and draw contaminated water back into the clean water supply.

A barometric loop is a plumbing fixture that creates a high-point in a piping system, allowing potential backflow to enter the atmosphere instead of the water supply. Vacuum breakers, typically installed on faucets, allow air to enter a plumbing system when a negative pressure occurs, thus preventing siphoning. Air gap separation, which involves maintaining a physical distance between the water source and any potential contaminant, is one of the most effective means to prevent back-siphonage.

In contrast, backpressure units are not specifically designed to prevent back-siphonage. Rather, they are used in certain systems to manage pressure variations and to control the flow of liquids, but they do not inherently provide a barrier to siphoning effects. This distinction is why the selected answer pertains to a method that does not serve to effectively mitigate the risk of back-siphonage.