Categories determine the type of water while classes determine how wet building materials are.
Category 1: Coming from a sanitary source and does not pose a major threat from exposure. An example would be a tub or sink overflow with no contaminants
Category 2: Contains significant contamination and can cause various health issues if consumed. An example would be discharge from a dishwasher
Category 3: Heavily contaminated can have pathogenic agents. If consumed it can cause major damage to one’s health. An example would be a raw sewerage backup.
Class 1: Less than 5% of the combined space affected
Class 2: 5%~40% of the combined space affected
Class 3: More than ~40% of the combined space affected
Class 4: Deeply held in low evaporation materials such as plaster, wood or concrete