Backflow of nonpotable materials into the potable water system may occur through which methods?

Backflow of nonpotable materials into the potable water system is a serious concern in public health and sanitation. Understanding how this can occur is essential for preventing contamination.

Backpressure occurs when the pressure in a nonpotable system exceeds the pressure in the potable water system, allowing potentially dangerous substances to flow backward into the drinking water supply. This often happens in scenarios where pumps are used or when water systems are connected improperly, creating conditions that can force nonpotable water upstream.

Back-siphonage, on the other hand, is a phenomenon that can occur when there is a drop in pressure in the potable water system, such as when there are water main breaks or high demand periods. This negative pressure can create a vacuum effect that draws water from the nonpotable source into the drinking water supply, leading to contamination.

Both of these mechanisms—backpressure and back-siphonage—are critical pathways that can lead to the unintended entry of nonpotable materials into the potable water system, which is why they are correctly identified as methods through which backflow can occur. The selection of "A and B above" recognizes the significance of both methods in the context of public health protection against waterborne illnesses.