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A cross connection is a piping arrangement that allows a potable water system to be connected to a source of potential pollution or contamination. The most common example is a garden hose attached to a hose bib, with the end of the hose connected to a pesticide sprayer. A drop in water pressure in the supply main can cause these chemicals to be pulled back into the water supply (backflow), contaminating a building or even a neighborhood. The contaminant then poses a risk for anyone using the water for drinking, cooking, bathing or other purposes.

Water that flows opposite its normal direction is called backflow. It is vital to protect cross connections to prevent backflow into potable water. Improper plumbing or cross connections on private property can contaminate the public drinking water supply. If there is an incident that results in contamination of public drinking water, the owner or occupant of the property can be held liable for damages. 

Backflow is caused by backsiphonage and backpressure.


Backsiphonage is caused by negative pressure (vacuum or partial vacuum) in the supplying water pipe. It can be created when there is a disruption in the water supply due to nearby fire-fighting, repairs or breaks in water mains, etc. The effect is similar to sipping a soda through a straw.


Backpressure is caused whenever the downstream pressure exceeds the supply pressure, which is possible in installations such as heating systems, elevated tanks, pressure producing systems and systems with downstream pumps.

Preventing backflow

Backflow conditions are potentially dangerous, but preventable. In order to comply with the Arizona Administrative Code on Backflow Prevention (R18-4-215) and the Uniform Plumbing Code (Chapter 6), property owners must do the following to prevent backflow:

  • Isolate your water system from the public's through the elimination of unnecessary cross connections.
  • Protect cross connections that cannot be eliminated with an approved backflow prevention device or assembly.
  • Conduct timely annual testing of backflow prevention assemblies on your property.

Backflow prevention devices and assemblies

Air gap

An air gap is the physical separation of the potable and non-potable system by an air space. The vertical distance between the supply pipe and the flood level rim should be two times the diameter of the supply pipe, but never less than one inch. Air gaps are frequently used on wash basins and industrial processing applications.

Atmospheric vacuum breaker (AVB)

Atmospheric vacuum breakers must be used only on connections to a non-potable system where the vacuum breaker is not subjected to backpressure. They must be installed on the discharge side of the last control valve, and a minimum of six inches above the usage point. An AVB is not to be used under continuous supply pressure for more than 12 hours. Typical applications for an AVB are lawn sprinkler systems and dishwashers.

Hose bib vacuum breaker (HBVB)

Hose bib vacuum breakers are small, inexpensive devices for hose connections that simply attach to hose bibs and threaded faucets. However, like AVBs, they cannot be used under continuous supply pressure, and can only be used where the only source of backpressure comes from an elevated hose. HBVBs are commonly used on hose bibs, service sinks and any threaded pipe to which a hose may be attached.

Pressure vacuum breaker (PVB)

Pressure vacuum breakers may be used as protection on connections to all types of non-potable systems where they are not subject to backpressure. These assemblies must be installed 12 inches above the usage point. The applications for a PVB are similar to the AVB, with the exception that they may be used under continuous supply pressure.

Double check valve assembly (DC)

A double check valve assembly may be used as protection of all direct connections through which any substance might enter the potable water system in a concentration that would constitute a nuisance or be aesthetically objectionable, such as air, steam, food or other material that does not constitute a health hazard. The DC is used where the degree of hazard is low.

Reduced pressure principle assembly (RP)

A reduced pressure principal assembly may be used on all direct connections that may be subject to backpressure or backsiphonage, and where there is the possibility of contamination that constitutes a potential health hazard. The RP is used where the degree of hazard is high. Typical applications for an RP include service lines supplying medical facilities, restaurants, laundries, auto repair facilities and premises with private wells.

Our Cross Connection Control Department

Our Cross Connection Control Department helps commercial and multi-residential property owners meet various regulatory requirements and standards in relation to backflow prevention. It's a cooperative effort between plumbing and health officials, water purveyors, property owners and certified testers. Together, we establish and administer guidelines for controlling cross connections, ensure their enforcement and make sure the public potable water supply will be protected.

The installation, maintenance and testing of the backflow prevention assemblies is the responsibility of the customer. Backflow prevention assembly installation details can be found in our Developer and Engineering Guid​e. Backflow prevention assemblies must be located within 36 inches of the water meter, unless otherwise directed by our Cross Connection Control Department. The type of backflow prevention assembly installed must meet the degree of hazard present on the premises.

Our Cross Connection Control Department:

  • Maintains a database of facilities and backflow prevention assemblies installed on the service line(s) to each premises, along with a test history of each of those assemblies and notes from inspections
  • Maintains a database of EPCOR-recognized certified testers of backflow prevention assemblies and their testing equipment calibration
  • Conducts cross connection inspections of new and existing buildings within our service districts
  • Notifies affected customers of annual testing requirements

Testing requirements

Backflow prevention assemblies must be tested by a certified backflow prevention assembly tester:

  • Upon installation
  • When cleaned, repaired or overhauled
  • When relocated
  • Annually
  • As required by the regulatory authority

See our list of certified backflow prevention assembly testers in the resources section. In addition to their tester certification and testing equipment calibration, these testing companies have also provided proof of general liability insurance of at least $1 million and their state contractor's license. If you are using a tester not on this list, you will need to provide us with proof of the tester certification and testing equipment calibration. It is the customer's responsibility to ensure that testing is complete and that the vendor used is certified to perform the testing.

Test reports must be submitted to our Cross Connection Control Department within 30 days of the test. ​​