Plumbing is licensed in nearly every state for a reason that predates modern construction codes: plumbing protects the public water supply. Cross-connections, backflow, and improper drainage can contaminate drinking water well beyond a single building, so states regulate who is allowed to do the work.
The usual tiers
- Apprentice plumber — training under supervision, logging hours toward the next level.
- Journeyman plumber — has met the experience requirement and passed an exam; performs plumbing work, often under a master or contractor.
- Master plumber — a senior credential, frequently required to pull permits and take responsibility for a job.
- Plumbing contractor — the business license that lets a company contract for plumbing work, typically requiring a master plumber and proof of insurance or bond.
How to verify one
Locate the state plumbing board or the department that administers plumbing licenses, and look up the specific license. Confirm active status, the right classification for the work, and a current (not expired) date. Because some states run plumbing through a standalone board and others fold it into a broader construction or health agency, starting from a directory of the official boards saves the guesswork.
The insurance check is separate
A current plumbing license means the contractor is legally permitted to do the work; it says nothing about whether they are insured for it today. Verify a certificate of insurance on its own schedule — a license and a COI answer two different questions.