Backflow is used to describe a condition that occurs when a difference in water pressure causes contaminants to enter the municipal water distribution system and/or the customer’s water piping. The two most common kinds of backflow conditions are back
pressure, where a device such as a pump forces higher pressure water and contaminates into the distribution system against the existing system pressure, and back siphoning, where a sudden
loss of system pressure (due to a water main break or heavy demand) causes
contaminates to be drawn into the distribution system. Backflow prevention assemblies are designed
to sense these conditions and react to prevent contamination.