Water Damage Categories.
Cat 1, Cat 2, Cat 3 — Explained.

Category 1 is water from a sanitary source — supply lines, broken toilet tank (no waste), broken faucet, sprinkler discharge. It poses no substantial risk to humans IF addressed promptly. Category 1 begins degrading to Category 2 the moment it contacts contaminated materials (carpet pad, drywall paper, baseboards) and within 24-48 hours becomes Cat 2 by default.

Category 2 — gray water — contains significant chemical, biological, or physical contamination and can cause illness on contact or ingestion. Sources include washing machine overflow, dishwasher discharge, broken aquariums, hydrostatic seepage from outside, and any Cat 1 water that has sat 24-48 hours. Cat 2 requires PPE, antimicrobial treatment, and removal of porous materials that absorbed the water.

Category 3 — black water — is grossly contaminated and can cause serious illness or death. Sources include sewage backflow, ground-source flooding (river / storm runoff carrying soil and chemicals), toilet overflow with feces, and any Cat 2 water that has sat untreated past 72 hours. Cat 3 requires HAZWOPER-certified crews, full PPE, removal of all porous materials including drywall and insulation, antimicrobial treatment, and post-remediation clearance testing.

Per IICRC S500 timeline assumptions: Cat 1 water transitions to Cat 2 on contact with contaminated materials and is presumed Cat 2 by 24-48 hours regardless. Cat 2 transitions to Cat 3 within 48-72 hours of stagnation. This is why the IICRC 24-hour clock is critical — every hour of delayed mitigation increases the contamination category, the demolition scope, and the cost.

Category determines scope, PPE, salvageability of materials, and the protocols required for remediation. Insurance carriers expect (and most require) that documentation include the category determination, the IICRC S500 protocol followed, daily psychrometric readings, and a clearance moisture survey. Failing to categorize correctly — or failing to document the determination — is a primary reason claims get reduced or denied.

In Cat 1 events, drywall can typically be dried in place if action is fast. In Cat 2, drywall paper is contaminated and the lower 12-24 inches typically must be removed (a 'flood cut') with antimicrobial treatment of the remaining stud cavity. In Cat 3, all porous materials including the entire affected drywall must be removed — drying contaminated drywall is not an option per S500.

An IICRC-certified water damage technician on-site, using the source of water, condition of the affected space, and time elapsed since the loss began. DRR's certified field crews make the determination at the start of every job and document it as the first entry in the drying log — a defensible record your adjuster will accept.