Cross Connection & Backflow

Protecting your drinking water supply is everyone’s responsibility. State regulations require residential, commercial and industrial customers served by a public water system to protect the public water system from potential contamination. Under certain conditions water from private plumbing can flow into the public water distribution system, this is referred to as backflow. In order to prevent potential backflow, some customers are required to install and maintain backflow prevention devices on the main water service lines.

What is Cross Connection?

Cross Connection is any actual or physical connection between a potable (drinkable) water supply and any source of non-potable liquid, solid or gas that could contaminate drinking water under certain circumstances.

What is Backflow?

Backflow is the reverse flow of water or other substances into the treated drinking water distribution system. There are two types of backflow: backpressure and backsiphonage.

  • Backpressure happens when the pressure of the contaminant source exceeds the positive pressure in the water distribution main. An example would be when a drinking water supply main has a connection to a hot water boiler system that is not protected by an approved and functioning backflow preventer. If pressure in the boiler system increases to where it exceeds the pressure in the water distribution system, backflow from the boiler to the drinking water supply system may occur.  
  • Backsiphonage is caused by a negative pressure (vacuum or partial vacuum) in the water distribution system. This situation is similar in effect to the sipping of water through a straw. In the drinking water distribution system, negative pressure (backsiphonage) occurs during a water main break or when a hydrant is used for fire fighting.

Why should you be concerned?

Backflow may affect the quality of the drinking water at your home, business or facility and has the potential to create health hazards if contaminated water enters your water supply plumbing system and is used for drinking, cooking or bathing. Backflow events occur more often than you might think although most do not create health hazards. Unprotected cross-connections with water supply plumbing or public drinking water piping systems are prohibited. We are all responsible for protecting our water supply from backflow that may contaminate our drinking water. It includes complying with the plumbing code and avoiding unprotected cross connections.

Who is responsible?

The responsibility for preventing backflow is divided. In general, state and local plumbing inspectors have authority over plumbing systems within buildings while state regulatory agencies and public water suppliers regulate protection of the distribution system at each service connection. Water customers have the ultimate responsibility for properly maintaining their plumbing systems. It is the water customer’s responsibility to ensure that unprotected cross-connections are not created and that any required backflow prevention devices are tested in accordance with state requirements and maintained in operable condition.

Preventing backflow situations in your home and business

  • Be aware of cross connections, eliminate or isolate them
  • Maintain air gaps on sinks and when using hoses.
  • Do not submerge hoses or place them where they could become submerged.
  • Use hose bib vacuum breakers on fixtures (hose connections in the basement, laundry room, and on outside faucets/spigots).
  • Install approved backflow prevention devices on lawn irrigation systems and on fire sprinkler system services. Types of preventative required devices are determined based on the potential type of pollutants or contaminants high, low or moderate. In low hazard situations, the installation of a residential dual-check device might be allowed.

Failure to comply can result in water service disconnection after repeated request from our Cross Connection Department. 

Frequently Asked Questions and Answers About Cross Connection
and Backflow Prevention

I received a cross connection survey on my water usage at my facility. What is this about? 

We conduct periodic surveys of their customers’ use of water to identify and eliminate possible sources of cross connections to help ensure the safety of the public water supply. The information collected through the surveys helps to identify where backflow prevention devices may be needed as well as providing information on existing devices that may not have been previously submitted to the water company.

If I cannot get my device tested in time to meet the required deadline what should I do?

Please email our Cross Connection Department for possible extensions and/or resolution.

Who pays for the testing and how much does it cost?

It is the responsibility of the property owner and /or the ratepayer to pay for any testing and/or required repairs to the backflow device. Cost will vary with existing device location conditions and type of device. Please review pricing requirements with the selected test company/tester before having the test performed.

How often do I have to have my backflow device tested?

Backflow devices are required to be tested upon installation and at annual intervals thereafter.

I have an in ground lawn sprinkler system at my residence. Am I required to have a backflow device and have it tested?

Inground sprinkler systems are required to have a backflow prevention device installed on the water line servicing the system. The backflow device must also be periodically tested in accordance with the state testing requirements.


Survey for non-residential customers
Complete our survey and fax it back to us. We will help determine whether you are in compliance with cross-connection/backflow prevention regulations.

Fact Sheet: Definition of backflow and cross connection
Fact Sheet: Cross connection control requirements
Fact Sheet: Ways to protect from backflow
Fact Sheet: Cross connection sites and recommended backflow preventers
Fact Sheet: Residential customer requirements

Contact information

Office phone number: 703-447-3133
Fax number: 703-836-6652
Email Address: