Minnesota plumbing license: what your plumbing contractor license lets you do and your first 30 days

Published November 3, 2026 · Rules checked November 3, 2026

• Free. The printable checklist comes by email.
• Deepsel is our product: free estimate, invoice and scheduling software for contractors (scheduling, quotes, invoicing, card payments). One section, the one before the FAQ, says where it fits.
• Not legal advice. I read every rule here in the statute, the rule, or the Department of Labor and Industry's or the city's own page or form on November 3, 2026, and each one is linked in the sources. DLI and your city have the last word.

Your plumbing contractor license lets the company take plumbing work anywhere in Minnesota, residential or commercial, of any size, as long as a master plumber is named as its responsible licensed individual and works for that company only.^{1, 2} There's no dollar limit. The license stops at contracting gas and heating work (that takes a separate $25,000 mechanical bond), the electrical side of an electric water heater, fire sprinklers and septic systems. In the first 30 days you need the $25,000 bond and liability insurance of at least $50,000 per person, $100,000 per occurrence and $10,000 property damage (both already on file if DLI issued the license), workers' comp before the first hire, your name and license number on both sides of every truck, the city license in Minneapolis or St. Paul if you'll work there, and a check of who issues the permit in every town you work.^{3, 4}

The whole 30-day list is further down this page. It also comes as a printable sheet with blanks for your license, bond and policy numbers, your city licenses and your renewal dates. Get it three ways: make your own copy in Google Docs (lands in your Drive), download the Word version (.docx), or download the PDF. Pick a format, enter your email and I'll send the links.

One plumber put the moment well on Reddit: "I just got my master license and im trying to figure out if i can get a raise at my company or try to go on my own, super stressful."⁵ If you went out on your own, this page is for you. The pages that rank for "Minnesota plumbing license" are DLI's own and exam-prep sites, and they're about getting licensed. This one is about the business: who has to hold what, what the license covers, and what to sort out before the next job.

Minnesota plumbing license types and what each one lets you do

Minnesota licenses the company and the people separately. Your contractor license is the business license, and it "does not of itself qualify its holder to perform the plumbing work" that the personal licenses allow.¹ The people on the job need their own.

Sources for the table: the statute, DLI's license types page and the certification pages.^{1, 2, 6, 7} What counts as plumbing comes from the code: all potable water supply and distribution pipes, all fixtures and traps, all drainage and vent pipes, and the building drains and building sewers within the property lines, including potable water treating equipment.³ I read sections 326B.41 to 326B.49 for a dollar limit or a split between residential and commercial work and found neither.

Your Minnesota plumbing contractor license and the master behind it

Every contractor names a responsible licensed individual, the master plumber who answers for "the performance of all plumbing work" the company does.¹ The rules for that person, from the statute, DLI's page and the certificate the master signs:^{1, 3, 8}

• An owner, officer, member or chief manager of the company, or a managing employee who is "actively engaged in performing plumbing work" for it.
• A managing employee "cannot be employed in any capacity as a plumber for any other contractor," and nobody can be the responsible individual for two companies.
• The master signs a certificate promising to see that each job is done by licensed people or under their supervision, and that permits are filed before the work starts.
• A master who resigns gives the company and DLI 15 days' notice. The company tells DLI within 15 business days of losing its master, then has 60 days to name a new one. Miss that and the license is terminated.

Here's where it bites a new shop. A master who still works as a plumber for another company can't also stand behind a side company of their own. And the master license by itself doesn't let you contract. DLI's 2026 enforcement list has three master plumbers ordered to stop doing plumbing work without a contractor license, in Minneapolis, Madison Lake and Fosston, each with a $5,000 penalty, mostly stayed.⁹

Being someone else's master of record. If another company asks to name you as its responsible individual, you'd be signing for all of its plumbing work, its permits and its unlicensed workers, and if you're not an owner you can't work as a plumber anywhere else. One shop owner on Reddit stated his rate: "$25k a year is what we pay our master of record."¹⁰ Lending your license for someone else's use is listed grounds for DLI to suspend or revoke it, and after a revocation you can't apply again for at least two years.¹¹ We cover the pay and the risk in a separate article.

Registered unlicensed plumbers, apprentices and who can work alone

Everyone doing plumbing for you must be a W-2 employee and either licensed, registered with DLI as a registered unlicensed plumber, or enrolled in a registered apprenticeship.^{3, 12} Registration is $14, gives a "PA" number and renews every June 30 with 2 hours of code training. DLI credits Minnesota experience toward the journeyworker exam (7,000 hours over four years, with set minimums in water distribution, drain, waste and vent, and fixtures) only for time worked while registered, for a licensed contractor, so register a helper on day one.¹²

"Direct supervision" means the licensed plumber is at the location the whole time the unlicensed person is working, physically present and available, and reviews the work before the plumbing is put into use. "Any form of electronic supervision does not meet the requirement." The supervisor must be licensed and employed by the same company, and you keep records of every unlicensed worker's plumbing work for DLI.^{2, 13}

How many helpers per plumber? I found no fixed number in Minnesota's plumbing statutes or DLI's plumbing licensing rules; the direct supervision rule is the limit. For apprentices in a state-registered apprenticeship, the apprenticeship law sets one apprentice for the first journeyworker on the work site plus one for each three more journeyworkers, unless a union agreement or an approved program ratio says otherwise.¹⁴ A licensed journeyworker can work alone and supervise helpers, but works for a contractor; only a master can be the company's responsible individual.

Where your Minnesota plumbing license stops

Plenty of Minnesota shops call themselves "plumbing and heating," so the gas and heating lines matter most here.

• Gas piping and gas appliance hookups. Gas piping isn't in the plumbing license. "A person contracting to do gas, heating, ventilation, cooling, air conditioning, fuel burning, or refrigeration work" must file a $25,000 mechanical contractor bond with DLI; the filing is $100 and lasts two years.¹⁵ By my reading that covers the gas side of a water heater, a range or a generator line, and St. Paul now requires both the plumbing bond and the mechanical bond from every plumbing and gas fitter business it licenses.¹⁷ One of the masters on DLI's 2026 list was also ordered to stop contracting HVAC work without the mechanical bond.⁹
• Heating: boilers, hydronic piping, furnaces. Minnesota has no state heating license, but contracting the work takes the same mechanical bond, and cities license the trade: Minneapolis has steam and hot water systems installer and HVAC licenses, St. Paul steam fitting and warm air licenses.^{15, 16, 17} Hot water heating over 30 psi and 250°F, or steam over 15 psi, is high pressure piping, which needs DLI's high pressure piping license.¹⁸ It cuts the other way too: in October 2026 DLI fined a North Mankato heating and air company $7,000, $5,000 of it stayed, for plumbing work without the license.⁹
• Electric water heaters and other wiring. DLI's bulletin is blunt: "A licensed electrical contractor must be hired to replace the electric water heater." It calls the replacement electrical work that needs electrical licensing and an inspection. Any new wiring, such as a circuit for a sump pump or an electric tankless heater, is electrical work too.¹⁹ The Minnesota electrical license guide covers the electrician's side.
• Water softeners and filters. Inside your license. "Anyone licensed by the Minnesota Department of Labor and Industry (DLI) as a plumber can perform water conditioning work in Minnesota without obtaining a separate water conditioning license."²⁰
• Backflow testing. A separate DLI certificate per person: tester (ASSE 5110) or rebuilder (ASSE 5110 and 5130, plumbers only). Installing, repairing or replacing a reduced pressure zone assembly as a business also takes the plumbing contractor license.^{7, 21}
• Fire sprinklers. A State Fire Marshal fire protection contractor license. A plumbing contractor may make the opening from the potable water piping and may do standpipe and hose systems only; a combined domestic and fire sprinkler system in a house needs the plumbing license plus the Fire Marshal's multipurpose piping certificate.²²
• Septic systems. Design, installation, pumping and service of a septic system need a license from the Minnesota Pollution Control Agency. One combined bond can cover plumbing and septic work.^{1, 23}
• Medical gas. Inside the contractor license, but each plumber doing it needs DLI's medical gas certification (ASSE 6010 and an NITC card, $48).⁷
• Other trades on a remodel. Your plumbing is exempt from residential contractor licensing. Sell drywall, framing or tile on the same contract and two or more of those skills need a residential building contractor or remodeler license.²⁴ The Minnesota residential license guide covers that license.
• Cutting into walls in a pre-1978 home. EPA runs the lead-safe renovation rule (RRP) in Minnesota. Disturbing more than 6 square feet of painted surface in a room, or 20 outside, needs an EPA-certified firm and a certified renovator, sole proprietors included. Penalties run up to $49,772 per violation.²⁵

Minnesota plumbing permits: who pulls them, and the water heater swap

Minnesota's permit rule says whoever intends to "install, enlarge, alter, repair, remove, convert, or replace any gas, mechanical, electrical, plumbing system" must "first make application to the building official and obtain the required permit." Its ordinary repairs exception leaves out any "replacement, or relocation of any standpipe, water supply, sewer, drainage, drain leader, gas, soil, waste, vent or similar piping."²⁶ The statewide rule lists no plumbing work as exempt. Cities do: Minneapolis lets you swap a faucet, toilet, dishwasher or disposal and repair leaking pipes in one- and two-family homes without a permit, as long as you don't alter or replace the supply or piping.²⁷

The water heater swap is the one to get right. Minneapolis lists "Replace or install a water heater" and "Connect gas appliances like stoves, dryers or fireplaces to gas piping" among work that needs a plumbing permit.²⁷ In St. Paul, any work that installs, alters, replaces or changes the waste, vent, water or gas of a plumbing system needs a plumbing permit, and only licensed plumbing and gas fitter contractors and homesteading homeowners may apply.¹⁷ On an electric heater, the electrical contractor files its own Request for Electrical Inspection.¹⁹ Put the permit on the quote as its own line so the customer sees it before you start.

Where DLI is the inspector (state-licensed facilities, public buildings, school projects and areas without a local plumbing inspector), only "a licensed plumbing contractor, licensed water conditioning contractor or authorized license holder performing the work" can apply, before the work starts, and the state fee runs on the value of the plumbing work: $135 up to $1,500, then by steps.²⁸

The homeowner exemption. An owner may do plumbing on the part of a home they own and actually occupy as a residence, "unless otherwise forbidden to do so by a local ordinance."¹ It covers the owner's own hands, not yours: if you do the work, you get the permit.

Who inspects plumbing in Minnesota: your city or DLI

Plumbing is the reverse of electrical. Electrical permits go to the state unless a city has its own inspectors. For plumbing, any city with a water or sewer system may adopt its own plumbing permits and inspections, and nearly every city of any size has.²⁹ I looked up plumbing in DLI's Local Code Lookup on November 3, 2026 for the same 81 cities as our electrical guide, plus 18 small towns:³⁰

Every one of the 81 runs its own plumbing permits and inspections for houses and businesses, Minneapolis, Duluth and Eagan included, though all three leave electrical inspections to the state. The difference is plan review: where a job's plumbing plans need approval, 36 of the 81 review them at city hall and the other 45 have DLI do it.^{30, 31} DLI inspects the projects it keeps for itself: hospitals, nursing homes and other state-licensed facilities, state buildings, school district and charter school projects, and "projects of a special nature" such as dialysis clinics.³¹ In places that haven't adopted the State Building Code, like the four small towns in the table and many rural townships, DLI's pages disagree about houses: its inspections page lists "All other building types in non-code enforced areas" as DLI's, while its FAQ names only public, commercial, industrial and licensed buildings there.³¹ Before the first job in a township with no building department, call DLI's plumbing line, 651-284-5063, and ask who inspects.

The plumbing code applies statewide either way.^{32, 33} New plumbing, and any part of an existing system you alter, must be inspected and tested, and DLI asks you to tell the inspector at least eight hours before the work is ready.³¹ A city can't revoke, suspend or restrict your state license.³³

Minneapolis and St. Paul license plumbers too

State law stops cities from barring state-licensed plumbing contractors, with one old exception: cities that already licensed plumbers by ordinance before April 21, 1933. It also says cities can't make you post their own bond or carry extra liability insurance to do plumbing.²⁹ Minneapolis and St. Paul both run their own plumbing licenses, and St. Paul's application asks for more insurance than the state minimum anyway. I can't square that with the statute, but the city won't issue the license without it.

• Minneapolis: "Plumbers working in Minneapolis need a license." The city's plumbing license covers drains, sewers and water pipes, and also fuel gas piping and venting, gas burner equipment, and power burners up to 100,000 BTU. It takes a surety bond on the state's $25,000 bond form and a city competency card where required. The city also has a gas fitter license for gas burning equipment and a steam and hot water systems installer license for heating piping.¹⁶ Start at the city's trade licenses page.
• St. Paul: a Plumbing/Gasfitter Business Trade License, $188 a year, expiring every December 1. It needs a St. Paul master plumbing and gas fitter certificate of competency (a city exam), liability insurance of $500,000 combined single limit (or $500,000 bodily injury and $200,000 property damage) naming the city as certificate holder, and both the $25,000 plumbing bond and the $25,000 mechanical bond on file with DLI. Every trade worker on a St. Paul job registers with the city each year, from $37.¹⁷ Start at the city's trade licensing page.

I checked those two cities' licensing pages. Other cities may run older local rules too, so ask the building department before your first job in a new town.

Backflow and the water utility

The code lets a testable backflow assembly be installed only where someone runs a testing program, with tests at least once a year.³² Cities and water utilities run those programs, each with its own rules. Minneapolis is a good example of what to expect: a plumbing permit to install, replace, relocate or remove a regulated backflow assembly; the plumbing contractor registers the change online when the work is done; tests at installation and every year after, submitted through The Compliance Engine by a Minnesota-certified tester; $18 per test, and a $500 penalty for non-compliance.³⁴ Before your first backflow job in a new water district, call the utility and ask how it takes test results. The Minneapolis program page lists the steps.

Can I take this job? A table for Minnesota plumbing contractors

Your first 30 days: the checklist

The same list as the printable sheet. Week 1 is the license and paperwork; the rest can run alongside your first jobs.

A. License, company and the master

• Look up the company license and the master's license in DLI's license lookup and write down both expiry dates.^{3, 12}
• Check your Secretary of State filing is active and the name matches exactly on the license, bond, insurance certificate, trucks and ads. An LLC is $155 to file online; an assumed name, if you trade under another name, is $50 online.^{35, 36} Changing from sole proprietor to LLC later means a new contractor license.³⁶
• Confirm the master's role: owner, officer, member or chief manager, or a W-2 managing employee who works as a plumber for nobody else. One company only.¹
• Write down a plan B for the master: 15 business days to tell DLI, 60 days to replace.¹

B. Bonds, insurance, workers' comp, people

• $25,000 plumbing contractor bond on DLI's form. It's continuous, and it pays out up to $25,000 in each two-year period.⁴
• Liability covering premises, operations, products and completed operations: at least $50,000 per person, $100,000 per occurrence and $10,000 property damage, from a Minnesota-licensed insurer, on an agent-signed certificate naming DLI as certificate holder.^{1, 3}
• Gas or heating work: file the $25,000 mechanical contractor bond ($100 for two years) before you contract any.¹⁵
• Workers' comp in place before the first employee starts, and DLI's Certificate of Compliance form up to date. Without it, DLI can order up to $1,000 per employee per week, and false information on the form is a $2,000 penalty.³⁷
• Every worker licensed or registered (PA number), on W-2, and directly supervised; keep the records.^{12, 13}
• A Minnesota Tax ID from the Department of Revenue before you withhold Minnesota income tax from the first paycheck.³⁸

C. Permits and inspections

• Look up every city you work in: who inspects plumbing, and the inspector's phone.³⁰
• Shop rule: the permit goes in before the work starts, water heater swaps included.^{8, 26}
• For public or state-licensed buildings where DLI inspects: an account in DLI's online permit system.²⁸
• Put the permit on the quote as its own line.

D. City licenses and the water utility

• Minneapolis: the city plumbing license (and gas fitter or steam and hot water licenses if you do that work).¹⁶
• St. Paul: the Plumbing/Gasfitter Business Trade License, the city master certificate of competency, $500,000 insurance, both bonds, and trade worker registration for each worker.¹⁷
• Backflow: the DLI tester or rebuilder certificate for whoever tests, and an account with each utility's reporting system (Minneapolis uses The Compliance Engine).^{21, 34}

E. Name, number and contracts

• Every vehicle used on plumbing work: company name and license number exactly as on the license, contrasting color, characters at least 3 inches high and 1/2 inch wide, on both sides.¹
• License number on quotes, contracts, invoices and your website. I found no plumbing rule that demands it there, but customers look it up. Our plumbing invoice template has a line for it.
• A residential contract with the scope and price in writing, the mechanic's lien notice (required if you buy materials or hire subs for the job, or you lose the lien), and the statutory warranty, which is 2 years for plumbing work on a home improvement.³⁹ The Minnesota residential construction contract template has the exact wording.
• Your subs lined up: a licensed electrical contractor (electric water heaters, new circuits), a fire protection contractor, an MPCA-licensed septic company, and a bonded mechanical contractor if you won't file the mechanical bond yourself.^{15, 19, 22, 23}
• Pre-1978 homes: EPA RRP firm certification and a certified renovator if you'll open painted walls.²⁵

F. Renewals and continuing education

• Contractor license: December 31 of odd-numbered years, $188, $90 late.³⁶
• Master license: December 31 of even-numbered years, $93, $40 late. Journeyworkers: December 31 of odd-numbered years, $53, $20 late. Both need 16 hours of approved continuing education per two-year period, at least 8 on the State Plumbing Code.^{12, 40}
• Registered unlicensed plumbers: every June 30, 2 hours of code training.¹²
• Backflow certificates every two years with current ASSE certification; the mechanical bond filing every two years; St. Paul's trade license every December 1.^{15, 17, 21}
• Insurance, workers' comp and bond renewal dates in the calendar, with the new certificate sent to DLI each time.³⁶

What happens if you cross the line

• Plumbing without the contractor license. DLI can fine up to $10,000 per violation, issue a stop work order with $5,000 a day for working through it, and it's a misdemeanor (up to 90 days and $1,000).^{11, 41} This happens. DLI's 2026 plumbing list so far has 39 orders, by my count, telling a company or person to stop plumbing work without the license, mostly handymen and remodelers, with penalties mostly $5,000 to $10,000 and part usually stayed. Three went to master plumbers working without a contractor license, $5,000 each.⁹
• Gas or heating work without the mechanical bond. The same penalty powers apply. One master plumber's 2026 order covered both.^{9, 11}
• No permit. The permit rule is part of the State Building Code, which counts as "applicable law" for the DLI penalties above, and your master signed a certificate promising permits go in before work starts.^{8, 26, 43} On top of that, each city sets its own fees and orders for work done without a permit; I found no statewide schedule for plumbing.
• Lending the license, or a master in name only. Grounds to suspend or revoke it, with at least two years before you can apply again.¹¹
• No workers' comp. Up to $1,000 per employee per week, and a willful failure is a gross misdemeanor.³⁷
• Getting paid. I found nothing in Minnesota's plumbing statutes that voids an unlicensed plumber's contract or takes away the mechanic's lien; the lien rule for unlicensed contractors in 326B.845 is written for the residential building licenses.⁴² I didn't research Minnesota case law, so don't count on collecting for unlicensed work; ask a lawyer.
• Insurance. I found no Minnesota rule on whether a liability policy pays for work outside your license. Your insurer must tell DLI if it cancels the policy, and the license needs a policy in force.¹ Ask your agent in writing what the policy excludes, gas work in particular.

More for new plumbing contractors

• How much to charge per hour: service call minimum, first hour and flat prices, with a free rate sheet.
• Water heater replacement checklist: the code items, the permit and what to charge, with a free printable.
• You got your master plumber license. Now what? Stay for a raise or start your own plumbing business, with the numbers for each.
• Asked to be the master of record: what being a company's plumbing qualifier pays, and what it can cost you.

Where Deepsel fits

Deepsel won't pull your plumbing permit, book the inspector, file backflow test results with the utility or remind you when the license, bonds or insurance renew. Here's what it does do. You write one shop-wide terms text that's copied onto every quote the customer sees and signs on screen, and one invoice footer that goes on every invoice: put the company name as licensed, the license number and your warranty line there once. Each job has internal notes and internal file attachments that customers never see, which is a place for the permit number, the inspection report and a backflow test report, and each visit holds photos. Checklist templates you build (a water heater swap list with the permit, the expansion tank and the gas bond check, say) can be added to a quote and ticked off by the office and the techs. A customer's equipment record holds the water heater's type, brand, model, serial number, year, fuel, gallons, venting and a nameplate photo. The Free plan covers 30 estimates and 30 invoices a month for your whole team; Pro is $29 a month for unlimited estimates and invoices. Details are on the pricing page.

Frequently asked questions

Do you need a license to do plumbing in Minnesota?

Yes. Any person or company that performs or offers to perform plumbing work, paid or not, needs a plumbing contractor license from the Department of Labor and Industry (DLI), and every person doing the work must be a licensed master or journeyworker plumber, a registered unlicensed plumber working under direct supervision, or an apprentice in a registered program. A master plumber license alone doesn't let you contract: the company needs its own contractor license with a master named as its responsible licensed individual. Two exceptions matter to contractors: a homeowner may do plumbing on the home they own and live in, unless a local ordinance forbids it, and a general contractor who subs all plumbing to a licensed plumbing contractor doesn't need a plumbing license itself.

Can I do my own plumbing in Minnesota?

If you own the home and live in it, yes, unless your city forbids it by ordinance. The exemption covers plumbing work on the part of the premises the owner actually occupies as a residence, and the work still has to meet the Minnesota Plumbing Code and get a permit where the city requires one. St. Paul, for one, lets only licensed plumbing and gas fitter contractors and homesteading homeowners apply for plumbing permits. A rental the owner doesn't live in doesn't qualify, and the exemption covers the owner's own hands: a contractor can't work under it.

What does a Minnesota plumbing contractor license allow?

Plumbing work anywhere in Minnesota, residential or commercial, of any size, through licensed and registered people the company employs. There is no dollar limit. Plumbing here means the water supply and distribution piping, fixtures and traps, drain, waste and vent piping, and building drains and sewers within the property lines, plus potable water treating equipment such as softeners. It doesn't cover contracting gas or heating work (that needs the $25,000 mechanical contractor bond), the electrical side of an electric water heater (a licensed electrical contractor), fire sprinkler systems (State Fire Marshal license) or septic systems (Minnesota Pollution Control Agency license).

What is a restricted plumbing license in Minnesota?

A restricted master or restricted journeyworker plumber license lets the holder work only in cities and towns of 5,000 people or fewer by the last federal census. A restricted plumbing contractor is a company whose responsible individual holds a restricted master license, and it can't contract work in places over 5,000. These licenses were granted only on applications filed before October 1, 2008 or between October 1 and 15, 2009, and a restricted license not renewed within 12 months of expiring is lost for good. A new plumber can't get one today; the route is the journeyworker and master exams.

How much is a Minnesota plumbing contractor license and when does it expire?

The application and renewal fee is $188, plus a $90 late fee if the renewal arrives after the license expires. Plumbing contractor licenses expire on December 31 of odd-numbered years. Master plumber licenses expire on December 31 of even-numbered years under the statute and DLI's rule, with a $93 renewal ($40 late), and journeyworker licenses on December 31 of odd-numbered years with a $53 renewal ($20 late). Both personal licenses need 16 hours of approved continuing education per two-year period, at least 8 of them on the State Plumbing Code.

What insurance and bond does a Minnesota plumbing contractor need?

A $25,000 surety bond on DLI's Plumbing Contractor Surety Bond form, and public liability insurance including products liability with limits of at least $50,000 per person and $100,000 per occurrence, plus property damage insurance of at least $10,000. DLI's page adds that the policy must cover premises, operations, products and completed operations, the certificate must be signed by a licensed agent with DLI as certificate holder, and the insurer must be licensed in Minnesota. Workers' compensation is required once you have an employee. To contract gas or heating work you also file the $25,000 mechanical contractor bond, $100 for two years.

Do I need a permit to replace a water heater in Minnesota?

In most cities, yes. Minnesota's permit rule requires a permit to install, alter, repair or replace any plumbing system or gas equipment the code regulates, and its ordinary repairs exception excludes replacing water, drain, gas or vent piping. Minneapolis lists replacing or installing a water heater, and connecting gas appliances, among the work that needs a plumbing permit. Rules and fees are the city's, so check before the first swap in each town. On an electric water heater, DLI says the plumber must hire a licensed electrical contractor, because replacing it counts as electrical work with its own permit and inspection.

What plumbing code does Minnesota use?

The 2020 Minnesota Plumbing Code, Minnesota Rules chapter 4714, in effect since December 17, 2021. It adopts the 2018 Uniform Plumbing Code with Minnesota amendments, applies statewide to new work, additions, alterations, repairs and replacements, and is published by IAPMO as one Minnesota code book that also includes the licensing rules (chapter 4716) and the administration code (chapter 1300). DLI links a free online copy.

Do I need a water conditioning license if I'm a licensed plumber?

No. DLI says anyone it licenses as a plumber can do water conditioning work without a separate water conditioning license, and the statute exempts licensed master and journeyworker plumbers from the water conditioning licensing sections. The separate water conditioning contractor, master and journeyworker licenses are for companies and people who install and service softeners and filters without a plumbing license. Water heaters are not water conditioning: installing one is plumbing work.

How do I get backflow certification in Minnesota?

Pass an ASSE course and get the matching DLI certificate. A backflow prevention tester (BT) needs current ASSE 5110 certification and may only test reduced pressure zone assemblies; it doesn't need a plumber license. A backflow prevention rebuilder (BF) must hold a plumbing license plus current ASSE 5110 and 5130 certification and may install, test, repair and rebuild them. Certificates run two years. Installing, repairing or replacing an RPZ as a business also needs the plumbing contractor license. Some cities run their own test reporting: Minneapolis takes results online and charges $18 per test.

Sources

1. Minnesota Statutes 326B.46, Licensing, bond and insurance (2026 edition): subd. 1(a) (master, journeyworker and restricted licenses; owner-occupant may do plumbing "on premises or that part of premises owned and actually occupied by the worker as a residence, unless otherwise forbidden to do so by a local ordinance"), 1(b) (a master "who shall be responsible for proper installation, is in charge"), 1(c) ("no person shall perform or offer to perform plumbing work with or without compensation unless the person obtains a contractor's license. A contractor's license does not of itself qualify its holder to perform the plumbing work"), subd. 1a (exemptions), subd. 1b (responsible licensed individual "responsible for the performance of all plumbing work"; plumbing contractor license "authorizes the contractor to offer to perform and, through licensed and registered individuals, to perform plumbing work in all areas of the state"; restricted contractor excluded from "cities and towns with a population of more than 5,000"; owner, partner, chief manager, officer or managing employee; a managing employee "cannot be employed in any capacity as a plumber for any other contractor. An individual may be the responsible licensed individual for only one contractor"; notify "within 15 business days"; "60 days from the departure ... to obtain a new responsible licensed individual"), subd. 2 ($25,000 bond for plumbing work, or plumbing and septic work; liability "including products liability insurance with limits of at least $50,000 per person and $100,000 per occurrence and property damage insurance with limits of at least $10,000"; Minnesota-licensed insurer; insurer notifies the commissioner of cancellation), subd. 7 (vehicles: "the contractor's name and license number as it appears on the contractor's license in contrasting color with characters at least three inches high and one-half inch in width affixed to each side of the vehicle"). revisor.mn.gov, read November 3, 2026.
2. Minnesota Statutes 326B.42, Definitions: subd. 2 (direct supervision: the supervising plumber "is present at the location", "physically present and immediately available", "any form of electronic supervision does not meet the requirement of physically present", reviews the work "before the plumbing is operated"), subd. 3 and 4 (journeyworker and master plumber), subd. 8 to 10 (plumbing contractor, responsible individual, restricted plumbing contractor). revisor.mn.gov, read November 3, 2026.
3. Minnesota Department of Labor and Industry, "Plumbing contractor licensing basics": plumbing systems include "all potable water, building supply, and distribution pipes; all plumbing fixtures and traps; all drainage and vent pipes; and all building drains and building sewers ... within the property lines of the premises and includes potable water piping, potable water treating or using equipment"; responsible licensed individual must "Hold an active master plumber license" and be "an owner, officer, or member ... or a W-2 employee who is actively engaged in the company's plumbing work and cannot be employed as a plumber by any other contractor"; "Not be the responsible licensed individual for any other plumbing contractor"; policy must cover "premises, operations and products, and completed operations"; "limits of at least $50,000 per person and $100,000 per occurrence and property damage insurance with limits of at least $10,000"; "Provide a $25,000 surety bond"; "The initial license application and license renewal fee is $188"; "Make sure your company's license number appears on all company vehicles"; "Plumbing contractor licenses expire on December 31 of odd-numbered years"; "General contractors and construction management firms that contract with licensed subcontractors to perform plumbing work are not required to have their own plumbing contractor license." dli.mn.gov, read November 3, 2026.
4. DLI, Plumbing Contractor Surety Bond form (version 6.20.2024): penal sum "TWENTY-FIVE THOUSAND DOLLARS ($25,000.00)"; the surety's liability "shall in no event exceed the amount set forth above for each two-year period the bond remains in force"; "it is the intention of the parties that this bond be continuous"; "Principal shall not conduct work or contract to conduct work requiring licensure until the State of Minnesota has issued the license", dli.mn.gov (PDF); DLI, Certificate of Insurance, plumbing and pipelayer ("limits of at least $50,000 per person and $100,000 per occurrence and property damage insurance with limits of at least $10,000"), dli.mn.gov (PDF); both read November 3, 2026.
5. Reddit comment, October 11, 2025: "I just got my master license and im trying to figure out if i can get a raise at my company or try to go on my own, super stressful." State not given. reddit.com, quoted as checked in Deepsel's plumbing research, November 2, 2026.
6. DLI, "Plumbing license types and credentials": master plumber license "authorizes the individual to perform plumbing statewide, for both interior plumbing and exterior water service, sanitary sewer and storm sewer systems within the property lines"; restricted master and journeyworker limited to "cities and towns with a population of fewer than 5,000"; registered unlicensed individual; pipe layer bond and pipelayer card ("not inside of buildings"); water conditioning contractor and installer. dli.mn.gov, read November 3, 2026.
7. DLI, "Backflow prevention certification" (tester: ASSE 5110, "A plumber license is not required"; rebuilder: "must also hold a current plumbing license", ASSE 5130 and 5110), dli.mn.gov; DLI, "Medical gas certification" ("A contractor offering to perform or performing medical gas installations, maintenance or repair must be licensed by our agency as a plumbing contractor"; ASSE 6010, NFPA 99C brazing, NITC card; "The initial registration fee is $48"), dli.mn.gov; Minnesota Statutes 326B.475 (restricted licenses: applications "between October 1, 2009, and October 15, 2009" and before October 1, 2008; work "in all areas of the state except in cities and towns with a population of more than 5,000"; "failure to renew ... within 12 months after the expiration date will result in permanent forfeiture"), revisor.mn.gov; all read November 3, 2026.
8. DLI, Certificate of Responsible Individual (master plumber or restricted master plumber): the master is responsible for "ensuring that, when required, each job will be done by licensed employees, or under the on-the-job supervision of properly licensed employees" and "ensuring that permits or inspection forms are filed with the applicable inspection jurisdiction before the commencement of plumbing work"; "notifying the department 15 days in advance of resigning"; a managing employee "may not perform plumbing work for any other employer". dli.mn.gov (PDF), read November 3, 2026.
9. DLI, "Plumbing Enforcement Actions, 2026 Year to Date": orders to "cease and desist from performing or offering to perform plumbing work in the state of Minnesota without the requisite licensure" (39 such orders by my count, most also covering residential or electrical work; penalties mostly $5,000 to $10,000, usually partly stayed); master plumbers ordered to stop plumbing work "without the requisite plumbing contractor license" (Minneapolis, February 10, 2026, "$5,000 monetary penalty, $4,500 stayed with conditions"), "without the requisite contractor license" (Fosston, June 22, 2026, "$5,000 monetary penalty, stayed with conditions") and without licensure plus "contracting to perform mechanical/HVAC work in the state of Minnesota without the requisite mechanical contractor bond" (Madison Lake, March 30, 2026, "$5,000 monetary penalty, stayed with conditions"); a North Mankato heating and air conditioning company ordered to stop plumbing work without licensure, "$7,000 monetary penalty, $5,000 stayed with conditions" (October 21, 2026). dli.mn.gov (PDF), read November 3, 2026.
10. r/Plumbing comment, February 23, 2026: "$25k a year is what we pay our master of record." reddit.com, quoted as checked in Deepsel's plumbing research, November 2, 2026.
11. Minnesota Statutes 326B.082: subd. 7 ("a monetary penalty of up to $10,000 for each violation of applicable law"), subd. 10 ("a civil penalty of $5,000 per day against a person for each day the person conducts business operations that are in violation of a stop work order"), subd. 11(b)(4) (sanctions where a person "allowed the alteration or use of the person's own permit, license, registration, or certificate by another person") and (d) (no reapplication "for at least two years"), subd. 16 ("a person who violates an applicable law is guilty of a misdemeanor"). revisor.mn.gov, read November 3, 2026.
12. DLI, "Plumbing license basics" (workers: who can do plumbing work; registered unlicensed plumber "Pay the $14 initial application fee", "PA" number, "Unlicensed plumber registrations expire June 30 each year", two hours of continuing education; journeyworker and master exams, $50 exam fee; "Complete 16 hours of DLI-approved continuing education (at least eight hours must relate to the State Plumbing Code)"; "The journeyworker renewal fee is $53 (late fee of $20 added for late renewals)"; "The master plumber renewal fee is $93 (late fee of $40 added for late renewals)"), dli.mn.gov; DLI, "Registered unlicensed plumbers" (7,000 hours over four years, with 2,000 hours of water distribution, 2,000 of drain, waste and vent and 1,000 of fixture installation; "must also be a W-2 employee of a licensed plumbing contractor"), dli.mn.gov; DLI license and registration lookup, dli.mn.gov; all read November 3, 2026.
13. Minnesota Statutes 326B.47 subd. 1 (registration; apprentices and registered unlicensed individuals assist "only while under the direct supervision" of a licensed plumber "employed by the same employer"; contractors "shall maintain records" of them for the department) and subd. 2 (four years of practical experience for the journeyworker exam). revisor.mn.gov, read November 3, 2026. I also read Minnesota Rules chapter 4716 for a supervision ratio and found none.
14. Minnesota Statutes 178.036 subd. 5 (absent a collective bargaining agreement, "for occupations in the building and construction trades ... one apprentice for the first journeyworker employed at the work site plus one apprentice for each additional three journeyworkers employed at the work site", or the majority ratio in the trade, or a program ratio approved by the Apprenticeship Advisory Board). revisor.mn.gov, read November 3, 2026.
15. Minnesota Statutes 326B.197 ("A person contracting to do gas, heating, ventilation, cooling, air conditioning, fuel burning, or refrigeration work must give and maintain bond to the state in the amount of $25,000"), revisor.mn.gov; DLI, "Mechanical contractor bond requirements" ("businesses must file a $25,000 mechanical contractor bond with DLI in order to contract to perform gas, heating, ventilation, cooling, air conditioning, fuel burning or refrigeration work"; "The fee for filing a bond with DLI is $100 and the filing is valid for two years"; "mechanical contractors must comply with local licensing requirements"), dli.mn.gov; both read November 3, 2026.
16. City of Minneapolis, "Trade licenses" (gas fitter, HVAC Class A or B, oil burner installer, plumbing, steam and hot water systems installer), "Plumbing license" ("Plumbers working in Minneapolis need a license"; work includes "Fuel gas piping and venting", "Gas burner equipment" and "Power burners that do not exceed one hundred thousand (100,000) BTUs"; surety bond on the "State of Minnesota $25,000 bond form"; competency card), "Gas fitter license" and "Steam and hot water systems installer license" (pages last updated September 3, 2026). minneapolismn.gov, read November 3, 2026.
17. City of Saint Paul, "Plumbing/Gasfitter Business Trade License" (it covers drainage, water, gas and other piping, fixtures, water heaters, and to "clean drains, remove obstructions"; requires "A current City of Saint Paul Certificate of Competency (Master Plumbing/Gasfitter)", insurance "with a combined single limit of liability for bodily injury and property damage of $500,000; or $500,000 bodily injury and $200,000 property damage"; "Both a $25,000 Plumbing Contractor Bond (PC) AND a $25,000 Mechanical Bond (MB) are now required to be filed with the Minnesota Department of Labor and Industry"; "The annual fee for trade licenses is $188.00 each"; "All Trade Licenses expire on December 1"), stpaul.gov; "Business Trade License, Competency Cards, and Trade Worker Registration" (steam fitting and warm air trade licenses; "Every trade worker who works on any building or structure in Saint Paul must be currently registered"; $37 for the first tier), stpaul.gov; "Plumbing/Gas Permits & Inspections" (a plumbing permit to "install new, alter, replace, repair, relocate, reinstall, or change the waste and/or vent, water, or gas for a plumbing system"; "Licensed Plumbing/Gas Fitter Contractors and Homesteading Homeowners can apply"; separate sewer permits), stpaul.gov; all read November 3, 2026.
18. Minnesota Statutes 326B.91 subd. 4 ("High pressure piping" includes "any systems of piping hot water or other medium used for heating that exceed 30 p.s.i. gauge and 250 degrees Fahrenheit, or any system of high pressure steam") and subd. 5 (high pressure steam: "in excess of 15 pounds per square inch"). revisor.mn.gov, read November 3, 2026.
19. DLI bulletin, "Clarification about electrical licensing requirements when replacing HVAC equipment and water heaters" (revised December 30, 2024): "Does a licensed plumber or HVAC contractor have to hire a licensed electrical contractor to replace an electric water heater? A) Yes. A licensed electrical contractor must be hired to replace the electric water heater. ... State law defines replacing an electric water heater as 'electrical work' and requires electrical licensing and inspections", dli.mn.gov (PDF); Minnesota Statutes 326B.38 subd. 2 ("The installation of electrical wiring to an electrical appliance unit is covered"), revisor.mn.gov; both read November 3, 2026.
20. DLI, "Water conditioning license basics" ("Anyone licensed by the Minnesota Department of Labor and Industry (DLI) as a plumber can perform water conditioning work in Minnesota without obtaining a separate water conditioning license"), dli.mn.gov; Minnesota Statutes 326B.55 (water conditioning contractor license), 326B.56 ($3,000 water conditioning bond), 326B.57 ("The installation of water heaters shall not constitute water conditioning installation"), 326B.59 (the licensing provisions "do not apply to master plumbers and journeyworker plumbers"), revisor.mn.gov; all read November 3, 2026.
21. Minnesota Statutes 326B.437 ("No person shall perform or offer to perform the installation, maintenance, repair, replacement, or rebuilding of reduced pressure zone backflow prevention assemblies unless the person obtains a plumbing contractor's license"; testing only with a rebuilder or tester certificate; certificates "issued for an initial period of two years and must be renewed every two years"), revisor.mn.gov; DLI, "Continuing education requirements for plumbers" (testers and rebuilders "must have a current ASSE tester 5110 and/or repairer 5130 certification"), dli.mn.gov; both read November 3, 2026.
22. Minnesota Statutes 299M.01 subd. 7 ("Openings from potable water piping for fire protection systems must be made by persons properly licensed under section 326B.46. Persons properly licensed under section 326B.46 may also sell, design, install, modify or inspect a standpipe, hose system only") and subd. 8b (multipurpose potable water piping systems: licensed under 326B.46 "and is certified pursuant to section 299M.03"); 299M.03 subd. 1 (fire protection contractor license). revisor.mn.gov and revisor.mn.gov, read November 3, 2026.
23. Minnesota Statutes 115.56 subd. 2 ("a person may not design, install, maintain, pump, inspect, or provide service to a subsurface sewage treatment system without a license"; the $25,000 bond "may be for both plumbing work and subsurface sewage treatment work"), revisor.mn.gov; DLI, "Pipe layer bond" ("Contractors who install subsurface sewage treatment systems (SSTS) are licensed by the Minnesota Pollution Control Agency"), dli.mn.gov; both read November 3, 2026.
24. Minnesota Statutes 326B.805 subd. 6 (exempt from residential licensing: "a plumber, electrician, or other person whose profession is otherwise subject to statewide licensing, when engaged in the activity which is the subject of that licensure") and 326B.802 subd. 15 (the special skills). revisor.mn.gov, read November 3, 2026 (from Deepsel's Minnesota residential license research).
25. U.S. EPA, "Lead Renovation, Repair and Painting Program" (Minnesota is not an authorized state; firm certification applies to "all firms, even sole proprietorships"), epa.gov; 40 CFR 745.83 (minor repair and maintenance: under 6 square feet per room inside, 20 square feet outside), law.cornell.edu; 40 CFR 19.4, Table 1 (TSCA penalty $49,772 per violation), law.cornell.edu; all read November 3, 2026 (from Deepsel's Minnesota license research).
26. Minnesota Rules 1300.0120, Permits: subp. 1 (an owner or authorized agent who intends to "erect, install, enlarge, alter, repair, remove, convert, or replace any gas, mechanical, electrical, plumbing system ... shall first make application to the building official and obtain the required permit"), subp. 4 (exemptions listed for building, gas, mechanical and electrical work only), subp. 6 (ordinary repairs do not include "addition to, alteration of, replacement, or relocation of any standpipe, water supply, sewer, drainage, drain leader, gas, soil, waste, vent or similar piping"). revisor.mn.gov, read November 3, 2026.
27. City of Minneapolis, "Plumbing permits" (permit needed to "Replace or install fixtures", "Replace or install water piping", "Replace or install a water heater", "Install a non-testable backflow preventer device", "Connect gas appliances like stoves, dryers or fireplaces to gas piping"; last updated June 30, 2026), minneapolismn.gov; "Construction work exempt from permit" (one- and two-family dwellings, if "You do not alter or replace the existing water supply line or plumbing piping system": replace sink faucets and water closets, dishwashers and garbage disposals, internal parts; repair leaking fixtures and pipes; last updated March 31, 2026), minneapolismn.gov; both read November 3, 2026.
28. DLI, "Apply for a plumbing inspection permit" ("All inspection permits must be applied for by a licensed plumbing contractor, licensed water conditioning contractor or authorized license holder performing the work"), dli.mn.gov; DLI, "Plumbing permits and inspection fees", dli.mn.gov; Minnesota Statutes 326B.49 subd. 3 (permit applied for "Before commencement of a plumbing installation to be inspected by the commissioner"; "$0 to $1,500, $135"), revisor.mn.gov; all read November 3, 2026.
29. Minnesota Statutes 326B.44, Local regulations (any city "having a system of waterworks or sewerage, regardless of population" may adopt plumbing permits and inspections; no such entity "shall prohibit plumbing contractors licensed by the commissioner from engaging in or working at the business of plumbing, except cities and statutory cities which, prior to April 21, 1933, by ordinance required the licensing of plumbers"; no added bond or public liability insurance "as a prerequisite for engaging in the business of plumbing"). revisor.mn.gov, read November 3, 2026.
30. DLI, Local Code Lookup (Minnesota State Building Code Jurisdiction Directory), plumbing fields "MUNICIPALITY INSPECTS NON-STATE PROJECTS" and "MUNICIPALITY INSPECTOR NAME", queried city by city on November 3, 2026; electrical authority for the same cities from the same directory, queried the same day for our Minnesota electrical license guide. workplace.doli.state.mn.us.
31. DLI, "Plumbing inspections" ("New plumbing systems and parts of existing systems that have been altered must be inspected and tested"; "The plumbing contractor should notify the proper administrative authority at least eight hours before the work is to be inspected or tested"; DLI inspects "All other building types in non-code enforced areas of the state"; general questions 651-284-5063), dli.mn.gov; DLI, "Plumbing Inspection FAQs" (DLI "performs required inspections of public buildings, including commercial, industrial and licensed facilities, in areas that have not adopted the State Building Code"), dli.mn.gov; DLI, "Plumbing plan review agreements as of Oct. 13, 2026", dli.mn.gov (PDF); all read November 3, 2026.
32. DLI, "2020 Minnesota Plumbing Code" (chapter 4714 "took effect Dec. 17, 2021", "incorporates by reference the 2018 edition of the Uniform Plumbing Code with Minnesota amendments"; regulates plumbing "statewide for all buildings including new, addition, alteration, repair and replacement"), dli.mn.gov; Minnesota Rules chapter 4714, section 603.5.23.2 (a testable backflow assembly "is permitted only when a periodic testing and inspection program ... is provided"; "Inspection intervals shall not exceed one year"), revisor.mn.gov; both read November 3, 2026.
33. Minnesota Statutes 326B.43 subd. 1 (uniform minimum standards "effective for all new plumbing installations performed anywhere in the state") and subd. 2(p) ("no municipality shall revoke, suspend, or place restrictions on any plumbing license issued by the state"). revisor.mn.gov, read November 3, 2026.
34. City of Minneapolis, "Regulated backflow assembly and testing" (plumbing permit when a device is installed, replaced, relocated or removed; "The plumbing contractor must register the change using the online form"; tested "when first installed and at least annually thereafter", results through The Compliance Engine by "a MN-state certified backflow tester"; "$18 per test", "$500 non-compliance penalty"; last updated October 1, 2026). minneapolismn.gov, read November 3, 2026.
35. Minnesota Secretary of State, "Business Filing and Certification Fee Schedule": LLC articles of organization $155 online; certificate of assumed name $50 online. sos.mn.gov, read November 3, 2026 (from Deepsel's Minnesota electrical license research).
36. DLI, "Plumbing contractor license renewal": "Plumbing contractor licenses expire on Dec. 31 in odd-numbered years"; "your business name must appear EXACTLY as it is filed with the Secretary of State"; a change of business structure means "you will need to apply for a new license"; "the renewal fee is $188. A $90 late fee is added"; bonds are continuous. dli.mn.gov, read November 3, 2026.
37. DLI, "Certificate of Compliance, Minnesota Workers' Compensation Law" (Minn. Stat. 176.182 withholds licenses without evidence of coverage; missing or false information "shall result in a $2,000 penalty"), dli.mn.gov (PDF); Minnesota Statutes 176.181 subd. 2 to 4 (every employer must insure; "a penalty of up to $1,000 per employee per week"; willful failure "is guilty of a gross misdemeanor"), revisor.mn.gov; both read November 3, 2026.
38. Minnesota Department of Revenue, "Minnesota Tax ID Requirements": a Minnesota Tax ID is needed to "Withhold Minnesota Income taxes from employees' wages". revenue.state.mn.us, read November 3, 2026 (from Deepsel's Minnesota electrical license research).
39. Minnesota Statutes 514.011 subd. 1 (anyone contracting with the owner who "has contracted or will contract with any subcontractors or material suppliers" includes the prescribed notice in the written contract; "A person who fails to provide the notice shall not have the lien"), revisor.mn.gov; 327A.02 subd. 3(b) ("home improvement work involving the installation of plumbing, electrical, heating or cooling systems": two years), revisor.mn.gov; both read November 3, 2026 (from Deepsel's Minnesota contract research).
40. Minnesota Statutes 326B.49 subd. 1(b) and (c) ("All journeyworker plumber's licenses shall expire on December 31 of each odd-numbered year"; "All master plumber's licenses shall expire on December 31 of each even-numbered year"; "All contractor licenses shall expire on December 31 of each odd-numbered year"), revisor.mn.gov; Minnesota Rules 4716.0040 (same dates), revisor.mn.gov; DLI, "Continuing education requirements for plumbers" (16 hours per two-year license period, "At least eight hours must pertain to the State Plumbing Code"), dli.mn.gov; all read November 3, 2026.
41. Minnesota Statutes 609.02 subd. 3 and 609.03: a misdemeanor carries "not more than 90 days or ... a fine of not more than $1,000". revisor.mn.gov, read November 3, 2026 (from Deepsel's Minnesota license research).
42. Minnesota Statutes 326B.845 subd. 2: "An unlicensed person who knowingly violates sections 326B.802 to 326B.885 has no right to claim a lien under section 514.01 and the lien is void." Those sections are the residential building contractor licensing law, not the plumbing law (326B.41 to 326B.49). revisor.mn.gov, read November 3, 2026 (from Deepsel's Minnesota license research).
43. Minnesota Statutes 326B.081 subd. 3: "Applicable law" means the provisions of listed sections, "this chapter", and "all rules, orders, stipulation agreements, settlements, compliance agreements, licenses, registrations, certificates, and permits adopted, issued, or enforced by the department" under them. revisor.mn.gov, read November 3, 2026.