Water Damage Categories and Classes Explained
Restoration contractors use two scales from the IICRC S500 standard: the category describes how contaminated the water is, and the class describes how much water there is and how hard it will be to dry.
Updated November 12, 2026 · By the Water Restoration Raleigh team
Water damage category describes contamination: Category 1 is clean water, Category 2 is gray water with some contamination, and Category 3 is black water such as sewage or outside flood water. Water damage class describes how much water and how hard drying will be, from Class 1 (small area, little absorption) to Class 4 (specialty drying for materials like hardwood, plaster or concrete).
Water categories: how contaminated is it?
Clean water
From a sanitary source, such as a broken supply line, a leaking water heater or an overflowing sink.
Gray water
Some contamination, 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, or rising flood water from outside.
Category can change. Clean water that sits for a few days, or picks up contaminants from the materials it touches, can become Category 2 or 3.
Water classes: how much water, and how hard to dry?
| Class | What it means |
|---|---|
| Class 1 | Small amount of water, mostly on low-porosity materials. Least drying needed. |
| Class 2 | A whole room or more, carpet and pad wet, water wicking up walls. |
| Class 3 | The most water, often from overhead, with ceilings, walls, insulation and floors saturated. |
| Class 4 | Specialty drying for materials that hold water tightly, such as hardwood, plaster, brick or concrete. |
Why this matters to you
- Category decides what can be saved. Porous materials wet with Category 3 water are usually removed.
- Class decides how much equipment and time the drying takes.
- Both show up on the estimate and in insurance documentation.
Frequently asked questions
What category is water from a toilet?
An overflow with only clean water from the tank or bowl is usually Category 1 or 2. An overflow with feces is Category 3.
What is the IICRC S500?
It is the industry standard for professional water damage restoration published by the Institute of Inspection, Cleaning and Restoration Certification (IICRC).
Can Category 1 water become Category 3?
Yes. Water that sits, or that picks up contaminants as it travels, can get worse over time.
Related help
Water in your home right now?
Stop the water, stay away from wet electrical areas, and take photos. Our first-steps checklist walks you through the next hour.