Backflow is the reversal of water flow and contamination into the city's drinking water system from private properties. Property owners who have backflow assemblies play an important role in protecting drinking water and public health for the community.

Backflow Prevention Program

Approved backflow assemblies are required on all commercial, industrial, irrigation, fire, and multi-unit residential water lines. Generally, single-unit homes and duplexes are exempted from annual testing per state regulations, unless an identified hazard is present. Requirements are detailed in state drinking water regulations, Boulder Revised Code and Boulder’s Design and Construction Standards.

Failure to comply with backflow requirements may result in a water shut-off warning hangtag with a $58 fee (BRC 4-20-23 (g)(5)), water shut-off with a $113 fee (BRC 4-20-24), and/or additional penalties ranging from $250 to $1,500 (BRC 11-1-25 (g)).

Backflow Web Portal Information

All annual test reports for backflow assemblies must be submitted online by a certified tester. Visit the Backflow Web Portal to register, submit a test, and add a new backflow assembly. For assistance with the portal, please review the Backflow Portal FAQs or contact nobackflow@bouldercolorado.gov

Does My Property Need Backflow Prevention?

Residential

Residential single-unit 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.

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-unit

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

  • Multi-unit properties with nine or more dwelling units must comply with backflow prevention installation and annual testing requirements.
  • Multi-unit 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-Unit Exemption Application (PDF) to qualify. View the Small Multi-Unit Frequently Asked Questions (PDF) for more information.

Commercial

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

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.

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 notified within 24 hours of a failing test via submission to our online portal. Failed assemblies must be repaired and/or replaced as soon as possible. If they cannot be repaired or replaced within 30 days, the Backflow Prevention Program must be notified, and a compliance plan must be established to avoid a Notice of Violation, water shutoff and/or associated fees and penalties.

Backflow Prevention Frequently Asked Questions

Backflow is the undesired, reversed flow of water or other substances into the drinking water supply. Backflow can occur at any cross-connection between potable and non-potable water lines and can contaminate the water supply, presenting a public health risk.

Backflow can occur when there is a loss of pressure in the public water supply system, which draws the water from a private water system into the public water system. This is called back siphonage and can occur at any time, such as during a large water main break or firefighting.

Backflow can also occur when the pressure in a private system exceeds the pressure in the public distribution system, causing the normal flow to reverse. This is called backpressure and can occur for multiple reasons, such as a pump used to increase the water pressure within a building’s plumbing system to reach a higher floor.

A cross-connection is any actual or potential connection between the public drinking water system and any other system that could accidentally introduce a contaminant back into the public water supply. An example is a piping arrangement or equipment that allows the drinking water to come into contact with non-potable liquids, solids, or gases. Cross-connections can lead to contamination of the city’s drinking water supply and impact public health if not adequately protected by backflow prevention assemblies.

We typically does not track backflow assemblies at duplexes. However, for multi-unit properties with three to eight units, we have developed an application to determine whether backflow prevention is required.

Please review this small multi-unit property exemption application carefully, to determine if your property is required to comply. Email any questions to nobackflow@bouldercolorado.gov. Submitting the form does not ensure exemption and you must receive written approval of the exemption from Backflow Prevention Program staff. We may also perform an on-site cross-connection survey to assess whether an exemption can be granted. Please note that backflow assemblies may be required by plumbing code, even though the backflow program does not track them per state regulations.

There are three main types of backflow prevention assemblies. Email nobackflow@bouldercolorado.gov if you have questions about what type to install.

  • Reduced Pressure Zone (RPZ): These assemblies are the standard and are considered to provide the highest degree of protection among the testable assemblies. These assemblies will dump water, so drains must be installed and sized according to plumbing code (increasing the drain size may help prevent flooding). RPZs must be installed 12 inches above grade and will need to be protected from freezing and flooding.
  • Double Check (DC): Generally considered to protect against low hazards. These assemblies normally don’t dump water. They may be placed below grade in certain circumstances and should still be protected from freezing and flooding.
  • Pressure Vacuum Breaker (PVB): Used specifically for outdoor irrigation systems. These systems can dump water. Assemblies must be installed 12 inches above the highest sprinkler head, which cannot have continuous backpressure, and they will need to be protected from freezing and flooding.

  • Containment assemblies: We track 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 at a property.
  • Isolation assemblies: 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 backflow program 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.

Helpful resources for single-unit homes

Test backflow prevention assemblies on your irrigation system

Typically, homes with sprinkler systems have a backflow assembly installed on their irrigation system. Testing your assembly every year should keep bacteria, animal waste and fertilizers, which leach into your sprinkler pipes, out of your drinking water. If your house has a separate metered irrigation account or fire line, you are required by City and State regulations to install an approved backflow prevention assembly and have it tested annually.

Winterize your irrigation system

Properly “winterizing” your irrigation system and backflow prevention will help maintain your system, prevent leaks and protect your drinking water. Learn more about winterizing your home.

Use garden hoses safely

  • Make sure hose connections have backflow prevention,

  • Don’t submerge garden hoses in buckets/containers/pools when filling them – leave an air gap instead.

  • Disconnect, drain and store hoses out of standing water when not in use.

Protect yourself from supplemental water sources

You can protect yourself from backflow if you have other water sources, such as swimming pools, hot tubs, spas, ponds, lakes, streams, rivers, ditch water, wells, etc. You can prevent backflow by:

  • Disconnecting the water source.

  • Using an air gap.

  • Installing a backflow prevention assembly. Some supplemental water sources may require a backflow prevention assembly be installed and tracked by the city.

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