Montgomery County

Backflow preventer testing in Montgomery County, Maryland.

Montgomery County homes on public water are WSSC Water customers, and WSSC is the one that wants the backflow test, not the county and not the fire marshal. Its residential page, Cross-Connection Control and Backflow Prevention Information for Residential Customers, puts the rule in one sentence: the WSSC Plumbing and Fuel Gas Code requires annual testing for all installed testable backflow prevention assemblies, plus a test right after any installation, repair or relocation. For a Rockville, Germantown or Clarksburg homeowner the word that matters is testable. A testable double check assembly has test cocks on the body. A dual check does not, and WSSC treats the two differently.

Here is how that lands on sprinklered houses. WSSC says the code required homes built from 2007 to 2009 to install the testable version of a dual check valve on the fire sprinkler feed, so those houses stay in the annual cycle for as long as the testable assembly stays in place. Newer standalone 13D systems usually left the builder with a non-testable dual check, which WSSC does not test but expects rebuilt or replaced every five years. Multipurpose systems, where the heads run off the house plumbing, generally have no separate assembly at all. In-ground irrigation is the other common testable device in the county, a pressure vacuum breaker or reduced pressure assembly near the outside wall, due for its annual field test with the result reported at spring start-up.

There is no calendar date in the rule. The clock runs one year from the last passing test, and starting with its February and March 2026 Backflow Prevention Assembly Courtesy Notice, WSSC began mailing test-due advisements to customers whose records show a testable assembly. The letter is a courtesy, the test is not; the notice itself says WSSC does not do field testing and that maintaining the assembly is the customer’s responsibility. If one arrived at your Bethesda or Potomac address and you have never heard of the device, the house almost certainly has a sprinkler or irrigation feed with an assembly the builder installed and nobody has looked at since.

Who may test a backflow assembly in Montgomery County

WSSC is strict on this. Only a WSSC-licensed and registered journeyman or master plumber who is also a certified cross-connection technician may test or repair a testable assembly, and the field test result is transmitted electronically to WSSC by a registered principal master plumber. WSSC keeps a List of Plumbing Firms Providing Cross Connection-Related Services and a Find a Registered Licensed Plumber search on the same page; the firm you hire should be on one of them, and the report should be filed by the firm, not handed to you to mail. A test with no filing behind it is the most common way Montgomery homeowners end up with a second letter after paying for a first test.

The technician closes the shutoff downstream of the assembly and connects a calibrated differential gauge to the test cocks.
Each check valve is tested for tightness in turn, and on a reduced pressure assembly the relief valve opening point is read as well.
A pass gets a dated tag on the body and an electronic report to WSSC under the firm’s registration.
A fail gets a written repair or replacement quote before any work, and the retest after the fix is a new filing, not a note on the old one.

What a failed test costs in Montgomery County

The two outcomes are a rebuild and a replacement, and the distinction is the price. A check that will not seat on a common residential double check usually takes a rebuild kit, new springs, seats and rubber, and the assembly stays. Replacement is the honest answer when the body is cracked or corroded, when parts are no longer made for the model, or when a device fails again soon after a rebuild. For a sense of what Maryland plumbers publish, TLC Incorporated in Gambrills lists most Maryland backflow tests at $75 to $200 and repairs at $100 to $500, and Baltimore Plumber Service lists $600 to $1,200 for a new or upgraded residential device and $1,500 to $3,000 for a full replacement with pipework. Those are their numbers, not ours; our test is a flat price under $150 and every repair is quoted in writing first. The rebuild or replace decision in full is in our guide to backflow preventer replacement.

One Montgomery-specific option is worth knowing. WSSC allows a homeowner to swap the testable fire sprinkler assembly for a non-testable dual check valve and leave the annual cycle, but only with proof of coordination from a certified fire sprinkler contractor, filed with the WSSC Water Cross-Connection Control Program, because the change alters the engineered hydraulic design. The county Office of the Fire Marshal may have its own permit and inspection requirements on top. We do that coordination as sprinkler contractors; a plumber alone cannot sign it.

Pricing for every configuration is published on our cost guide, well-fed systems are covered on the well-water page, and the county overview lives on the Montgomery County page.

Questions Montgomery owners actually ask

WSSC sent me a backflow letter. Is it a bill or a fine?

Neither. It is the courtesy test-due advisement WSSC started mailing in 2026 to customers whose records show a testable assembly. It asks you to have the annual test done by a WSSC-registered firm; nothing is owed to WSSC. The firm’s electronic report closes the loop. Questions about the letter itself go to the Cross-Connection Control Program at 301-206-4004.

My 13D system has a plain dual check with no test ports. Do I still test it?

No. WSSC tests only testable assemblies. A non-testable dual check is instead rebuilt or replaced every five years, and WSSC lets a single-family or townhome owner do that work on a non-testable device without a permit. We check it during the annual sprinkler inspection anyway, because a dual check that seizes can starve the system.

Can the backflow test and the sprinkler inspection happen on one visit?

Yes, and in Montgomery that is the normal booking: the sprinkler system checked, the assembly tested and tagged, the WSSC filing made under our registration, and one report for your insurer. The combined visit is described on our annual inspection page.

Does the test have to be done by a certain month?

WSSC does not name a month. The assembly is due one year after its last passing test, and immediately after any repair or relocation. Irrigation assemblies get reported at spring start-up, so April and May are the busy weeks; sprinkler assemblies can be tested any month.

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