The short answer
The restoration industry's water damage standard, the IICRC S500, sorts water into three categories by contamination: Category 1 is clean, Category 2 is significantly contaminated and Category 3 is grossly contaminated. The category decides what can be saved, what has to be removed and what protection the crew needs, so it's one of the biggest drivers of a restoration job.
On this page
The three categories
Clean water
From a sanitary source, such as a broken supply line, a faucet left running or a water heater tank. Usually the most restorable. See burst pipe water damage.
Gray water
Significantly contaminated, such as washing machine or dishwasher discharge, or a toilet overflow with urine but no feces.
Black water
Grossly contaminated, such as sewage, toilet overflow with feces and rising floodwater from rivers and streams. See sewage backup cleanup.
Water can change category
Water that starts clean doesn't always stay clean. As it sits, it can pick up contaminants from carpet, building materials and whatever was on the floor, and warmth and time help microbes grow. That's one reason restorers move fast and why water that sat for days is handled more cautiously than a fresh leak.
What the category means for your home
| Category 1 | Category 2 | Category 3 | |
|---|---|---|---|
| Carpet | Often dried in place | Sometimes cleaned and dried; pad usually replaced | Usually removed with the pad |
| Drywall | Often dried in place if not swollen | Case by case | Usually cut out above the water line |
| Protection | Standard precautions | Gloves and cleaning | Protective equipment and containment |
The EPA's water damage guidance makes the same distinction: its drying-in-place strategies are for clean water, and it says that when water may be contaminated with sewage, protective equipment and containment are needed and an experienced professional should be consulted.
How a restorer decides the category
The technician looks at where the water came from, what it passed through and how long it has been sitting. A clean supply line that broke an hour ago is Category 1. The same water that ran through a dirty basement and sat for several days may be treated as Category 2 or 3. Anything that came up through a floor drain or toilet, or in from outside during a flood, is handled as Category 3. If you're unsure, describe the source and timing on the phone so the crew comes prepared.
What you can do while you wait
- Stop the source and keep people and pets out of dirty water.
- Wear gloves and boots if you must go near water from a drain, toilet or flood.
- Don't run the HVAC system if it could spread odors or contamination from a flooded area.
- Photograph the water and the source before cleanup starts.
Category is not the same as class
Category describes how dirty the water is. Class describes how much water there is to evaporate, from Class 1 for a small area to Class 4 for dense materials like hardwood and plaster. Both shape the job. See structural drying for the classes, and our main page on water damage restoration in the Westfield area for local help.
Sources
- EPA, Mold Remediation in Schools and Commercial Buildings, Chapter 4 (responding to water damage within 24–48 hours)
Frequently asked questions
Is water from a washing machine clean or gray water?
Washing machine discharge is generally treated as Category 2, gray water, because it can carry soaps, dirt and other contaminants.
Is floodwater considered black water?
Yes. Rising floodwater from rivers and streams is treated as Category 3 because it can carry sewage, chemicals and debris.
Can carpet be saved after a toilet overflow?
It depends on what was in the water and how long it sat. Overflow with feces is Category 3, and carpet and pad are usually removed.