Water damage basics:
Categories & Classes

Categories — how contaminated is the water?

Category describes the contamination range of the water: where it came from and what it picked up on site. Time, temperature and the materials it travelled through can change the preliminary category determination.

Category 1 — sanitary source

Water originating from a sanitary source that does not pose a substantial risk when it remains Category 1.

• Broken drinking-water supply lines
• Clean tub or sink overflows
• Appliance supply-line failures
• Direct falling rainwater before it contacts contaminated surfaces

Category 2 — significant contamination

Water containing significant contamination that may cause discomfort or sickness if contacted or consumed.

• Dishwasher or washing-machine discharge
• Toilet overflow with urine but no faeces
• Hydrostatic seepage, broken aquariums and punctured waterbeds

Category 2 water can also deteriorate to Category 3.

Category 3 — gross contamination

Grossly contaminated water that can contain pathogenic, toxigenic or other harmful agents.

• Sewage and waste-line backflows from beyond a trap
• Seawater and rising river or stream water
• Weather-related water where inspection supports gross contamination

Classes — how much drying work is there?

Class describes the absorption and evaporation load: how much wet porous surface is involved and whether moisture is deeply held. It helps plan equipment, monitoring and likely drying complexity.

Class 1

Lightest load. Wet porous materials represent less than about 5% of the combined floor, wall and ceiling surface area, with minimal absorption into low-evaporation materials.

Class 2

Significant load. Wet porous materials represent about 5% to 40% of combined surfaces, with minimal absorption into low-evaporation materials or assemblies.

Class 3

Greatest porous-surface load. Wet porous materials represent more than about 40% of the combined floor, wall and ceiling area.

Class 4

Deeply held or bound water in low-evaporation materials such as plaster, wood, concrete and masonry, or in complex assemblies such as multilayer wallboard, subfloors and gym floors. Special methods and longer drying times may be required.