C-55 Water Conditioning Contractor license in California

Updated November 1, 2026 · Official name from CSLB's classification list

• 312licenses hold C-55
• 96.6%Clear (CA addresses)
• 40.4%workers' comp exempt (all: 49.6%)
• 100%contractor's bond on file
• 18 yrsmedian time licensed
• 67%businesses, not sole owners

A C-55 contractor installs water conditioning equipment such as softeners and filtration units. The license allows only the pipe and fittings needed to connect the equipment to the water supply and to bypass parts of the system that shouldn't get treated water.

That narrow piping limit is the main thing to understand. A C-55 can hook a softener into your main line, but a larger repipe to reach the equipment is plumbing work.

Typical work under C-55

• Whole-house water softeners
• Whole-house filtration systems
• Reverse-osmosis units
• Bypass loops for hose bibs and irrigation
• Replacing existing conditioning equipment

Work that needs a different license

• Repiping the house: C-36 Plumbing
• Well pump and pressure tank work: C-57 Well Drilling
• A new electrical outlet for the unit: C-10 Electrical

Tips before hiring

• Ask for a water test before buying equipment, and ask who runs it.
• Ask about ongoing costs: salt, filters and service visits.
• If a seller pushes a contract at your kitchen table, you generally have three business days to cancel, or five if you are 65 or older.
• Ask whether the drain line for a softener or RO unit can reach a proper drain where it will sit.

Where C-55 contractors are

The cities with the most C-55 license holders in CSLB's current file:

1. Fresno: 10
2. Bakersfield: 9
3. San Diego: 9
4. Santa Rosa: 9
5. Salinas: 6
6. San Jose: 5
7. Costa Mesa: 4
8. Livermore: 4
9. Los Banos: 4
10. Oxnard: 4

How to verify a C-55 license

1. Search the business or license number here and confirm C-55 is listed on the profile.
2. Check the same number on CSLB's Instant License Check.
3. Read our full guide to checking a contractor license.

Related license types

• C-36 Plumbing Contractor
• C-57 Well Drilling Contractor

Source: CSLB public data · Updated November 1, 2026 Status can change at any time. Verify on CSLB's Instant License Check.

More license types: ← C-54 Ceramic and Mosaic Tile Contractor · C-57 Well Drilling Contractor →