image features a water filter laying on a kitchen counter. blog post covers the information you need to get the C55 license for water conditioning contractors

C-55 License: Water Conditioning

Table of Contents

Water Conditioning Contractors specialize in: 

  • Water Analysis
  • Installation
  • Repair and Maintenance

of various water purification or conditioning systems. 

  • As society becomes more and more conscious of the harmful chemicals that are in our water.
  • Contractors specializing in water conditioning will have a huge opportunity to service a growing industry.
  • This article will provide you with every single detail you need to know about the requirements for the C-55 license for Water Conditioning!

Jobs You Can Do With a C-55 License!

What is a Water Conditioning Contractor?

A large water filtration system with several pipes

A water conditioning contractor installs water conditioning equipment with the use of only such pipe and fittings as are necessary to connect the water conditioning equipment to the water supply system and to by-pass all those parts of the water supply system within the premises from which conditioned water is to be excluded” – CSLB.GOV

The C-55 license is the classification required in the state of California for all persons looking to bid on water conditioning projects where the cost of labor and materials exceeds $500.

Duties of a Water Conditioning Contractor

A water conditioning contractor fixing a pvc water filtration pipe outside

Water conditioning contractors engage in a wide variety of activities associated with the purification and treatment of water filtration systems.

While there is no solution for the total elimination of harmful mineral build-up in water, steps can be taken to reduce the levels of contaminants such as chloramine, lead, ammonia, and chlorine.

Their typical duties include:

  • Installation of in-home water treatment systems
  • Design and repair of under-the-sink systems
  • Carbon removal, rebedding, well water treatment
  • Water analysis reporting and microbiological activity
  • Disposal of wastewater and prevention of scaling or corrosion
  • Installing pipes, valves, and electrical connections
  • Start-up and calibration of filtration systems
  • Job site and system evaluation
  • Estimating, bidding, and accounting
  • To get the C-55 license, you will be tested on all aspects of the design, installation, and repair of water conditioning systems.

  • It will be essential to your success to become familiar with all the areas of expertise that fall under this highly specialized trade.


An underground water supply tank attached to white water tubes

Generally, a water conditioning contractor will work in a residential or commercial setting.

If a homeowner is looking to have a complex water treatment system installed in their home beyond a simple home water filter.

A water conditioning contractor would come in and assess the system or design and install a new system.

They may also be subcontracted by a General Contractor. Check out this article for an in-depth look at the General Contractor License!


Logo of the Contractors state license board. illustration features a paint brush, cement truck and saw with the letters CSLB above

The Contractors State License Board (CSLB) is the governing body for all contractors in the state of California.

Their responsibility is to protect the consumer public and ensure that anyone charging over $500 for water conditioning services is qualified and registered with the state of California. 

The C-55 License is issued to water conditioning contractors by the CSLB. 

EPA Certification

logo of the united states environmental protection agency. water conditioning contractors looking to get the c-55 license should know how to contain lead paint if it is present in homes

Understanding how to safely contain lead-based paint when altering structures built before 1978 is required by the Environmental Protection Agency

The most profitable water conditioning contractors are the ones that position themselves as the experts and are the most knowledgeable and helpful to their clients. 

Becoming EPA Certified can help you expand your business and can be completed in a one-day 8-hour course.

Staying EPA compliant is not only important to the survival of your business but also to the safety of your customers.  Learn how to get an EPA certification, in 8 hours!

BluePrint Reading Course

A construction blueprint with several pipes, screws and a wrench laying on top

It is critical for water conditioning contractors to be able to follow specific designs and symbols on construction blueprints when working on job sites.

If their installation duties are part of a larger project or involve some kind of alteration to a sink or wall, it will be very important for them to understand the design of the home.

Construction blueprints communicate important information about how a structure has been built as well as what materials are necessary or have been used for its construction.

Being comfortable with construction blueprints is an invaluable skill for all tradesmen but is especially important for those looking to get the C-55 license.

Learn How To Read Blueprints Here!

How to get a C55 license in California

Water conditioning contractors in California must prove a minimum of 4 years of journeyman-level experience. 

You must also pass a two-part state exam with the Contractor State License Board.

To qualify for an exam date you must meet the following requirements:

  • Be at least 18 years of age
  • Have a valid Driver's License or USA Issued Identification
  • Have a Social Security or ITIN #
  • Not Currently on probation or parole

You must also have:

  • 4 Years Journey Level Experience 
  • A Certifier to sign off on your experience
  • A way to prove your experience if the state asks for documentation

What is journey-level experience?

A water well, water conditioning contractors looking to get the C-55 license must have experience in well water treatment

Journeyman-level experience means that you have worked unsupervised full-time for a water conditioning or plumbing company, or contractor that holds the C-55 License.

  • A journeyman can perform all of the duties associated with his or her trade.

The CSLB will want to see four full-time years over the last ten years. The years do not need to be consecutive, but they do need to be four years in total. 

Signature of a Certifier

The following people may be used as a certifier to sign off on your experience when applying for the C-55 license:

  • Licensed General Contractor
  • C-55 License Holder
  • Fellow Employee (within the last 10 years)
  • Former Supervisor (within the last 10 years)
  • Business Associate
  • Fellow Journeyman
  • Union Representative

How to fill out the C55 License application

Your certifier will also need to provide a brief but detailed description of your knowledge and skill set.

The way this description is written will be critical to whether or not your application is accepted. For example: 

“Ed installed our water filter” is not descriptive enough.

The CSLB will want to see:

“Ed has safely connected treatment systems to existing water supply, conducted water analysis,  installed pipes, vales and installed water conditioning equipment”.

The description written by your qualifying individual will need to include the core skills required by a water conditioning contractor.

Work experience for the Contractors' License
A home water filtration system. Many water conditioning contractors run businesses repairing and maintaining simple home water filtration systems

You must be prepared to submit documentation supporting the experience you claim to have. The Contractors State License Board gives you a few ways that you can prove your experience.

  • Tax Returns
  • Check Stubs
  • Contracts
  • Material Order Invoices or Receipts

The CSLB  receives thousands of applications per month so there is a good chance they won’t document your experience.

However, if you are one of the applicants that get reviewed you will need to be ready to submit something. 

The CSLB does not accept pictures of projects.

Application Processing, Fees, and Criminal History

The time it takes to get your application processed and assigned a test date fluctuates throughout the year.

Typically you can expect:

  • 6-8 Week Application Processing Time
  • 3-4 Week wait for an Exam date

I have seen some situations where applicants got their test date sooner and somewhere they got their test date much later.

The most common reasons your application would get held up are:

  1. Time of year (processing time slows down during the holidays) 
  2. Criminal History 
  3. Proving Experience
  4. Mistakes on your application 

Application Costs for the C55 License

The Current CSLB fees are: 

Can you get a Contractor's License with a Felony in California?

a pair of black handcuffs laying on a white surface. when appying for the contractor license, you should be 100% honest about your criminal record

Having a criminal record in no way stops you from getting a C-55 License.

The truth is many applicants with criminal records get licensed in California each year…some end up obtaining multiple classifications.

The key is, to be honest on the application, even if the felony or misdemeanor happened years ago and even if it was expunged.

See the CSLB's verbiage below:

Just because you have been convicted of a crime does not automatically mean
your application will be denied. CSLB's Criminal Background Unit (CBU) reviews
all criminal convictions to determine if the crime is substantially related to
the duties, qualifications, and/or functions of a contractor. Since no two
conviction records are the same, they are reviewed on a case-by-case basis. The
criteria used by CSLB include whether the crime shows the present or potential
unfitness of an applicant or licensee to perform the functions authorized by
the license in a manner consistent with the public health, safety, or welfare.
In addition, CSLB reviews and considers any evidence of rehabilitation
submitted by the applicant or licensee. Please see the above link to the
California Code of Regulations sections 868 and 869 for more specific
information on the criteria for determining substantial relationship and

Learn more about the Background Check Process here:

BE 100% HONEST ON THE APPLICATION, because they will see everything anyway when you do fingerprinting. The CSLB handles criminal records on a case-by-case basis.

Remember, their responsibility is to protect the public.

In my experience, they are primarily concerned with criminal charges associated with Fraud, Embezzlement, or Forgery

The C55 License Exam

The exam will be:

  • 115 Questions on Contractor LAW
  • 115 Questions on Water Conditioning 
  • You will have 3 hours to complete each portion
  • The exam is multiple choice and is taken on a computer
  • Closed Book

The Water Conditioning (C-55 license) Examination is divided into four major sections:

1. Water Testing and Equipment Selection (22%)

  • Water analysis
  • System selection
  • Job site evaluation
  • Planning and Estimating

2.    Water Systems, Component Installation, and Start-Up (29%)

  • Piping and valves
  • Equipment installation
  • Drain connections/backflow
  • Electrical connections
  • Startup and calibration

3.    Troubleshooting, Maintenance, Repair, and Replacement of Water Systems and Components (34%)

  • Service and maintenance
  • Troubleshooting
  • Repair and replacement
  • Disinfection

4. Safety (15%)

  • Personnel safety
  • Handling hazardous materials
  • Environmental safety
  • Tool and equipment safety

Recommended Resources

CSLB Test Locations

The CSLB has exam centers all over the state of California. Once your
application is approved you will be given a list of locations you can go and
take the exam based on your zip code.

These are proctored facilities with cubicles where you take the exam on a
computer. The computer will have a calculator for your use. You will not be
able to bring in a phone, notes, or personal calculator to the exam center.

  • You get 18 months after your application is accepted to pass both examinations.

  • $100 per retake

Learn more about Contractor License LAW

C55 study guides and practice tests

Some things to remember:

  • The questions you will see on the exam may use outdated terms
  • Processes may be completely different from how things are done on the job site
  • You will see questions about things you may have never done before
  • Questions will be presented to you as if you are running a large-scale construction business with several employees and jobs happening all at once. 
  • Know all aspects of your trade

I have helped water conditioning contractors from all over the country get licensed in California. Many are startled by how strange the questions on the exam are.

Be as prepared as you possibly can.

Studying just 10 minutes a day consistently can dramatically increase your chances of passing the test on your first try.

Focus on and study ONLY the information that you need to pass the C-55 License.

a visual representation of the process of reverse osmosis

Water Treatment Apprenticeship

A handheld water filter system, commonly found in house holds all around america laying on top of a table with a pitcher of water in the background

If you don’t have the 4 years required journeyman-level plumbing experience to get a C-55 license, your journey begins here.

Generally, someone looking to get into this trade would begin by finding a union or plumbing apprenticeship program.

For a detailed explanation of this process, check out my article: Apprentice vs Journeyman!


Getting the C-55 License can be a huge step up in your career if you are looking to start your own water conditioning company or become an RMO!

The key is to take action and follow these steps from beginning to end. 

If you have found this article helpful feel free to drop a comment below and be sure to check back for updates!