Water Damage Categories 1, 2 and 3 and Classes 1 to 4, Explained

Category 1

Clean water

From a sanitary source: a broken supply line, an overflowing sink with no contaminants, a water heater, melting ice or snow.

Category 2

Gray water

Significant contamination that could cause illness: washing machine or dishwasher discharge, a toilet overflow with urine but no feces, an aquarium, a failed sump.

Category 3

Black water

Grossly contaminated: sewage, toilet overflow with feces, rising floodwater from rivers or streams, and water that has sat long enough to grow microbes.

Why the category matters

Category 1 jobs are mostly about drying. Carpet, padding and drywall can often be saved if extraction and drying start quickly.

Category 2 adds cleaning and antimicrobial treatment. Carpet padding is usually replaced, and porous materials that soaked it up may need to come out.

Category 3 is a contamination job. Technicians wear protective equipment, porous materials that the water touched (carpet, pad, drywall, insulation, upholstered furniture) are generally removed and discarded, and everything left is cleaned and sanitized. Children, older adults, pregnant people and anyone with a weakened immune system should stay out until it's done.

Water gets dirtier as it sits

Category is not fixed. Clean water picks up contaminants from flooring, wall cavities and dust, and microbes multiply in warm, still water. A clean supply-line leak left for a few days can become Category 2 or 3 water. That's the practical reason to start extraction the same day.

Classes: how much is wet

The S500 standard also sorts jobs into classes based on how much material got wet and how hard it will be to dry. The class drives how much drying equipment goes in and how long it runs.

Class	What's wet	Typical example
Class 1	A small area; little water absorbed into porous materials	A dishwasher leak caught quickly on a tile floor
Class 2	A significant share of the room, such as carpet and the lower part of walls	A washing machine hose that ran for an hour
Class 3	Most of the room's surfaces, often because water came from above	A burst pipe in an upstairs bathroom soaking the ceiling below
Class 4	Water held deep in dense materials such as hardwood, plaster, brick or concrete	A flooded basement with a finished hardwood floor

Questions to ask the restoration company

What category and class did you assign, and why?
Which materials can be dried in place, and which need to be removed?
Will you take and record moisture readings every day until the job is dry?
Are your technicians IICRC certified in water damage restoration?

Frequently asked questions

Is water from a toilet Category 2 or Category 3?

A toilet overflow with urine but no feces is generally treated as Category 2. An overflow containing feces, or any sewage backing up from a drain, is Category 3.

Is rainwater coming through the roof clean water?

Rain is usually Category 1 when it first comes in, but it picks up dirt from roofing, insulation and attic dust on the way. Wet insulation and ceiling drywall from a roof leak often have to come out regardless of category.

Can I clean up Category 3 water myself?

It isn't recommended. Sewage and floodwater can carry bacteria, viruses and parasites. Porous materials it touched generally have to be removed and discarded, and the space sanitized, by people wearing protective equipment. Children, older adults, pregnant people and anyone with a weakened immune system should stay out until it's done.

What is the difference between a water damage category and class?

Category describes contamination: how dirty the water is. Class describes the extent: how much of the room is wet and how much water the materials absorbed. A small, clean leak is Category 1, Class 1. A sewage backup across a finished basement could be Category 3, Class 2 or 3.

Clean, gray or black water: the three categories of water damage