Restoration professionals sort water damage into three categories based on how contaminated the water is. The category determines how the cleanup is done, what protective steps are needed and which materials can be saved.
- Category 1 is clean water, Category 2 is gray water and Category 3 is black water.
- Sewage and floodwater are always Category 3; porous materials they touch are removed.
- Clean water can degrade to Category 2 or 3 if it sits for a day or two.
- Categories describe contamination; classes describe how hard drying will be.
These categories come from the IICRC S500 standard for professional water damage restoration, which is widely used across the industry.
| Category | Also called | Common sources | Porous materials (carpet, pad, drywall) |
|---|---|---|---|
| Category 1 | Clean water | Burst supply lines, sink or tub overflows, appliance supply lines | Often dried in place if extraction is fast; pad usually replaced |
| Category 2 | Gray water | Washer or dishwasher discharge, urine-only toilet overflow, sump failures | Pad removed; other materials cleaned, treated or removed case by case |
| Category 3 | Black water | Sewage backups, floodwater, toilet backflow beyond the trap | Removed and discarded; remaining structure sanitized |
Category 1: Clean water
Water from a sanitary source that doesn’t pose a substantial risk if touched or ingested.
- Broken or burst supply lines
- Overflowing sinks or tubs with no contaminants
- Melting snow or ice from a clean source
- Appliance supply line failures
What it means: If extraction starts quickly, many materials, including carpet and some drywall, can often be dried in place. Carpet pad is usually replaced.
Category 2: Gray water
Water with significant contamination that could cause discomfort or illness if touched or ingested.
- Dishwasher or washing machine discharge
- Toilet overflow with urine but no feces
- Sump pump failures
- Aquarium or waterbed leaks
What it means: More materials may need to be removed, and cleaning and antimicrobial treatment are part of the process. Carpet pad is removed, and carpet may sometimes be cleaned and saved, depending on circumstances.
Category 3: Black water
Grossly contaminated water that may contain pathogens, toxins or other harmful agents.
- Sewage and toilet backflows from beyond the trap
- Floodwater from rivers, creeks or surface runoff
- Water that has picked up soil, chemicals or debris
What it means: Porous materials it touches, such as carpet, pad, drywall and insulation, are generally removed and discarded. Crews use protective equipment and containment, and everything that remains is cleaned and sanitized before drying.
Categories can change
Water doesn’t always stay in the category it started in. Clean water that sits for a couple of days, picks up contaminants from flooring and building materials, or starts growing bacteria in a warm space can degrade to Category 2 or even Category 3. That’s another reason fast extraction matters: a burst supply line handled the same day is a much simpler job than the same leak found three days later.
Categories vs. classes
You may also hear about water damage classes. Classes 1 through 4 describe how much water is involved and how hard it will be to dry, from a small area with little absorption to deeply saturated materials like hardwood, plaster and concrete. Categories describe contamination; classes describe the drying challenge.
Safety tips by category
- Category 1: generally safe to start moving belongings and blotting water, as long as electrical hazards are addressed.
- Category 2: wear gloves, avoid contact with skin and eyes, and wash your hands thoroughly.
- Category 3: avoid contact entirely, keep children and pets away, and let professionals handle the cleanup. See sewage cleanup and flood damage repair.
Related service: Water Damage Restoration in Littleton, CO.
Sources & industry standards
This guide is general information for Littleton-area homeowners, written with reference to the sources above. It isn’t professional, legal or insurance advice. See our editorial standards.
