A back-siphonage condition will most likely be the cause of?

The situation of back-siphonage occurs when there is a negative pressure or reduced pressure in the distribution system, which can create a vacuum effect that draws contaminants or water from one area into the potable water supply. This can happen during conditions such as main breaks, fire fighting activities, or when there is an abrupt demand for water that causes a drop in pressure.

When the pressure in the supply side decreases significantly, it can pull water from interconnected systems or sources, which should not normally occur, thus compromising water quality. This is why reduced pressure or negative pressure on the service or supply side is closely associated with the occurrence of back-siphonage—because it's the key factor that enables the reverse flow of water and potential contamination.

In contrast, increased flow in the distribution system, accumulation of air in the pipeline, and excessive water pressure in the main do not create the conditions necessary for back-siphonage to occur. These scenarios do not facilitate the reversal of flow that would introduce contamination into the clean water supply.