What phenomenon is caused by a vacuum in the distribution system due to a lack of positive pressure?

The phenomenon caused by a vacuum in the distribution system due to a lack of positive pressure is backsiphonage. Backsiphonage occurs when there is a sudden drop in pressure within the water distribution system, creating a vacuum or negative pressure that can pull contaminants from the surrounding environment back into the potable water supply. This situation typically arises when there's a break in a water main or when a high demand for water leads to a significant drop in pressure.

When backsiphonage occurs, it poses a serious risk to water quality because it can allow substances, including pathogens and chemicals, to enter the drinking water supply. Understanding this phenomenon is crucial for water operators to implement proper measures to maintain positive pressure in the distribution system and prevent contamination, which is vital for public health and safety.