Backflow preventer testing in Charles County, Maryland.
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Charles County runs its own water utility through the Department of Public Works, and the rule for backflow assemblies lives on its Cross Connection Control Program page. The sentence that matters reads: the State of Maryland requires all testable backflow assemblies, including those used on irrigation systems, to be tested on an annual basis as a minimum. The page quotes the state law behind the tester rule too, Business Occupations and Professions Article 12-306(c)(2), under which only a master plumber or journey plumber possessing certification may certify the installation and testing of mechanical cross connection control devices. The county keeps a courtesy list, Registered Backflow Testers, of firms registered with it to install, test and repair assemblies, with a disclaimer that it sets no pricing and suggests getting several estimates.
The county’s page is built around irrigation, because that is where it has been strict. Charles County requires an ASSE 1013 reduced pressure zone assembly on every irrigation system, no longer permits the cheaper pressure vacuum breaker, and will not let an irrigation system go into service until the assembly has passed its annual test. A failed assembly has to be repaired or replaced and retested before the system runs again, and an irrigation line the owner has given up on has to be physically disconnected and capped; a winterized system does not count as disconnected, and the county asks for verification of a removed assembly. New irrigation installs need a backflow permit from the Department of Planning and Growth Management and a plumber registered with the county.
Fire sprinklers sit under the same annual sentence without a paragraph of their own. The county’s rule covers all testable backflow assemblies, and a standalone 13D system in a St. Charles or Waldorf townhome that was built with a testable double check on the sprinkler branch is one of them. A multipurpose system that runs the heads off the house plumbing, and a standalone system the builder fitted with a plain non-testable dual check, have nothing to test; we tell you which you have on the first visit rather than bill a test that the device cannot take. Homes on wells south of La Plata and through the rural county have no utility connection and no backflow assembly in this sense at all; their water story is on the well-water page.
The test, the tag, and what a failure costs in Charles County
A certified tester isolates the assembly, connects a calibrated gauge to the test cocks, checks each check valve for tightness and the relief valve on a reduced pressure assembly, then tags the body with the date and result and records it with the county program. The whole visit is under an hour and our price for it is flat, under $150, which is in line with what other Maryland firms publish: TLC Incorporated in Gambrills lists most Maryland tests at $75 to $200. When a device fails, the fix is a rebuild kit when the body is sound and a replacement when it is cracked, corroded, out of parts or has failed twice. Published Maryland plumber ranges for that work run $100 to $500 for repairs at TLC and, at Baltimore Plumber Service, $600 to $1,200 for a new or upgraded device and $1,500 to $3,000 for a full replacement. Our quote comes first, in writing, and the retest after the fix is recorded as its own result. The county’s Cross Connection Control office is at 5310 Hawthorne Road in La Plata, 301-609-5606, for questions about your own record; the rebuild or replace decision is walked through in backflow preventer replacement.
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 Charles County page.
What people ask before they book
Who requires the backflow test in Charles County, the county or the state?
Both, in the county’s own words. The county program page says the State of Maryland requires all testable backflow assemblies to be tested at least annually, and the county program administers that locally, keeps the list of registered testers and issues the permits. The county, through DPW Utilities, is who you deal with.
My Waldorf townhome has a 13D system. Does it have a testable assembly?
Sometimes. Standalone systems built with a double check that has test cocks do; multipurpose systems and standalone systems with a plain dual check do not. It takes a minute to tell at the valve. If there is nothing testable, there is no annual test, and we say so.
What does the county do if an irrigation assembly fails?
The irrigation system cannot be used until the assembly is repaired or replaced and passes a retest. If you would rather drop the irrigation, the county requires the assembly to be physically disconnected and the pipe capped, and it asks for verification. Winterizing the system is not the same as disconnecting it.
Read before you book
- Backflow preventer testing and replacement in Baltimore: the metro water letter, the fire sprinkler assembly, and what happens when the test fails6 min read
- Backflow preventer replacement: when testing is not enough5 min read
- ADU fire sprinkler requirement in Charles County: Bill 2026-06 and the detached cottage7 min read
- Recalled sprinkler heads are still in Prince Georgeâs County ceilings5 min read