What is the term used for reverse water flow in a distribution system caused by a vacuum?

The term "backsiphonage" refers to the reverse flow of water in a distribution system that occurs when there is a vacuum created, typically due to a drop in pressure in the supply line. This condition can happen when water is being drawn out from a system more rapidly than it can be supplied, such as during a fire-fighting operation or a significant water main break. When a vacuum forms, it can pull contaminants from other sources through cross-connections, potentially leading to contamination of the potable water supply.

This process is distinct from other phenomena related to water flow. Backflow is a general term that encompasses any unintentional flow of water in the opposite direction, while backpressure refers to an increase in pressure in the upstream side of a water system that can also lead to backflow, but does not result specifically from a vacuum condition. The term "vacuum flow" is not a standard term used in the context of water distribution systems.

Understanding backsiphonage is crucial for ensuring water safety and preventing contamination, which is why it's important for water operators to recognize and mitigate these risks in distribution systems.