Category 3 water

What it means

Category 3 is the most contaminated of the three water categories in the ANSI/IICRC S500 standard. The 2021 edition defines it as water that is “grossly contaminated” and can contain pathogenic, toxigenic or other harmful agents. Its examples include sewage, wasteline backflows from beyond a trap, all seawater flooding, and rising water from rivers or streams.

In a February 2026 position statement, the S500 consensus body said wind-driven rain and other weather-related water are not automatically Category 3. The restorer has to inspect and decide whether the water is actually grossly contaminated.

Why it matters to your health and your bill

Category 3 changes both safety and cost. EPA advises calling a professional when water damage involves sewage or other contaminated water. Expect more protective gear and more removal of soaked porous materials, which makes Category 3 jobs larger and pricier than clean-water jobs. It also means you should stay out of the area if you can. If an estimate labels storm water as Category 3, ask what evidence of contamination the restorer found. If sewage came up through a drain, start with our steps for a sewage backup.