Water damage categories: clean, grey and black water
Restoration companies classify water by how contaminated it is, following the IICRC S500 standard. The category decides what can be saved, how it's cleaned and what the job costs.
Updated October 2026 · Sources are linked in the text.
The three categories
The IICRC's S500 standard sets out procedures and precautions for professional water damage restoration (IICRC S500 Standard for Professional Water Damage Restoration). In everyday terms:
| Category | Also called | Typical sources |
|---|---|---|
| Category 1 | Clean water | Broken supply line, faucet, water heater |
| Category 2 | Grey water | Washing machine or dishwasher discharge, toilet overflow with urine only |
| Category 3 | Black water | Sewage, rising flood water, toilet backflow with waste |
Water can get worse over time
Clean water doesn't stay clean. As it sits and picks up dirt and materials, and as bacteria grow, a clean-water leak can become grey or even black water. That's another reason to act within the 24–48-hour window the EPA recommends for drying (EPA: A Brief Guide to Mold, Moisture and Your Home).
What changes with contamination
- Category 1: many materials can be dried and kept.
- Category 2: more cleaning and disinfection; some porous items may need to go.
- Category 3: porous materials like carpet, pad, drywall and insulation that were soaked are usually removed; crews use protective equipment and disinfect.
Safety with dirty water
Keep children, pets and anyone with health problems away from grey or black water, wear boots and gloves, and wash hands thoroughly. Sewage cleanup is a job for professionals.
Quick answers
Is a toilet overflow category 2 or 3?
Overflow with only urine is generally treated as grey water; anything with feces or from a sewer backup is black water.
Can carpet be saved after water damage?
Often after clean water if dried quickly. After sewage or flood water, carpet and pad are normally removed.