Plumbing licensing in the United States is administered state by state, and in some states city by city on top of that. There is no national plumbing license. What follows is a map of the credentials that most commonly sit outside a standard plumbing license, so you know which conversations to have with your board before you quote work you are not yet permitted to do.
It is a map, not an authority. Every item below varies by jurisdiction — sometimes enormously.
The credentials that usually stand alone
Backflow prevention assembly tester
Testing and certifying backflow prevention assemblies — RPZ, double-check, PVB and the rest — is a distinct certification in essentially every jurisdiction that requires testing at all. Holding a plumbing license does not authorize you to test and submit reports.
How it usually works: a training course and practical exam, commonly delivered through an ASSE 5110 program, a state health or environmental agency, or an AWWA section, followed by periodic recertification. Testers typically must register with the water purveyor that accepts the reports, and the test gauge itself usually has to be calibrated on an annual cycle with documentation.
Why it is worth having: testable assemblies generally require testing on a recurring schedule, which is the rare thing in plumbing — recurring, schedulable, non-emergency revenue with a built-in reminder from the water district.
Related but not the same: a cross-connection control specialist or surveyor credential covers hazard assessment and survey work, which is a different scope than testing an assembly. Some jurisdictions require both for some work.
Gas fitting
Many states license or endorse fuel-gas work separately from plumbing, and the boundary is not intuitive — in some jurisdictions a plumbing license covers gas piping to an appliance and in others it does not cover gas at all. A number of places license LP gas separately from natural gas again.
Where it bites: tankless water heater conversions. Upsizing a gas branch, and any conversation about the meter, is fuel-gas work. If your license does not cover it, that job needs a gas fitter on it regardless of how comfortable you are doing the work.
Confirm before you quote: ask your board directly which gas work your specific license class authorizes, in writing if you can get it. “Everyone around here does it” is not a defense.
Medical gas systems
Medical gas and vacuum piping in health care facilities is governed by NFPA 99, and the personnel qualifications run through the ASSE Series 6000 standards. This is the most rigidly credentialed work a plumber can touch, and the reason is straightforward: the failure mode is a patient breathing the wrong gas.
The roles are deliberately separated: ASSE 6010 covers the installer, ASSE 6020 the inspector, ASSE 6030 the verifier, and ASSE 6040 maintenance personnel. The verifier who signs off cannot be the installer — independence is the point of the structure.
Brazing is its own qualification. Medical gas brazing is performed to a qualified procedure under a nitrogen purge, with brazer qualification typically documented in accordance with ASME Boiler and Pressure Vessel Code Section IX. Being an excellent brazer is not the same as being a qualified one on paper.
If you are considering this work, start with the certifying body and the facility’s requirements, not with a bid.
Septic and onsite wastewater
Installing, repairing or pumping onsite wastewater systems is typically licensed by a state health or environmental agency rather than the plumbing board, often with soil evaluation and design as separate credentials again. A plumbing license commonly covers the building drain to a defined point and stops there.
Where that point sits — the property line, a set distance from the foundation, the tank inlet — is jurisdiction-specific and worth knowing precisely, because it is the line between your permit and somebody else’s.
Fire protection and fire sprinkler
Fire sprinkler and standpipe work is a separate licensed trade in most states, governed by its own NFPA standards, with its own contractor licensing and often its own inspection authority. A plumbing license generally does not authorize it, even though the pipe looks familiar and the fittings are in the same aisle.
Residential multipurpose systems that share piping with the domestic water system are a genuine gray area in some jurisdictions and a firmly separate trade in others. Ask specifically.
Water treatment and conditioning
Several states license water conditioning or water treatment contractors separately, and some require specific certification to install or service certain equipment. Since hard water is behind a large share of water heater failures, this comes up more often than plumbers expect — check before you add a softener to an estimate as a line item.
Apprentice, journeyman, master, and the contractor registration on top
Most states run a tiered progression with documented hours and an exam at each step, and then treat operating a business as a further requirement layered on top — contractor registration, a surety bond, proof of liability and workers’ compensation coverage, and often a qualifying master named on the license.
Two things that catch people out: reciprocity between states is partial and specific, so a license that transfers to one neighboring state may not transfer to the next; and continuing education is commonly tied to the code adoption cycle, meaning a lapse can be a lapse in your license rather than just a missed class.
What the templates on this site actually do
Worth being precise about, since the whole point of this page is the boundary.
- They document the commercial agreement. What work is included, what is excluded, what it costs, when payment is due, and what triggers a change order. That is a real and useful thing.
- They do not authorize work. A signed contract for work you are not licensed to perform is not a defense — in many states it is unenforceable and separately actionable.
- They are general, not jurisdictional. Contractor contract requirements, mandatory notice language, lien deadlines and permitted terms are state-specific and frequently mandatory. Have a local attorney review your standard agreement once.
- They do not replace permits or inspection. Nothing here changes what your AHJ requires you to pull or who has to look at it before you close a wall.
Once you are clear on scope, here is the paperwork
Quick answers
Is there a national plumbing license?
No. Plumbing licensing is administered at the state level, and many cities and counties add their own requirements on top. Reciprocity agreements exist between some states but are partial and specific — never assume a license travels.
Can I test backflow assemblies with just a plumbing license?
Almost certainly not. Backflow assembly testing is a separate certification nearly everywhere it is required, usually with its own exam, recertification cycle, registration with the water purveyor, and annual calibration of your test gauge. Contact the water purveyor that would receive your reports — they maintain the list of accepted testers.
Does my plumbing license cover gas piping?
It depends entirely on your state and your license class, and this is one of the most variable items in the trade. Some licenses cover fuel gas fully, some cover it only downstream of a defined point, and some do not cover it at all. Ask your board about your specific license class rather than relying on local custom.
How do I get into medical gas work?
Through the ASSE Series 6000 credential appropriate to the role you want — 6010 for installation is the usual entry point — plus brazer qualification, and familiarity with NFPA 99. Start with a recognized training provider and the requirements of the facilities you would be working in. This is not work to learn on a live job.
Is this page legal advice?
No. It is a general orientation to how plumbing credentials are commonly structured in the United States, written to help you know which questions to ask. Requirements vary by state and locality and change over time. Verify everything with your licensing board, your local building department, and where relevant an attorney in your state.