What must be maintained to prevent backflow into the potable water supply?

The correct answer is maintaining positive pressure to prevent backflow into the potable water supply. This concept is rooted in the principles of hydraulic pressure and water dynamics. In a plumbing system, maintaining positive pressure ensures that the potable water is pushed through the system rather than being drawn back into it from source areas that may be contaminated.

When positive pressure is present, it reduces the likelihood that contaminated water from a non-potable source can flow back into the clean supply. For instance, if there is a cross-connection between the potable and non-potable systems, negative pressure or a total vacuum could potentially siphon contaminated water back into the supply. Conversely, with positive pressure, the flow of water will always move in the intended direction—from the drinking water source to the tap, effectively keeping potential contaminants at bay.

While other measures like air gaps can also help maintain the safety of drinking water, they are separate methods rather than directly related to maintaining pressure within the system. An air gap creates a physical separation that can help prevent backflow, but it does not address the need for a consistent pressure balance in the system.