ARS WATER-DAMAGE RESOURCE CENTER

Water Damage and Structural Drying

Consumer and property-manager guidance on water source, contamination risk, affected materials, moisture measurement, and evidence-based drying.

Updated September 2026 · Technical review: ARS Restoration & Reconstruction

Before entering: treat standing water near electrical systems, sewage, floodwater, structural movement, and unknown contamination as unsafe. Leave the area and contact the appropriate emergency, utility, or qualified restoration professional.

Two classifications answer different questions

Water category

Category is about the water’s contamination and exposure risk. It can worsen with time, contact with materials, or movement through the building.

Understand Categories 1, 2, and 3 →

Water class

Class is about how much material is wet, how deeply moisture is held, and the expected evaporation load—not whether the water is sanitary.

Understand Classes 1 through 4 →

How professional structural drying works

Drying is a measured process, not simply leaving fans in a room. A qualified team typically:

Identifies safety concerns and helps coordinate correction of the water source.
Maps visible and hidden moisture with suitable instruments and documents baseline conditions.
Removes bulk water and evaluates materials for cleaning, controlled drying, or removal.
Creates an equipment and containment plan appropriate to the loss conditions.
Tracks temperature, relative humidity, vapor pressure relationships, and material moisture over time.
Adjusts equipment or access as readings show how the building is responding.
Documents drying goals and completion before reconstruction closes assemblies.

Read the homeowner’s guide to psychrometry and drying →

Useful questions before work begins

What is the known or suspected water source, and has it been stopped?
What category and class are being considered, and what observations support them?
Which areas and materials were tested, and were any areas inaccessible?
What materials are expected to dry in place, be cleaned, or be removed—and why?
How will moisture readings, equipment placement, daily conditions, and changes be documented?
What safety, containment, HVAC, asbestos, lead, or microbial considerations could change the plan?
What objective criteria will be used to decide that drying is complete?

Water is moving through the building now?

Stop the source only if it is safe. Photograph the affected areas, protect people from exposure, and get qualified help before hidden moisture spreads farther.

Sources, scope, and review

Review note: Prepared September 2026. The category, class, and drying explanations are plain-language summaries and do not reproduce the ANSI/IICRC S500. This resource is educational. It does not replace instructions from emergency services, building officials, medical professionals, your insurer, legal counsel, an engineer, or an environmental professional. ARS does not determine insurance coverage.