Reference

Water Damage & Restoration Glossary

Plain-language definitions of the terms used across this reference — from IICRC S500 categories and classes to psychrometry and insurance endorsements. Each entry is an anchor you can link to directly.

Air mover #: A high-velocity fan used in structural drying to move air across wet surfaces, speeding evaporation. Placed at low angles to create a vortex of airflow around a room.
Black water Cat 3 #: IICRC S500 Category 3 water — grossly contaminated water that may contain pathogens, sewage, or toxins (e.g., sewage backups, rising river floodwater). Treated as a biohazard.
Category of water #: Under IICRC S500, the classification of water by its level of contamination at the source: Category 1 (clean/sanitary), Category 2 (significantly contaminated, "gray"), or Category 3 (grossly contaminated, "black").
Class of water #: Under IICRC S500, the classification of a loss by the amount of water and the rate of evaporation expected — Classes 1 through 4 — which drives how much drying equipment is needed.
Condition 1, 2, 3 (mold) S520 #: IICRC S520 mold conditions: Condition 1 is a normal fungal ecology; Condition 2 has settled spores/fragments; Condition 3 has actual mold growth. Remediation aims to return an area to Condition 1.
Containment #: Physical isolation of a mold or contamination work area — typically polyethylene barriers under negative air pressure — to prevent the spread of spores or contaminants to clean areas.
Dehumidifier (LGR / desiccant) #: Equipment that removes moisture from the air during drying. Low-grain refrigerant (LGR) units condense water vapor; desiccant units adsorb it with a drying medium, working well at lower temperatures and humidities.
Dew point #: The temperature at which air becomes saturated and water vapor condenses. A core psychrometric value used to judge condensation risk and drying conditions.
Grain depression GPP #: The difference in grains per pound (GPP) of moisture between the air entering a dehumidifier and the air leaving it — a measure of how effectively the unit is pulling moisture from the air.
Grains per pound GPP #: A unit of absolute humidity — the weight of water vapor (in grains) per pound of dry air. Restorers track GPP to confirm air is actually drying out.
Gray water Cat 2 #: IICRC S500 Category 2 water — water with significant contamination that could cause illness if contacted or ingested (e.g., washing-machine overflow, dishwasher discharge, toilet overflow with urine but no feces).
HEPA #: High-Efficiency Particulate Air filtration that captures at least 99.97% of particles 0.3 microns in size. Used in air scrubbers and vacuums during mold and contamination work.
IICRC #: The Institute of Inspection, Cleaning and Restoration Certification — the body that publishes the consensus standards for water restoration (S500) and mold remediation (S520).
Moisture content #: The amount of water in a material, often expressed as a percentage. Restorers compare wet materials to a dry standard (an unaffected reference area) to define a drying goal.
Negative air pressure #: A containment technique in which an air scrubber exhausts more air than enters a space, so air flows inward — preventing contaminated air from escaping the work area.
NFIP #: The National Flood Insurance Program, administered by FEMA, which provides flood insurance in participating communities. Standard homeowners policies exclude flood damage; NFIP or private flood coverage fills that gap.
Psychrometry #: The study of the physical properties of air–water-vapor mixtures (temperature, relative humidity, dew point, GPP). It is the scientific basis for how restorers control and verify drying.
Relative humidity RH #: The amount of water vapor in air expressed as a percentage of the maximum the air can hold at that temperature. Lowering RH accelerates evaporation from wet materials.
Restorable vs. non-restorable #: Whether a water-damaged material can be cleaned, dried, and returned to service (restorable) or must be removed and replaced (non-restorable) — a judgment driven by material type, water category, and exposure time.
S500 S500 #: The IICRC ANSI-accredited Standard for Professional Water Damage Restoration — the consensus document defining water categories, classes, and the restoration process.
S520 S520 #: The IICRC ANSI-accredited Standard for Professional Mold Remediation — defining mold conditions, containment, and remediation principles.
Water backup endorsement #: An add-on to a homeowners policy that covers damage from water or sewage backing up through drains or sump pumps — a peril typically excluded from base coverage and separate from flood insurance.

Sources

01IICRC — Standards (S500 / S520) — Source of category, class, and mold-condition definitions.
02EPA — Mold — Mold and moisture terminology.
03FloodSmart / NFIP — Flood-insurance terminology.

Definitions reviewed against IICRC S500/S520, EPA and NFIP terminology. · Last reviewed: June 12, 2026