Backflow is the reversal of water flow into the city's potable water system, which can present a risk to drinking water. Backflow prevention keeps drinking water clean and safe for our community.

Backflow Prevention Program

State regulations require the City of Boulder to maintain a Backflow Prevention Program to track the installation and annual testing of backflow prevention assemblies on all hazardous cross-connections (potential points for contamination and backflow).

Backflow Web Portal Information

All annual test reports for backflow assemblies must be submitted online by a certified tester.

Does My Property Need Backflow Prevention?


Residential single-family customers/homeowners do not have to comply with the Backflow Prevention Program requirements unless:

  • There is an auxiliary water source on the property;
  • There is a dedicated irrigation line tapped off of the main; or
  • There is another hazard as identified by the Backflow Prevention Program (including the existence of a well on the property).

The Backflow Prevention Program requirements are not meant to contradict building, fire or plumbing codes, which may require a residence to have a backflow prevention assembly like those required on residential sprinkler systems. When backflow prevention assemblies are otherwise required, they must be installed, but will not be tracked by the Backflow Prevention Program.


Multi-family properties include two or more separate dwelling units served by one meter connection.

  • Multi-family properties with nine or more dwelling units must comply with backflow prevention installation and annual testing requirements.
  • Multi-family properties with eight or fewer dwelling units may qualify for an exemption from the city’s backflow prevention installation and testing requirements. Properties must meet all of the criteria listed on the Small Multi-Family Exemption Application to qualify. View our FAQs for more information.


Commercial properties must comply with backflow prevention assembly installation and annual testing requirements.

General Compliance Information

All properties as described above must comply with state regulations for the installation and annual testing of backflow prevention assemblies.

View information on installation criteria and/or which backflow prevention assemblies are required to be installed and tested annually. City staff may need to survey properties to determine whether cross-connections are present, what the degree of hazard is or if approved assemblies are installed in proper locations.

The city’s Backflow Prevention Program tracks the installation and annual testing of "containment" assemblies. Containment assemblies must be installed after the meter but prior to any plumbing branches. It is possible that two containment assemblies may be required.

Other assemblies may be required inside a property by plumbing code. These are called "isolation" assemblies because they isolate internal hazards. In most cases the city does not track these assemblies. It is strongly recommended that isolation assemblies are tested annually along with containment assemblies as they can keep water inside the property safe for consumption.

Irrigation and Pressure Vacuum Breakers

Pressure vacuum breakers that are currently being used for backflow prevention on dedicated irrigation lines are acceptable as long as the assembly passes annual tests. If a pressure vacuum breaker fails and requires replacement, it must be replaced with a Reduced Pressure Zone assembly. See City of Boulder Design and Construction Standards 5.09(c)(4) for additional information.

Test Your Backflow Prevention Assemblies

What is a backflow assembly test?

Backflow prevention assemblies are tested by certified testers who use gauges to either add or relieve pressure to determine if they are working properly. This information is recorded on a test report for each assembly. These tests are required annually per state regulations.

Find an assembly tester

Testers must hold a current certification from either The American Backflow Prevention Association or The American Society of Sanitary Engineers. Contact a plumber or contractor to find someone who can test your assembly. The city does not have a list of recommended testers.

If your existing backflow prevention assembly has been tested before, it should have a tag from the previous tester that shows the tester’s contact information.

Assemblies on fire lines

Submit test reports

Testers or owners are required to submit annual test reports to the Backflow Prevention Program via the online portal within 10 days of the test.

Water suppliers, testers and customers must all retain test report records for three years.

Check the status of your test report

Customers should request confirmation from their certified tester that all device test report(s) for the property have been submitted through the city’s backflow portal.

Failing tests

The Backflow Prevention Program must be verbally notified the day the failing test is taken, and the failing test should be submitted to the city’s online portal within three days.

Failed assemblies must be repaired and/or replaced immediately. If they cannot, the Backflow Prevention Program must be notified, and a compliance plan must be established.

A failed test can result in suspension of water service if the Backflow Prevention Program determines the cross-connection represents an immediate risk to public health.

Failure to Comply

Failure to install a required backflow device or get all devices on a property tested on an annual basis may result in water service shut-off or up to a $1,000 fine.

The city is responsible for ensuring full compliance with State of Colorado backflow prevention requirements. If the city does not meet state regulations, the city’s water supply is at risk and the city may be required to notify all City of Boulder water customers that we have violated state regulations.