C-55 Water Conditioning Contractor License in California
The C-55 Water Conditioning license covers installing water softeners, filtration and other water conditioning equipment.
Quick answer
The C-55 Water Conditioning Contractor license lets you contract for water conditioning work in California on jobs that require a building permit, use employees, or total $1,000 or more in labor and materials. To qualify you need four years of journey-level experience in the last ten years, an approved CSLB application, and a passing score on the Law & Business exam and the C-55 trade exam.
- Classification
- C-55 Water Conditioning Contractor
- License type
- Specialty (C)
- Exams
- Law & Business + C-55 trade exam
- Experience
- 4 years at journey level or higher, within the last 10 years
- Application fee
- $450 (original application)
- Initial license fee
- $200 sole owner · $350 other entities
- Contractor bond
- $25,000
- Workers’ compensation
- Workers’ comp certificate, or exemption if no employees
What a C-55 Contractor Can Do
CSLB definition: 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. (California Code of Regulations, Title 16, Division 8, Article 3; condensed. See the full text on CSLB.ca.gov.)
Typical C-55 work
- Water softener installation
- Whole-house filtration
- Reverse osmosis systems
- By-pass piping for conditioned water
Needs a different license
- General plumbing beyond connecting the equipment (C-36)
The C-55 only allows the pipe and fittings necessary to connect the equipment. Plumbing contractors (C-36) can also install water conditioning equipment.
C-55 License Requirements
CSLB uses the same core requirements for every classification. For the C-55, the qualifying individual (you, or the RMO/RME for a company) must:
- Be at least 18 years old.
- Have at least four full years of experience in water conditioning work within the last ten years, as a journeyman, foreman, supervising employee, contractor or owner-builder.
- Have that experience certified by someone with firsthand knowledge of your work, such as an employer, foreman, fellow journeyman, building inspector or homeowner.
- Pass the Law & Business exam and the C-55 trade exam, and complete CSLB’s asbestos open-book exam.
- Complete Live Scan fingerprinting and CSLB’s background review.
You may receive up to three years of credit toward the four-year requirement for technical training, apprenticeship or related education, but at least one year must be practical experience. There is no education requirement to get a California contractor license.
How to Get a C-55 License: Step by Step
- Confirm your classification. Compare your work with the C-55 scope above and the related classifications below.
- Document your experience. Gather proof of four years of water conditioning experience and line up a qualified person to certify it.
- Apply to CSLB. Submit the original application with the $450 fee. CSLP can help prepare your application so it is not returned for corrections.
- Get fingerprinted. Complete Live Scan once CSLB accepts your application.
- Study and pass your exams. Pass the Law & Business exam and the C-55 trade exam. Both are multiple choice.
- Meet issuance requirements. File your $25,000 contractor bond, workers’ compensation information, asbestos open-book exam and the initial license fee.
How Much Does a C-55 License Cost?
These are CSLB’s published fees. Bond premiums, insurance and exam preparation are separate costs that depend on your situation.
| Item | Cost |
|---|---|
| Original application (one classification) | $450 |
| Initial license fee | $200 sole owner · $350 non-sole owner |
| Live Scan fingerprinting | $32 DOJ + $17 FBI + site rolling fee |
| Contractor bond | $25,000 bond (you pay an annual premium) |
| Active renewal (every two years) | $450 sole owner · $700 non-sole owner |
| CSLP online exam prep | From $595 (Fast Track) |
Fees verified on CSLB’s fee schedule in November 2026. CSLB can change fees, so confirm before you apply.
How to Prepare for the C-55 Exams
CSLP has prepared California contractors for their CSLB exams since 2013. Our C-55 preparation covers both the Law & Business exam and the C-55 trade exam with:
- Updated 2026 online classes in English and Spanish
- Weekly live online classes with Q&A
- Online law and trade books with practice questions
- Per-chapter practice quizzes (Plus and Premium)
- Application processing help
- Optional 2-day in-person bootcamp
Study 100% online at your own pace with online courses, or finish with an intensive in-person CSLB exam bootcamp at a CSLP location.
Content reviewed against CSLB sources: November 2026
- CSLB: C-55 Water Conditioning Contractor classification
- CSLB: Qualifying experience for the examination
- CSLB: Issuing my license (bond, workers’ comp, fees)
- CSLB: List of all fees
Online California Contractor License Courses
Prepare for your California CSLB Law & Business and Trade exams with flexible online contractor license courses designed for real working contractors. Choose from three study plans with 24/7 online access, bilingual support, weekly live classes, and expert guidance throughout the licensing process.
Fast Track
$595
- 2026 Updated Classes
- Online Law Book
- Online Trade Book
- Weekly Live Online Classes
- Application processing
- 24/7 Online Access
Plus
$1,395
- Everything in “Fast Track”
- Plus:
- Law & Business Flash Cards
- Per Chapter Practice Exams
- Extended Study Time
- Physical Law & Trade Books
Premium
$1,595
- Everything in “Plus”
- Plus:
- Business Launch Checklist
- Digital Business Card ($200 value)
- Double Study Time vs. “Plus”
All Online Course Packages Include:
Bilingual Lessons
English & Español
Weekly Live Classes
Online Only
Law & Trade Books
English & Español
Proven Results
20,000+ Graduates
C-55 License FAQs
What can I do with a C-55 license?
The C-55 Water Conditioning license covers installing water softeners, filtration and other water conditioning equipment. See the official CSLB definition above for the full legal scope.
How much experience do I need for a C-55 license?
You need at least four full years of journey-level experience (or as a foreman, supervisor, contractor or owner-builder) in water conditioning work within the last ten years. Up to three years can be credited for qualifying education, apprenticeship or technical training.
What exams do I take for the C-55 license?
You take two CSLB exams: the Law & Business exam and the C-55 trade exam. Both are multiple choice. New applicants also complete CSLB’s asbestos open-book exam.
How much does it cost to get a C-55 license?
CSLB charges a $450 application fee and an initial license fee of $200 for a sole owner or $350 for other business types. You also need a $25,000 contractor bond, fingerprinting fees and, if required, workers’ compensation insurance. CSLP online exam prep starts at $595.
Can a C-55 contractor do plumbing repairs?
No. The C-55 is limited to the pipe and fittings needed to connect and by-pass water conditioning equipment. Other plumbing requires the C-36.
Can I study for the C-55 exam online or in Spanish?
Yes. CSLP’s online courses include bilingual lessons in English and Spanish, weekly live online classes and law and trade books. You can also join an in-person bootcamp at select CSLP locations. Compare course options.