The three categories come from the cleaning and restoration industry, where the IICRC S500 standard for water damage restoration is widely used. The names below are the industry’s terms. If a provider uses them, this is what they mean.
The three categories
| Category | Common name | Typical sources | What it means |
|---|---|---|---|
| 1 | Clean water | Broken supply line, faucet or tub overflow with clean water, rainwater from the sky | Starts from a sanitary source with no substantial contamination |
| 2 | Gray water | Washing machine or dishwasher discharge, toilet overflow with urine but no feces, sump pump failure | Significant contamination; can cause illness if swallowed or touched |
| 3 | Black water | Sewage, floodwater from outside, water from a rising river or storm surge | Grossly contaminated; may contain harmful organisms |
What changes by category
- Category 1: Many materials can be dried in place if the response is fast.
- Category 2: More materials, especially porous ones, may need cleaning or removal.
- Category 3: Porous materials are usually removed and discarded, and surfaces are cleaned and disinfected by trained crews. See sewage backup and flood cleanup.
Water can get worse
Clean water that sits for a long time, or flows through dirty materials, can move to a more contaminated category. This is one reason the first 24 to 48 hours matter. The U.S. EPA advises drying water-damaged areas and items in that time to help prevent mold.
Why you should not decide alone
You cannot always tell the category by looking. Clear water from a flood can be Category 3. Ask a provider to explain how they classed the water and why. If you are unsure, treat the water as contaminated: keep people and pets out and wear protection.
Note on sources
We could not verify the exact category definitions from the standard itself, since the full standard is sold by IICRC. The table above summarizes how the categories are commonly described. Ask your provider which definitions they use.