Key Cross-Connection Terms and Definitions

Cross-connection Any actual or potential connection between the public water supply and a source of contamination or pollution.

Backflow The flow of water or other liquids, mixtures, or substances into the distributing pipes of a potable supply of water from any source or sources other than its intended source. Backsiphonage is one type of backflow.

Backpressure Backflow that occurs when the pressure in an unprotected downstream piping system exceeds the pressure in the supply piping.

Backsiphonage Resulting from negative pressures in the distributing pipes of a potable water supply.

Where Can Cross-Connections Occur?

Cross-connections can occur at many points throughout a distribution system and a community's plumbing infrastructure. Cross-connections can be identified by looking for physical interconnections (or arrangements) between a customer's plumbing and the water system. Some specific examples of backflow incidents that can occur are:

• Lawn chemicals backflowing (backsiphoning) through a garden hose into indoor plumbing and potentially into the distribution system.
• Backsiphonage of "blue water" from a toilet into a building's water supply.
• Carbonated water from a restaurant's soda dispenser entering a water system due to backpressure.
• Backsiphonage of chemicals from industrial buildings into distribution system mains.
• Backflow of boiler corrosion control chemicals into an office building's water supply.