Licensed water conditioning contractor installing a whole-house softener

Become a Licensed C-55 Water Conditioning Contractor

The C-55 Water Conditioning classification is a focused specialty, installing water softeners, filtration, and treatment equipment and connecting it to a building's water supply.

View Exam Prep Programs

Requirements

Minimum age: 18+ is CSLB's normal applicant path. A minor may qualify only after a court appoints a guardian (BPC §7065.5)
Experience required: 4 full-time-equivalent years of journey-level experience within the past 10 years; CSLB prorates part-time work
Contractor bond: $25,000

About the Exam

Exam format: 2 parts (Law & Business + Trade)
Law & Business exam: 115 questions
School-observed scores: 65% Law / 63% Trade; not published as fixed by CSLB
Application fee: $450

License renews every 2 years. Governing code: CCR §832.55

About this classification

What does a C-55 Water Conditioning contractor do?

A C-55 Water Conditioning Contractor installs water-conditioning equipment using only the pipe and fittings necessary to connect that equipment to the water supply system and to bypass the excluded parts of the system. (Per California Code of Regulations, Title 16, §832.55.)

The C-55 is a narrow, focused license. California authorizes a C-55 contractor to install softeners, filtration, and treatment equipment and tie it into existing plumbing with a connection and bypass, but not to perform general plumbing. The boundary to remember: the C-55 hooks up conditioning equipment; full water-supply and drainage systems require a C-36 (Plumbing) license.

Official source: CSLB C-55 classification · CSLB fee schedule Last reviewed: March 2026

Scope of work

Whole-house water softener installation
Point-of-entry reverse-osmosis (RO) systems
Scale-reduction and pH-adjustment systems
Filtration and treatment equipment
Conditioner hookup with bypass valve
Connection of equipment to the existing water supply
Equipment upgrades and replacements

High-demand specialties

Whole-House Softeners, Hard-water areas across California drive steady demand
Reverse Osmosis, Point-of-entry and point-of-use RO for water quality
Scale & pH Treatment, Protecting plumbing and appliances from hard-water damage
Equipment Upgrades, Replacing aging conditioning systems is a recurring service line

Important notes

The C-55 is limited to connecting conditioning equipment to the water supply with a bypass, it does not authorize general plumbing. Full supply, drainage, and gas work requires a C-36 (Plumbing) license.
A C-55 contractor treats and conditions water; drilling wells and supplying water from the ground is C-57 (Water Well Drilling) scope.
Because the scope is narrow, many water-treatment businesses pair the C-55 with a C-36 to handle broader plumbing work.
Any water-conditioning project over $1,000 requires a licensed contractor. California also requires workers' compensation coverage for licensees.

The CSLB exam

What's on the C-55 Water Conditioning exam?

California requires you to pass a two-part CSLB exam: the Law & Business exam (the same for every classification) and the C-55 Water Conditioning trade exam. CSLS has observed scores of 65% for Law & Business and 63% for the C-55 trade exam. CSLB does not publish fixed passing scores and may vary them by exam version.

Law & Business

Same for all classifications

115 questions, multiple choice, computer-based
3.5 hours allotted
Topics: California contractor law, business management, safety, estimating, project management

C-55 Trade Exam

Water Conditioning-specific

about 100 questions, multiple choice, computer-based
3.5 hours allotted
Topics: water chemistry and hardness, softeners and filtration, reverse osmosis, equipment connection and bypass, treatment system sizing, backflow protection, plumbing code basics

How to Get Your C-55 Water Conditioning License

Step 1

Qualify

18+ is CSLB's normal applicant path. A minor may qualify only after a court appoints a guardian (BPC §7065.5). You also need a valid SSN/ITIN and 4 full-time-equivalent years of journey-level water conditioning experience within the past 10 years; CSLB prorates part-time work. Up to 3 years may be substituted with approved education or apprenticeship.

Step 2

Apply to CSLB

Submit your application, get fingerprinted, and pay the $450 application fee. Processing times vary; check the CSLB's current processing times.

Step 3

Study & Prepare

Prepare for both exam parts, on your own or with a CSLS exam prep program. 99% of CSLS students pass on their first try, backed by our 100% Money-Back Guarantee.

Compare programs

Step 4

Pass the Exam

Two parts: Law & Business (115q, 3.5 hrs) + C-55 Trade. Multiple choice, computer-based. CSLS has observed scores of 65% Law & Business / 63% C-55 Trade; CSLB does not publish fixed passing scores and may vary them by exam version.

Step 5

Get Licensed

Post your $25,000 contractor bond, pay the $200 license fee, and receive your C-55 license. You're officially in business.

Step 1

Qualify

Step 2

Apply to CSLB

Submit your application, get fingerprinted, and pay the $450 application fee. Processing times vary; check the CSLB's current processing times.

Step 3

Study & Prepare

Prepare for both exam parts, on your own or with a CSLS exam prep program. 99% of CSLS students pass on their first try, backed by our 100% Money-Back Guarantee.

Compare programs

Step 4

Pass the Exam

Step 5

Get Licensed

Post your $25,000 contractor bond, pay the $200 license fee, and receive your C-55 license. You're officially in business.

Exam Prep Programs

Compare C-55 Water Conditioning Exam Prep Programs

Every program prepares you for the required CSLB exam for C-55 Water Conditioning. Our 99% first-time pass rate is backed by the 100% Money-Back Guarantee on eligible programs.

Feature-by-feature comparison of all four CSLS exam prep programs
Features	Most Popular All-Inclusive C-55 Water Conditioning $1,195.00 Value: $2,500	Live Online C-55 Water Conditioning $695.00 Value: $995	Crash Course C-55 Water Conditioning $495.00 Value: $695	Home Study C-55 Water Conditioning $295.00 Value: $395
Best For	Comprehensive prep with maximum support	Remote learners wanting live instruction	Experienced pros with an exam date soon	Self-directed independent learners
Law & Business Classes	4 Classes + Full-Day Review	4 Live Online + Review	Full-Day Review Only	Not included
Trade Math Training	30-Day Interactive + Review	Online Video Review	14-Day Crash Course	Not included
Test-Taking Skills Seminar	1-Day In-Person	1-Day Online	Not included	Not included
Law & Business Materials	Online; binder add-on available	Online; binder add-on available	Online; binder add-on available	Online; binder add-on available
Trade-Specific Materials	Online; binder add-on available	Online; binder add-on available	Online; binder add-on available	Online; binder add-on available
Study Materials	Full Online Suite	Online Materials + Audio/Video	Online + Audio/Video	Online + Audio
Online Videos	Full Suite: L&B, Trade, H&S, Math	Audio + H&S + Math Videos	Audio + H&S + Math Videos	L&B Audio + H&S Video
Law & Business Practice Exams	6 Months	2 Months	30 Days	30 Days
Trade Practice Exams	6 Months	2 Months	30 Days	30 Days
School Location Access	25+ Locations	25+ Locations	25+ Locations	Self-Study Only
Application Assistance	Preparation & Review	Review Only	Review Only	Not included
Money-Back Guarantee	Included	Included	Included	Not included
Bond Fee Discount	50% off first-year bond, up to $120	Not included	Not included	Not included
Retail Value	$2,500	$995	$695	$395
Choose a program	Get All-Inclusive	Get Live Online	Get Crash Course	Get Home Study

Not sure which fits? Call 800-809-6463. Prices and inclusions are subject to change.

Labor Day

Labor Day Promo 2026

$1,449.00 $795.00

Offer ends in

Days

Hours

Min

Sec

This offer has ended.

Valid through 12:00 am PDT, October 1, 2026.

Get this bundle View offer details

What our Water Conditioning students say

Free Resources

Try a free C-55 Water Conditioning practice exam

Test your knowledge with a free 40-question practice exam and get 14 days of online access.
No credit card required.

Common Questions

C-55 Water Conditioning license FAQ

Plan on 2–4 months from application to license-in-hand. That covers CSLB processing (typically 2–4 weeks), scheduling and passing both exams, and posting your $25,000 bond. With CSLS exam prep, most students are exam-ready in 4–6 weeks.

4 full-time-equivalent years of journey-level water conditioning experience within the past 10 years; CSLB prorates part-time work. Qualifying work may be as a journeyperson, foreperson, supervising employee, contractor, or owner-builder. Up to 3 years can be satisfied with approved technical training or education. CSLB verifies the experience you claim, so keep records of the systems you've installed.

A C-55 (Water Conditioning) contractor installs treatment equipment, softeners, filtration, RO, and connects it to the existing water supply with a bypass. That's the limit of the scope. A C-36 (Plumbing) contractor handles full plumbing: supply, drainage, venting, gas, and water heating. If you only install and hook up conditioning equipment, the C-55 is enough; if you do general plumbing, you need the C-36.

If installing and connecting water-conditioning equipment is your business, the C-55 is the license built for it. A C-36 (Plumbing) contractor can also install softeners as part of general plumbing work. The C-55 is the focused, lower-barrier path for a water-treatment specialist.

Budget about $885 minimum before exam prep: $450 for the application (both exams), $200 for initial license issuance, roughly $150 for your first year of $25,000 bond premium, and about $85 for fingerprinting. The bond is a premium, not cash you tie up.

The C-55 trade exam is computer-based and covers water chemistry and hardness, softeners and filtration, reverse osmosis, equipment connection and bypass, and treatment-system sizing. You need the current version-specific CSLB passing score to pass. With CSLS exam prep, 99% of students pass on their first attempt, backed by our 100% Money-Back Guarantee.

It depends on the work you do. If you specialize in installing and servicing water-treatment equipment, the C-55 covers your scope with a narrower exam. If you also want to perform general plumbing, repiping, drains, gas, water heaters, the C-36 (Plumbing) is the broader license. Many water-treatment businesses eventually add a C-36 to widen what they can bid.

CSLB evaluates reciprocity case-by-case (BPC §7065.4) and may waive the trade exam if your out-of-state license has been in good standing for the past five years; CSLB names no fixed list of reciprocal states. If you hold an equivalent active license in one of those states, your C-55 trade exam may be waived, but you still must pass the California Law and Business exam and meet all other licensing requirements.

Since 1985

40+ Years

200,000+

Students Licensed

99% Pass Rate

First-Time

100% Money-Back Guarantee

Tuition Refund

Become a Licensed C-55 Water Conditioning Contractor

What does a C-55 Water Conditioning contractor do?

Scope of work

High-demand specialties

Important notes

What's on the C-55 Water Conditioning exam?

Law & Business

C-55 Trade Exam

How to Get Your C-55 Water Conditioning License

Qualify

Apply to CSLB

Study & Prepare

Pass the Exam

Get Licensed

Qualify

Apply to CSLB

Study & Prepare

Pass the Exam

Get Licensed

Compare C-55 Water Conditioning Exam Prep Programs

Labor Day Promo 2026

What our Water Conditioning students say

Try a free C-55 Water Conditioning practice exam

C-55 Water Conditioning license FAQ

Ready to get your C-55 Water Conditioning license?

Select Your Trade Classification

Exam Prep Programs, Side by Side