Backsiphonage is caused by...

Backsiphonage occurs when a partial vacuum in a pipeline draws water back into the system, potentially contaminating the water supply. This phenomenon can happen when there is a sudden drop in pressure within the water distribution system, often due to an unexpected event such as a water main break or a sudden increase in demand on the system.

When a partial vacuum forms, it creates a negative pressure that can pull water from devices or storage tanks connected to the water supply, especially if those connections are lower than the point of the vacuum. This is a significant concern in maintaining water quality and preventing pollution, as it can introduce contaminants into the drinking water supply.

In contrast, excessive pressure in the line could potentially lead to other issues, such as pipe bursts or leaks, but it would not cause backsiphonage. A small leak or water hammer (a pressure surge when a fluid in motion is forced to stop or change direction) are also unrelated to the phenomenon of backsiphonage, which specifically involves a drop in pressure leading to the reverse flow of water.