Gateway/Water damage and mold glossary

Water damage and mold glossary

Plain definitions of the water damage, mold and insurance terms you will hear during a restoration job, with links to the Gateway services where each one comes up.

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Last updated October 23, 2026. Definitions follow the IICRC standards and common insurance usage. Your policy wording and the conditions at your property decide how they apply to you.

Jump to: Water categories and classes · Extraction and drying · Mold · Insurance and documentation

Water categories and classes

Category 1 water (clean water)

Water from a sanitary source that poses no substantial risk from skin contact, ingestion or inhalation, such as a broken supply line or an overflowing sink with no contaminants. The IICRC S500 standard notes that Category 1 water can degrade to Category 2 or 3 with time, warmth and contact with contaminated materials, so the category depends on what the water has become, not only where it started.

Category 2 water (gray water)

Water with significant contamination that can cause discomfort or illness if people are exposed to it. Typical examples are washing machine or dishwasher discharge and a toilet overflow that contains urine but no feces. Category 2 water left in place can degrade to Category 3.

Category 3 water (black water)

Grossly contaminated water that can carry pathogens, such as sewage, toilet backflow from beyond the trap, and rising flood water from rivers or streams. Porous materials soaked by Category 3 water, such as carpet pad and saturated drywall, are generally removed rather than dried in place, and the people doing the work wear protective equipment.

Water damage classes (Class 1 to 4)

Classes describe how much evaporation a water loss demands, which drives how much drying equipment it needs. Under the IICRC S500 approach, Class 1 involves a small share of wet, porous surfaces in the affected area, Class 2 a moderate share and Class 3 the largest share, often with water that came from overhead. Class 4 covers water held deep in low-permeance materials such as hardwood, plaster, brick and concrete, which need specialized drying methods and more time.

IICRC S500

The ANSI/IICRC S500 Standard for Professional Water Damage Restoration, published by the Institute of Inspection, Cleaning and Restoration Certification. It sets out the procedures and precautions restorers follow to inspect, extract, dry and clean after a water loss, including the water categories and classes on this page. Gateway's owner, Jake Lusby, holds the IICRC Water Restoration Technician (WRT) and Applied Structural Drying (ASD) certifications, which are built on this standard.

Extraction and drying

Mitigation vs. restoration

Mitigation is the work that stops damage from spreading: stopping or containing the water, extracting it, removing materials that cannot be saved and drying the structure. Restoration returns the property to its condition before the loss, which can include replacing drywall, flooring and trim. Insurers often treat the two phases as separate line items, so it helps to know which phase an estimate covers.

Structural drying

Drying the building itself, including framing, subfloor, wall cavities and concrete, not just the surfaces you can see. It relies on a balance of air movement, dehumidification and temperature control, with moisture readings taken until materials reach their drying goal. IICRC Applied Structural Drying (ASD) is the certification for this work, and Gateway's owner holds it.

Moisture mapping

Measuring moisture across an affected area with moisture meters, guided by a thermal camera, and recording the readings on a sketch that shows where the wet boundary is. Gateway uses both on its jobs. Repeating the readings each day documents drying progress and shows why specific materials were removed, which is the record an insurance adjuster reviews.

Dry standard (drying goal)

The moisture reading of the same kind of material in an unaffected part of the building. Restorers use it as the target for wet materials: drying is finished when affected materials read at or near the dry standard, not when they feel dry to the touch.

Related: Water damage restoration

Equilibrium moisture content (EMC)

The moisture content at which a material stops gaining or losing moisture because it is in balance with the surrounding air. Drying equipment lowers the humidity of the air so that wet materials move toward a lower equilibrium and release their water.

LGR dehumidifier

A low grain refrigerant dehumidifier, built to keep pulling moisture out of the air at lower humidity levels than a standard refrigerant unit. LGR units are a common choice for structural drying because the air has to stay dry for wet materials to keep releasing moisture.

Air mover

A high-velocity fan aimed across wet surfaces to speed up evaporation. Air movers work together with dehumidifiers: moving air without removing the moisture it picks up only raises the humidity indoors.

Flood cut

Removing the lower section of wet or contaminated drywall in a straight line above the water line so the wall cavity can be dried, inspected and cleaned. It is common after Category 3 water or when the insulation inside the wall is saturated.

Secondary damage

Damage that develops after the original water event because water was not removed or dried quickly enough, such as swollen trim, cupped flooring, delaminating cabinets, odor and mold growth. Mold can begin to grow on wet materials within 24 to 48 hours, which is why extraction and drying start as soon as possible.

Hydrostatic pressure

The pressure that saturated soil and groundwater put on basement walls and floors. After heavy rain it can push water through cracks, the joint between the wall and the floor slab, and other gaps, a common cause of basement water that has nothing to do with plumbing.

Mold

IICRC S520

The ANSI/IICRC S520 Standard for Professional Mold Remediation. It describes how to assess mold contamination, set up containment, remove contaminated material and verify the result, and it defines the three mold conditions below.

Mold conditions 1, 2 and 3

Terms from the IICRC S520 standard. Condition 1 is normal fungal ecology, the mix of mold spores found in any healthy indoor environment. Condition 2 is an area contaminated with settled spores or fragments that came from somewhere else. Condition 3 is an area with actual mold growth. Remediation aims to return Condition 2 and 3 areas to Condition 1.

Mold remediation vs. mold removal

Mold spores are present in nearly all indoor and outdoor air, so no service can remove every spore. Remediation means removing mold growth and contaminated materials, cleaning the area and correcting the moisture problem that let mold grow, so the area returns to normal conditions. If the moisture source is not fixed, mold comes back.

Containment

Physical barriers, usually polyethylene sheeting with a sealed entry, that isolate a mold work area from the rest of the building so spores and dust disturbed during removal do not spread. Larger or more heavily contaminated areas call for more complete containment.

Negative air pressure

Exhausting more air out of a contained work area than flows into it, usually with a HEPA-filtered air machine, so that any air leaks flow into the containment instead of out into clean parts of the home.

HEPA filtration

High-efficiency particulate air filtration. A true HEPA filter captures at least 99.97 percent of particles 0.3 microns in diameter. In remediation it is used in air scrubbers, negative air machines and vacuums to capture spores and dust.

Related: Mold remediation

Surface sample

A sample taken from a material, usually with tape or a swab, to identify what is growing or has settled on it. Gateway collects mold samples itself, and Teklab, an independent laboratory in Collinsville, IL, analyzes them. Surface samples are $75 to $125 each.

Air sample (spore trap)

A measured volume of air drawn through a cassette that traps airborne particles, which a laboratory then counts and identifies. Results are usually compared with an outdoor sample taken at the same time, because outdoor air always contains mold spores. Gateway takes air samples as well as surface samples, and the independent laboratory analyzes both.

Clearance testing (post-remediation verification)

Checking a remediated area after the work is finished, by visual inspection and often by sampling, to confirm it has returned to normal conditions before containment comes down and rebuilding starts. Gateway offers independent clearance testing on request.

Antimicrobial

A product applied to surfaces to inhibit bacteria or mold growth, used according to its label after cleaning. An antimicrobial supports cleaning. It is not a substitute for removing contaminated material.

Insurance and documentation

Sudden and accidental vs. gradual damage

Many homeowners policies cover water damage from a sudden and accidental discharge, such as a burst supply line, but exclude damage from long-term seepage, repeated leaks or lack of maintenance. The insurer decides which applies under the policy wording. Dated photos and moisture readings help show what happened.

Sewer or water backup endorsement

An add-on to a homeowners policy that covers water backing up through sewers or drains, or overflowing from a sump. Standard homeowners policies often exclude this kind of loss unless the endorsement was purchased, and the endorsement usually has its own coverage limit.

Flood insurance

Separate coverage, often written through the National Flood Insurance Program, for damage from surface water that rises from outside, such as an overflowing river or flash flooding. Homeowners policies generally exclude this kind of flooding.

Xactimate

Estimating software, made by Verisk, that many insurers and adjusters use to price repair and restoration work line by line. A line-item scope that follows the same structure is easier for an adjuster to compare with their own estimate. Gateway writes its line-item scopes in Xactimate.

Proof of loss

A signed, often sworn, statement that a policyholder sends the insurer setting out the amount claimed and the facts of the loss. Policies set a deadline for it, so check your policy or ask the adjuster when it is due.

Public adjuster

A licensed adjuster hired by the policyholder, not the insurer, to prepare and negotiate a claim, usually for a percentage of the settlement. Gateway is a restoration contractor that documents damage for your claim. It does not act as a public adjuster, and your insurer decides coverage.

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