Quick answer
The IICRC S500 standard uses three categories: Category 1 (clean water), Category 2 (gray water), and Category 3 (black water, which is grossly contaminated). Category 3 can contain harmful bacteria, viruses, and other agents (IICRC). Water can move to a worse category the longer it sits.
What is Category 1 (clean) water?
Water from a source that does not pose substantial harm to people. Examples:
- Broken supply lines
- Tub or sink overflows with no contaminants
- Appliance supply line failures
- Melting ice or snow, and falling rain
- A broken toilet tank or bowl with no contaminants
Examples from University of Colorado Anschutz guidelines adapted from the IICRC S500.
What is Category 2 (gray) water?
Water with significant contamination that can cause discomfort or sickness. Examples:
- Dishwasher or washing machine discharge
- A toilet bowl overflow with urine but no feces
- Sump pump failures
- Seepage from groundwater pressure
Same CU Anschutz guidelines.
Water still coming in or standing? A local restoration company can start water removal now.
Call (866) 217-4054What is Category 3 (black) water?
Grossly contaminated water that can contain pathogenic, toxigenic, or other harmful agents. Examples include sewage, waste line backflows from beyond a trap regardless of how the water looks, seawater flooding, and rising water from rivers or streams (IICRC 2026 position statement).
For Category 2 or 3 water, cleanup and removal should happen before drying, and the crew should use contamination controls and protective gear (same source).
How does clean water become contaminated over time?
Time and temperature can change the category (IICRC). Clean water picks up contaminants from carpet, soil, and building materials. Under guidelines adapted from the standard, materials hit by gray water and not dried within 48 hours are treated as Category 3 (CU Anschutz). That is one more reason to start fast.
What does the water category mean for your belongings?
- Category 1: most materials can be extracted, cleaned, and dried.
- Category 2: wet carpet pad is typically removed and discarded, and carpet is cleaned, sanitized, and dried on both sides.
- Category 3: carpet and pad are removed, wet drywall and insulation are cut out, and remaining framing is cleaned and sanitized before rebuilding.
Outcomes from the SCRT summary of the S500.
How is water damage category different from class?
Category describes how dirty the water is. Class describes how much water there is and how much got absorbed, which sets how much drying equipment the job needs (SCRT). A small sewage spill is Class 1, Category 3. A burst pipe that soaks three rooms might be Class 2 or 3, Category 1.
Common questions
Who decides the category?
The restorer makes a preliminary call at the start of the job, and the IICRC says that call should be based on actual conditions observed at the site. If there is a real question, testing can settle it.
Is storm rainwater automatically Category 3?
No. In 2026 the IICRC S500 consensus body said water from weather-related events is not automatically Category 3. It depends on whether contaminated water actually entered the home (IICRC announcement).
Is standing black water in the basement dangerous?
It can be. Keep kids and pets out, avoid skin contact, do not run fans that spread it around, and leave cleanup to a crew with protective gear.
Related guides
Sources:
- IICRC: Category of water damage and weather-related events (2026 position statement)
- IICRC: S500 consensus body position statement announcement (March 2026)
- University of Colorado Anschutz: Water damage remediation guidelines (adapted from IICRC S500)
- SCRT: Consumer, restorer and adjuster right-to-know report on the S500