A licensed plumber holds the license a state or city government requires to work legally; a certified plumber holds a voluntary industry credential, such as an ASSE backflow or medical gas certification, on top of it.
“Certified plumber” doesn't name one specific credential — the usual path is to get licensed, then add the certifications the work you want calls for.
What licensing means for plumbers
The difference between a certified plumber and a licensed plumber starts with who issues the credential.
A plumbing license is legal permission: a government — your state's licensing board, or the city or county that handles licensing where you live — authorizes you to do plumbing work in its jurisdiction.
Each government sets its own rules: the rungs, the experience it demands and the exams it gives.
Whether a license carries over when you move is something our research did not confirm — check with the licensing board in the state you are moving to before you count on it.
Licensing is the layer with legal force, so it is the layer to get right first.
The full ladder — what each level may legally do, the plumbing license requirements in your state, the hours and the exams — is its own topic.
What certification means for plumbers
Most plumbing certifications, such as ASSE's, are industry credentials, not government ones: an industry organization tests a specialty skill and certifies that you passed.
An OSHA 10/30 card is a course completion card, not a certification; ASSE credentials are voluntary industry credentials, not government licenses.
In plumbing, ASSE International publishes professional-qualification standards: its Series 5000 covers cross-connection control — the 5110 credential is for Backflow Prevention Assembly Testers — and its Series 6000 covers medical gas, where 6010 is the installer credential.
These are separate certifications.
Renewal is part of the deal: ASSE certifications must be renewed every three years, and recertifying up to six months early loses no time.
A backflow tester can also answer to a state or water utility, and those bodies set their own renewal schedules — so check both the certifier's rules and your state's.
Here is the contrast in one view:
| License | Certification | |
|---|---|---|
| Who issues it | A state or city government — a licensing board, or the city or county where licensing is local | Usually an industry organization, such as ASSE International; some states issue their own tester certificates |
| What it gives you | Legal permission to work — the credential the law enforces | Proof of a specialty skill, verified by the certifier |
| Is it required? | Yes, where the jurisdiction requires it for the work | Voluntary — unless a state or water utility mandates it |
Which one you need
Which one you need depends on who is asking.
For the law, the answer is the license: the credential a government requires and enforces where you work.
For the work itself, certifications decide what you can take on — and once you are licensed, they are additions you choose rather than requirements, unless a state or water utility mandates one.
So “how do I become a certified plumber” is really a two-step answer — the usual path is to get licensed, then add certifications:
- Get licensed the way your jurisdiction requires — the rungs, hours and exams are set by your state's licensing board, or by your city or county where licensing is local
- Check whether your target work has a legally mandated credential — backflow testing, for example
- Earn the industry certification the work calls for — e.g. ASSE 5110 for backflow testing where your state or utility accepts it, ASSE 6010 for medical gas
- Keep both current — the license renews on your licensing authority's cycle; ASSE certifications every three years
Backflow testing shows how thin the line between the two can get.
Texas issues its own state backflow tester license through TCEQ (the BPAT); Minnesota requires backflow testers to hold ASSE 5110; and Washington's PL30 plumber credential requires a Department of Health tester certificate.
Same work, three different answers — which is why you confirm your own state's arrangement before assuming a certification is or is not required.
Verify before you book a course
Certifications that add pay
Our research has no verified figure for any certification premium.
Where a certification can matter is access to work: some states and water utilities require a credential for backflow testing (e.g. Minnesota requires ASSE 5110), and some states regulate medical gas work — so check what employers in your market ask for.
Two examples: ASSE 5110, the Backflow Prevention Assembly Tester credential in ASSE's Series 5000, and ASSE 6010, the medical gas installer credential in Series 6000.
They are maintained investments, not one-off badges: ASSE certifications renew every three years, and the 5110 recertification alone requires at least an 8-hour class, a 50-question written exam — rising to 100 questions from January 1, 2027 — and a hands-on practical exam.
No credential sets its own dollar value, and our research has no verified figure for what any certification adds to a paycheck — so treat any premium number you see quoted with suspicion.
The detail is on our guide to plumbing certifications worth getting, the openings that ask for them are in current plumber jobs, and where the trade's pay sits overall, our plumber salary data has the BLS figures.
Apply the same test to every other badge you are offered, including “green plumber” programs and manufacturer cards: ask who issues it — a government or a company — and whether anyone with authority actually requires it.
A voluntary credential is not a government license, and it does not substitute for one.
This page is career information, not legal advice — licensing and certification requirements change, so confirm the current rules with your state licensing board, or the city or county where licensing is local.