Actual and Potential Cross-Connections
In the definitions of a cross-connection, actual or potential cross-connections are mentioned as well as temporary or permanent cross-connections.
What is an actual or potential cross-connection?
The illustration shows an unprotected actual cross-connection and protected potential cross-connections. The one on the left is a submerged inlet and is considered an unprotected cross-connection because the end of the faucet is below the flood level rim. The one on the right is a protected potential cross-connection. The method used to control the cross-connection is an Air Gap. The air gap prevents the non-potable water from entering the potable water system. It is a classified as a potential cross-connection because a cross-connection can be created by connecting a hose to the end of the faucet or spigot and submerging it below the flood level rim.
Sillcocks, hose bibbs, wall hydrants, and other water outlet openings threaded for connecting a hose, are considered potential cross-connection and shall be equipped with a hose bib vacuum breaker permanently installed at the end of the opening pursuant to plumbing codes. An atmospheric vacuum breaker may be installed instead of the hose bibb vacuum breaker. Spigots or faucets that are not threaded and where there is no possibility of connecting a hose to the end of the outlet opening only need to be air gaped.
Actual Cross-Connection
The AWWA, “Water Treatment and Distribution” – Second Edition – Principles and Practices of Water Supply and Operations, 1996, defines an actual cross-connection as one for which the connection exists at all times.
An example of an actual cross-connection would be piping to a non-potable auxiliary supply used for emergencies such as this fire tank shown in this photo. This tank is connected to the public potable water supply system and is a connection to an auxiliary non-potable ground or surface water source. The connection permanently exists therefore it is an actual cross-connection and a backflow prevention device shall be installed between the two system to prevent the auxiliary non-potable water source for entering the potable water source.
Potential Cross-Connection
The AWWA, “Water Treatment and Distribution” – Second Edition – Principles and Practices of Water Supply and Operations, 1996, defines a potential cross-connection as one for which something must be done to complete the connection.
An example of a potential cross-connection would be a hose connected to a spigot. The hose connected to the spigot is not necessarily a health hazard until it is in use. Therefore, the plumbing codes require backflow prevention device to be installed on the spigot because the end of the hose could be connected to or placed into a non-potable such as a swimming pool, chemical mixing tank, lawn irrigation system for example. Typically, the plumbing codes will require a hose bib vacuum breaker (ASSE Standard #1011) to be installed to prevent the backsiphonage of non-potable water into the potable water system. Individual conducting cross-connection surveys of facilities or individual working for the public water system should be aware that potential cross-connections need to be controlled and protection devices installed according to plumbing codes but typically a potential cross-connection would not need to be controlled by a testable backflow prevention device. What needs to be made clear to the facility owner is that there is performance and operational standards associated with some backflow prevention devices. Such as a hose bibb vacuum breaker cannot be under constant pressure for more than twelve hours. Therefore, a nozzle cannot be installed at the end of the hose while there is pressure is in the hose for long periods. The pressure would have to be released and the water turned off at the spigot. If the pressure in the hose is not released, the integrity of the hose bib vacuum breaker in questionable.