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Water Damage Categories and Classes, Explained
Restoration companies describe water two ways. Category (1–3) is how contaminated it is, which decides what can be saved. Class (1–4) is how much was absorbed, which decides how hard drying will be. Both come from the IICRC S500 standard.
Categories
Categories: how clean is the water?
| Category | What it is | Home examples | What it means |
|---|---|---|---|
| 1: Clean | Water from a sanitary source | Broken supply line, overflowing sink | Carpet often saved if caught early |
| 2: Gray | Some contamination; could cause illness | Washing machine or dishwasher discharge, toilet overflow with urine only | Pad usually removed; cleaning and treatment |
| 3: Black | Grossly contaminated | Sewage, floodwater, toilet backup with waste | Porous materials usually removed; protective gear |
Sewage needs its own approach: sewage backup cleanup.
Classes
Classes: how much water was absorbed?
| Class | What it means | Example |
|---|---|---|
| 1 | Small area, little absorption | Part of a room with tile or sealed floors |
| 2 | A whole room; water wicked a short way up walls | Carpet and pad soaked, wet baseboards |
| 3 | The most water; often from above | Ceiling, insulation, walls and floors all wet |
| 4 | Specialty drying of dense materials | Hardwood, plaster, concrete, deep pockets of water |
Class 4 jobs take longest. See hardwood floor water damage and structural drying.
Why it matters
Why you should ask about both
Category and class drive the scope, equipment and price, and they appear on most itemized estimates. Ask which category and class the company assigned and why, and check that the bill matches. What will it cost? See the Richardson cost guide. Filing a claim? See the insurance claim guide.
FAQ
Categories and classes FAQs
What are the categories of water damage?
The IICRC S500 standard sorts water by contamination: Category 1 is clean water (like a broken supply line), Category 2 is gray water with some contamination (like washing machine discharge), and Category 3 is grossly contaminated water (like sewage or floodwater).
What are the classes of water damage?
Classes describe how much water was absorbed and how hard drying will be, from Class 1 (a small area with little absorption) to Class 4 (specialty drying of dense materials like hardwood, plaster and concrete).
Can clean water turn into Category 3?
Yes. Water that starts clean can degrade over time as it sits in carpet, wall cavities and warm conditions, and as it picks up contaminants. That’s one reason fast extraction matters.
Sources for this page
Last updated October 2026.
Not sure what kind of water you have?
Call and describe the source. Sewage needs different handling.