INFORMATION ON CROSS-CONNECTION AND BACKFLOW PREVENTION
What is a cross-connection?
A cross-connection is any temporary or permanent connection between a public water system or consumer's potable
(i.e., drinking) water system and any source or system containing non-potable water or other substances.
An example is the piping between a public water system or consumer's potable water system and an auxiliary
water system (including wells), cooling system, or irrigation system.
What is backflow?
Backflow is the undesirable reversal of flow of non-potable water or other substances through a cross-connection
and into the piping of a public water system or consumer's potable water system. There are two types of backflow:
backpressure backflow and back-siphonage. Backpressure backflow is backflow caused by a downstream pressure that
is greater than the upstream or supply pressure in a public water system or consumer's potable water system.
Backsiphonage is backflow caused by a negative pressure in the water mains, causing water to flow from a customers
water system back into the public water mains.
What is a backflow preventer?
A backflow preventer is a method or mechanism to prevent backflow. The basic method of preventing backflow is an
air gap, which is a physical separation of the public water mains and the customers plumbing equal to two diameters
of the two pipes(this gap must be at least 1 inch).
eliminates a cross-connection by provides a physical barrier to backflow. The basic mechanism for
preventing backflow is a mechanical backflow preventer, which provides a physical barrier to backflow.
What types of backflow assemblies, devices and methods are permitted?
The following are types of permitted assemblies, devices and methods: Air Gap, Atmospheric Vacuum Breaker,
Double Check Valve Assembly, Pressure Vacuum Breaker Assembly, and Reduced Pressure Principle Backflow
Prevention Assembly. The choice of device or method depends on the type of cross connection hazard that is present.
Why do backflow preventers have to be tested periodically?
Mechanical backflow preventers have internal seals, springs, and moving parts that are subject to fouling,
wear, or fatigue. Also, mechanical backflow preventers and air gaps can be bypassed. Therefore, all backflow
preventers have to be tested annually to ensure that they are functioning properly.
Specific Information about a Hose Bibb Atmospheric Vacuum Breaker
A hose bib vacuum breaker should be attached to all threaded hose bibs to which a hose can be connected
(unless it has a built-in vacuum breaker); Cross-connections with hoses are probably the most prevalent
cause of backflow and the contamination of the water system. These devices do not protect against back
pressure, only siphonage. They should be installed above the level of the hose being used on it and not
put under continuous pressure (more than 12 hours at a time)
For more information contact SUD General Manager Ben Beavers (931) 598-5611.
