This Is One Place You Should Never Install a Backflow Preventer

If you’re still installing backflow preventers in utility vaults, it’s time for a change. None of us like change. We get it. Especially when there’s no need. After all, “If it ain’t broke, don’t fix it,” right?

But we’ve traveled all over the United States and are learning more every day about backflow design. We’re regularly meeting with water jurisdictions and civil engineers. We’re talking with backflow device manufacturers and trade groups, including ABPA and AWWA. We’re listening to what the University of Southern California’s Foundation for Cross-Connection Control and Hydraulic Research has to say on the subject.

All of this led us to two compelling reasons why you should keep backflow preventers out of underground utility vaults.

A flooded Utility vault creates a potential cross-connection

Water jurisdictions often tell us they know a vault can flood. In fact, 70 percent of water purveyors and engineers admitted as much in a Safe-T-Cover poll. Some water officials say at least half the vaults they inspect have water in them.

One Texas backflow tester sends us pictures and videos of flooded vaults. We also interviewed a Virginia-based tester and instructor. He says 100 percent of the vaults he works on have flooded at least once.

A cross-connection control investigator in a large midwestern city told us something very scary. He says he’s opened thousands of vaults during his 30-year career and only one out of 100 is dry. And when the vault floods, the backflow prevention device is often completely under water.

Experts at USC write about the dangers of flooded utility vaults in their publication, Cross Talk. They recommend all backflow prevention assemblies be installed above-grade. Double-check valve assemblies are often installed below-grade to prevent freezing, but typically end up underwater in a flooded vault.  

Those same experts state DC and RPZ must be installed between 12 and 36 inches above-grade because a backflow preventer installed in a vault or pit is exposed to a flooding risk. Then there's the possibility of contaminated water, creating a cross-connection between the water in the pit and the backflow preventer through the test cocks. This will occur whether the test cocks are opened or closed.

Their conclusion: USC recommended placing backflow prevention installations in an aluminum enclosure. The benefits of using an outdoor backflow enclosure include:

• Discretion: Can be easily hidden

• Protection against freezing

• Security: Keeps thieves and vandals away

Outdoor backflow enclosures reduce the risk of a cross-connection. Yet, test cocks found on a DC could be the site of a cross-connection: if a test cock leaks or is broken off and submerges, backflow could occur through the test cock. So, instead of preventing backflow, a cross-connection gets created through the assembly!

Additionally, every state requires each water jurisdiction to have a cross-connection control program with language similar to this: Each public water supply shall develop a comprehensive, ongoing program for the detection, elimination, and prevention of cross connections.

If vaults can create a cross-connection, how are they in compliance with this requirement? Knowing this, why would the vault ever be an acceptable design if the responsibility is to provide a design that prevents cross-connections and safeguards clean drinking water?

For more evidence of how often vaults flood, take a look at the video below sent to Safe-T-Cover by testers:

Water Utility Vaults Are Dangerous

OSHA considers water utility vaults or pits confined spaces. Statistics from the National Institute for Occupational Safety and Health show an average of 92 fatal injuries in confined spaces each year.

You might be thinking, These testers are trained professionals, surely they know how to manage a confined space. That’s true, but what about the building's maintenance person, the property owner, or adventurous kids that can get in the vault by just opening the lid?

Testers agree that there is little stopping curious people from opening and accessing a vault.

The two main reasons engineers and water districts have historically cited for installing backflow preventers in vaults are heating and aesthetics. In terms of backflow enclosure aesthetics, all that is required is thoughtful placement on the grounds and possibly some landscaping or custom colors or graphics.

What's more, backflow enclosures that meet the ASSE 100 Class 1 standard are heated and insulated. Knowing this, why would you continue to design vaults for backflows when an above-ground enclosure is an already accepted design in most states and cities across the nation?

Change Your Approach to Backflow Preventer Installations

We see installing backflow preventers in a water utility vault as a clear problem. Unfortunately, the utility vault has been the standard for backflow design for decades.

We now know using an above-ground backflow enclosure should replace the vault. Change in any industry can be hard, but it's in everyone's best interest to protect potable water supplies, irrigation systems, sprinkler systems, fire hydrants and water lines by placing backflow preventer installations in backflow enclosures.

For more information, check out our Engineer's Guide to Industrial Enclosure Design. Or download our checklist below to help get you started.

The civil engineering community is already implementing changes. Now, it’s your turn. Contact the Safe-T-Cover team if we can provide support or help you on your next project.