Category 1, 2 and 3 water: what changes in the restoration scope

Last updated November 5, 2026 · Written by the First Response Restoration team

Not all water damage is the same. The industry standard for water damage restoration, IICRC S500, sorts water into three categories based on how contaminated the source is. The category changes what is safe to dry in place, what must be removed and what protection the crew needs.

The three categories

Category 1: clean water

Water from a sanitary source, such as a broken supply line, a leaking faucet or an overflowing sink with clean water. Most materials can usually be dried in place when the work starts quickly.

Category 2: significantly contaminated water

Water that can cause illness if exposed or consumed, such as discharge from a washing machine or dishwasher, or overflow from a toilet that contains urine but not feces. Porous materials such as carpet cushion are commonly removed, and surfaces are cleaned and treated.

Category 3: grossly contaminated water

Water that is highly contaminated, such as sewage, rising flood water from outside, or standing water that has supported microbial growth. Affected porous materials such as carpet, cushion and drywall are generally removed and disposed of, and the crew uses full protective equipment and containment.

Water can move up a category

Category is not fixed. Time and temperature can allow Category 1 water to degrade into Category 2 or 3 if it sits. In Houston’s heat, this can happen faster than many people expect. This is one more reason to start extraction as soon as possible.

The four classes: how much water is in the structure

Category describes contamination. The class describes how quickly water is expected to evaporate, which depends on how many materials are wet and how porous they are.

• Class 1: little water absorbed, low-porosity materials, a small area.
• Class 2: a whole room affected, with carpet and cushion wet and moisture wicked up the walls.
• Class 3: water coming from above, saturating ceilings, walls, insulation and floors.
• Class 4: specialty drying, where water is held deep in low-permeance materials such as hardwood, plaster or concrete.

How category and class change the scope

Factor	What it changes
Category	What is removed versus dried, cleaning and treatment steps, protective equipment and containment, how materials are disposed of.
Class	The amount and type of drying equipment, the likely drying time and the monitoring plan.
Time since the loss	Whether materials can still be saved, and whether the category has worsened.

What this means for your estimate

Two losses with the same square footage can have very different scopes. A Category 1 supply-line leak that is caught early might need extraction and drying only. A Category 3 sewage backup can require removing flooring and drywall, cleaning, and a longer containment and verification process. Your restoration team should explain the category and class they identified and how they measured it, and document the moisture readings that support it.

Read more about how we handle these jobs on our water damage restoration service page, and see our Houston service area page to reach the local team.