Double Check Valve Assembly: When Is It Required
If you manage a commercial building, an irrigation system, or a multi-family property, there is a good chance you have heard the term "double check valve assembly" come up during a plumbing inspection or a water utility notice. It is one of the most commonly required backflow prevention devices in the United States — and one of the most misunderstood. Understanding when it is required, and why, can save you from compliance violations and protect the people who use your water supply.
A licensed plumber inspecting a double check valve assembly mounted on an underground irrigation service line outside a commercial building
What Is a Double Check Valve Assembly?
A double check valve assembly, often abbreviated DCVA or DC, is a mechanical device installed on a water supply line to prevent water from flowing backwards into the public water main. It consists of two independently acting, spring-loaded check valves housed in a single body, along with two shutoff valves and test cocks that allow a certified tester to verify that the device is functioning correctly.
The key word in its design is "double." If one check valve fails, the second provides a backup layer of protection. This redundancy makes it a reliable and widely accepted solution for many common cross-connection scenarios — situations where a potable water line connects to a non-potable source, creating a pathway for contamination if pressure conditions change.
Unlike a reduced pressure zone (RPZ) assembly, a DCVA does not include a pressure differential relief valve. This makes it a lower-profile device that can be installed underground or in tight mechanical rooms, which is one reason it is popular for irrigation and fire suppression applications. However, that also means it is only appropriate for low-to-moderate hazard situations, not for connections involving toxic chemicals or high-hazard fluids.
Low-Hazard vs. High-Hazard Applications
Water utilities and plumbing codes classify cross-connection hazards on a spectrum. A high-hazard connection involves substances that could cause illness, injury, or death if they entered the drinking water supply — chemicals, pesticides, medical fluids, and similar contaminants. For high-hazard applications, an RPZ assembly is almost always required.
A double check valve assembly is designed for low-to-moderate hazard scenarios, where the contaminant risk involves water quality degradation rather than immediate health threats. Common examples include:
- Irrigation systems serving residential lawns, commercial landscaping, or parks, where the primary concern is fertilizer or pesticide backflow
- Fire suppression systems with potable water supplies and no chemical additives
- Booster pump systems in multi-story buildings where the secondary water circuit does not involve hazardous substances
- Food service facilities where non-chemical water equipment is connected to the supply line
- Apartment complexes and HOAs with shared water infrastructure and irrigation tie-ins
- Car washes with standard soap and water systems, depending on jurisdiction
If your property falls into any of these categories, there is a strong chance your utility or local plumbing code requires a DCVA — or already requires you to test the one you have on file.
Diagram view of a double check valve assembly cross-section showing two spring-loaded check valves, shutoff handles, and test cock ports in a cutaway illustration style
Who Decides Whether You Need One?
The requirement for a double check valve assembly can come from several sources, and understanding which applies to your situation is important.
Your water utility is usually the primary authority. Most utilities operate cross-connection control programs that dictate which type of backflow preventer is required based on the service type and the hazard level of your property's plumbing. When you apply for a water service connection — or when your utility conducts a cross-connection survey — they will specify the appropriate assembly. Failure to install the required device, or failure to have it tested on schedule, can result in fines or service shutoff.
State plumbing codes often adopt or reference the Uniform Plumbing Code (UPC) or International Plumbing Code (IPC), both of which include detailed cross-connection control requirements. These codes specify minimum device standards based on the type of connection and the hazard classification.
Local building departments may add requirements on top of state code when issuing permits for new construction or renovations. If you are adding an irrigation system or retooling your fire suppression infrastructure, a permit review will typically identify whether a DCVA or a higher-rated device is required.
When in doubt, contact your water utility's cross-connection control department. They maintain lists of approved assemblies and can clarify exactly what your property requires.
Testing and Maintenance Requirements
A double check valve assembly is not a set-it-and-forget-it device. Most jurisdictions require annual testing by a certified backflow tester — someone licensed by the state or trained to a recognized standard such as those set by the American Water Works Association (AWWA) or the USC Foundation for Cross-Connection Control.
During a test, the technician will isolate the assembly, attach differential pressure gauges to the test cocks, and check that each check valve holds a minimum differential pressure. If either valve fails to hold, the assembly must be repaired or replaced before it is returned to service. The tester submits a report to your water utility, which keeps compliance records on file.
Property managers should maintain their own records as well — test reports, repair invoices, and installation documentation. If your utility issues a compliance notice, having clean records is your first line of defense.
A certified backflow tester in work gear using differential pressure test gauges on a double check valve assembly mounted on a building's main water entry line
Common Mistakes Property Owners Make
One of the most frequent issues utilities encounter is property owners installing the wrong device. A DCVA installed where an RPZ is required does not satisfy the hazard requirement, even if it is properly tested. Always confirm the hazard classification of your cross-connection before purchasing equipment.
Another common mistake is neglecting underground assemblies. If your DCVA is buried in a vault serving an irrigation system, it is easy to forget about until a compliance notice arrives. Schedule annual testing at the same time you activate your irrigation system each spring so it stays top of mind.
Finally, some property owners attempt to self-test or skip testing during years when their property is not actively using the connected system. Most utilities do not grant exemptions for inactive connections — if the device is installed on an active service line, it must be tested.
Understanding the double check valve assembly and its appropriate applications puts you in a stronger position to manage compliance, protect your tenants and occupants, and avoid the frustration of last-minute notices from your water utility. When in doubt, work with a certified backflow tester who knows your local requirements.
Sources
U.S. Environmental Protection Agency — Cross-Connection Control Manual (EPA 816-R-03-002). Provides foundational guidance on backflow prevention device selection and hazard classification for water systems.
American Water Works Association (AWWA) — Manual M14: Recommended Practice for Backflow Prevention and Cross-Connection Control, Fourth Edition. The industry standard reference for utilities and property owners on assembly selection, installation, and testing requirements.
USC Foundation for Cross-Connection Control and Hydraulic Research — Manual of Cross-Connection Control, Tenth Edition. University of Southern California's authoritative guide used by certifying bodies and regulators nationwide to establish device approval standards and testing protocols.