Category describes how contaminated the water is (the health hazard). Class describes how much water there is and how hard it will be to dry (the evaporation load). Every water loss has one of each.
- Category 1 — clean water
- From a sanitary source: a supply line, a tub overflow, rainwater. Safe to handle, but it degrades to Category 2 within roughly 48–72 hours, or sooner in warm conditions or if it contacts contaminated materials.
- Category 2 — gray water
- Significantly contaminated — dishwasher or washing-machine discharge, toilet overflow with urine (no feces), a broken aquarium. Can cause illness if ingested. Degrades to Category 3 over time.
- Category 3 — black water
- Grossly contaminated — sewage, rising flood or ground surface water, seawater, or any Category 2 water left long enough. Contains pathogens and toxins; porous affected materials are typically removed, not dried.
- Class 1 — least water
- A small area, minimal moisture absorbed by low-porosity materials. The fastest drying scenario.
- Class 2 — significant
- A whole room where water has wicked up walls less than 24 inches and saturated carpet and cushion.
- Class 3 — greatest
- Water came from overhead: saturated ceilings, walls, insulation, and subfloor. The largest evaporation load.
- Class 4 — specialty / bound water
- Deeply held water in low-permeance materials — hardwood, plaster, concrete, crawlspaces. Needs specialty methods (heat, low-GPP) and longer drying.
Per IICRC S500. Category can change as time passes and as water contacts materials — always classify at inspection and re-assess.
Category vs. Class — don’t confuse them
Category is about health: how contaminated the water is, which drives whether materials are cleaned, dried, or removed. Class is about drying difficulty: how much water and how deeply it is held, which drives how much equipment and time the job needs. A loss can be Category 1, Class 3 — clean water, but a lot of it, overhead.
Why it drives the whole job
The category sets the health and demolition plan; the class sets the equipment and schedule. Both belong in the documentation from day one, because insurers reconcile the drying plan and the invoice against them — and category can escalate with time, which changes everything.
Frequently asked
What is the difference between water damage category and class?
Category describes how contaminated the water is (1 clean, 2 gray, 3 black) and drives the health and demolition plan. Class describes how much water is present and how hard it is to dry (1 least to 4 specialty) and drives the equipment and schedule.
What is Category 3 water?
Category 3 (“black water”) is grossly contaminated water containing pathogens — sewage, rising flood or ground surface water, seawater, or any lower-category water left long enough to degrade. Porous affected materials are usually removed rather than dried.
What is Class 4 water damage?
Class 4 is deeply held “bound” water in low-permeance materials such as hardwood, plaster, concrete, and crawlspaces. It requires specialty drying methods — heat and low-GPP air — and takes longer than Classes 1–3.
More free tools
This knowledge, built into the software
RestoredOS runs the whole job on the same field knowledge behind these tools — drying logs, moisture mapping, scope, and billing.