Backflow of nonpotable materials into a potable water system may occur due to which of the following?

The correct answer encompasses both backpressure and backsiphonage as mechanisms through which backflow of nonpotable materials into a potable water system can occur.

Backpressure is a situation where the pressure in a nonpotable system exceeds that in the potable water system. This can happen when there is a change in the pressure differential, enabling nonpotable water to flow back into the potable system. It is crucial to control systems and prevent conditions that could create backpressure to ensure the integrity of potable water sources.

Backsiphonage, on the other hand, occurs when there is a drop in pressure in the potable system, creating a vacuum effect that pulls nonpotable water back into the potable supply. This often happens due to events like main breaks, high-demand water usage, or fire hydrant usage that lower the pressure in the distribution system.

Both of these phenomena pose significant risks to public health, which is why understanding them is essential for maintaining safe water supplies. Proper cross-connection control measures are implemented to mitigate these risks and ensure that the potable water systems remain uncontaminated.