Water Damage Restoration Glossary
Every term below is one you will meet on a wet job or in the water damage technician course — written the way a technician would explain it on site, not the way a textbook defines it. Each entry links to the page on this site that goes deeper. If you would rather drill them than read them, the same vocabulary is in the free WRT flashcards, and you can test yourself on the free practice test.
A
Absolute Humidity
The actual weight of water vapor in a given volume of air, independent of temperature. On a drying job it is tracked as grains per pound rather than as a percentage.
ACH (Air Changes per Hour)
How many times the air inside a contained space is replaced or filtered in an hour. It is the usual way to describe how hard an air filtration device is working in a containment.
Adsorption
Water vapor clinging to the surface of a material rather than soaking into it. Desiccant dehumidifiers work by adsorbing vapor onto a rotating wheel and then driving it off with heat.
Affected Material
Any building material or content that the water reached, whether it looks wet or not. Every affected material has to be found, documented and either dried or removed.
Air Mover
A high-velocity fan aimed across a wet surface to strip away the still, saturated layer of air sitting on it. Air movers speed up evaporation; they do not remove moisture from the building.
Airflow
Moving air across wet surfaces and through the drying chamber. Airflow is one leg of drying, alongside dehumidification and temperature control.
Ambient Conditions
The temperature and humidity of the air in a space at the time it is measured. Ambient readings inside, outside and in unaffected areas give the comparison a drying log needs.
Antimicrobial
A product applied to reduce or inhibit microbial growth on a surface. It is applied to cleaned surfaces, not used as a substitute for removing contamination.
Applied Structural Drying (ASD)
The IICRC certification that goes deeper into drying systems, equipment placement and psychrometric control than the water damage technician course does.
Assembly
A layered part of the building — a wall, floor or ceiling made of several materials fastened together. Water trapped between the layers of an assembly is why cavity drying exists.
B
Backflow
Water travelling the wrong way through a plumbing system and re-entering a building. Backflow from a sanitary line is treated as grossly contaminated water.
Biocide
A product intended to kill microorganisms on a surface. Killing growth does not remove it, so cleaning and removal still come first.
Black Water
The old trade name for grossly contaminated water — what is now called Category 3. Sewage, rising groundwater and seawater fall in this group.
Bound Water
Water held inside the structure of a material rather than sitting free in its pores. Bound water leaves slowly and is what makes dense materials take so long to dry.
Boundary Layer
The thin band of moist, still air resting directly against a wet surface. It stalls evaporation until airflow strips it away, which is the whole job of an air mover.
Building Envelope
The shell separating conditioned interior air from outdoor air. Whether the envelope is intact decides if an open or closed drying system makes sense.
C
Capillary Action
Water drawn through the tiny passages in a porous material, moving sideways and upward against gravity. It is why a wall is wet well above the visible water line.
Category 1 Water
Water from a clean source that is not expected to cause harm on contact. It can deteriorate to a dirtier category with time, temperature and what it touches.
Category 2 Water
Significantly contaminated water that could cause discomfort or sickness if someone contacted or swallowed it — appliance discharge, for example.
Category 3 Water
Grossly contaminated water that can carry disease-causing organisms or harmful agents, such as sewage or rising groundwater.
Category Deterioration
The slide from a cleaner category to a dirtier one caused by time, warmth and contact with soils or contaminants. Category is judged from the water as found, not only from where it started.
Category of Water
The classification of how contaminated the water is, from clean through grossly contaminated. Category drives cleaning, worker protection and what gets thrown away.
Cavity Drying
Pushing or pulling air through the space inside a wall, floor or ceiling assembly instead of opening it up. It saves materials when the contamination level allows it.
CEC (Continuing Education Credit)
Credits an IICRC certificant earns from approved activities to keep a certification current. Renewal requirements and fees are set by the IICRC.
Class 1 Water Damage
The smallest evaporation load: a small share of a room wet, with little moisture absorbed into porous materials.
Class 2 Water Damage
A significant evaporation load — an entire room of carpet and cushion wet, with water wicked up the walls.
Class 3 Water Damage
The greatest evaporation load, usually from water coming down from overhead so ceilings, walls, insulation and flooring are all wet.
Class 4 Water Damage
Deeply held water in materials that release it slowly — hardwood, plaster, concrete, brick and stone — calling for specialty drying methods and more time.
Class of Water Damage
The classification of how much evaporation load a loss presents — how much wet material there is and how hard it will be to dry. Class drives equipment counts, not cleaning.
Closed Drying System
A drying setup sealed off from outside air, where dehumidifiers handle all the moisture. It is the default when outdoor air is humid or the building is contaminated.
Condensation
Vapor turning back into liquid when it meets a surface colder than the dew point. Unchecked condensation is how drying creates damage in rooms the water never reached.
Containment
A sealed barrier that separates a work area from the rest of the building so contaminants and moisture do not spread. It is usually paired with air filtration and pressure control.
Contaminant
Anything in the water or in the building that could harm people or property — soils, chemicals, bacteria, mold. Contamination level is what separates the categories.
Controlled Demolition
Removing only the materials that cannot be cleaned or dried, in a planned way, rather than gutting a room. Every cut should be justified in the scope of work.
D
Daily Monitoring
Returning each day to record temperature, humidity and material moisture so you can prove the drying is progressing — or catch that it has stalled.
Dehumidification
Removing water vapor from the air so evaporation can continue. Without it, air movers simply move the same moisture from the materials into the room.
Delamination
Layers of a material separating after they get wet — carpet backing from face yarn, plies of engineered flooring. Delaminated material is usually unsalvageable.
Desiccant Dehumidifier
A dehumidifier that adsorbs vapor onto a chemical wheel and exhausts it, rather than condensing it on cold coils. It keeps working in cool air and can drive humidity very low.
Dew Point
The temperature at which air becomes saturated and moisture starts condensing. Any surface colder than the dew point will collect water.
Dry Bulb Temperature
Ordinary air temperature taken with a thermometer shielded from moisture — one of the two readings needed to plot air on a psychrometric chart.
Dry Standard
The moisture content of the same material, unaffected, in the same building. It is the benchmark a drying goal is set from rather than a fixed number.
Drying Chamber
The space you seal off and control as one drying environment. Sizing equipment to the chamber, not the whole house, is what keeps the numbers honest.
Drying Goal
The documented moisture content that affected materials have to reach, set from the dry standard. Drying is finished when the goal is met, not when the calendar says so.
Drying Log
The daily record of atmospheric and material readings for a job. It is the document that shows a third party the structure actually dried.
E
Engineering Controls
Physical measures such as containment, negative pressure and filtration used to keep contaminants away from people, rather than relying on protective gear alone.
Equilibrium Moisture Content
The moisture level a material settles at when it stops exchanging water with the surrounding air. Materials in the same room drift toward it at very different speeds.
Evaporation
Liquid water turning into vapor. It is driven by vapor pressure difference and helped along by airflow, heat and drier surrounding air.
Extraction
Physically removing liquid water with pumps, wands and weighted tools. Extraction pulls out far more water per hour than evaporation ever will, so it comes first.
F
Flood Cut
Cutting wall material a set distance above the water line to open the cavity for cleaning and drying. It is a removal decision, so contamination and material type drive it.
Free Water
Water sitting loose in the pores of a material or pooled on a surface. It leaves quickly with extraction and airflow, unlike bound water.
Fungi
Molds and related organisms that grow on damp organic material. Once growth is present, the job moves into remediation territory.
G
Grain Depression
The difference in grains per pound between the air going into a dehumidifier and the air coming out. It is the direct check on whether the unit is still doing useful work.
Grains Per Pound (GPP)
The weight of water vapor, in grains, carried by a pound of dry air. Falling GPP in the drying chamber means the dehumidification is winning.
Gray Water
The old trade name for significantly contaminated water, now called Category 2. Appliance discharge is the classic example.
H
Hardwood Floor Drying
Specialty drying of wood flooring using mats or panel systems that pull moisture through the boards. Wood holds water tightly, which is why these losses run long.
HEPA Air Filtration Device
A fan and high-efficiency filter used to scrub particles from the air in a contained work area, and to create pressure differences when ducted.
Humidity Ratio
The weight of water vapor per weight of dry air — the same idea as grains per pound, written as a decimal in engineering work.
Hygrometer
An instrument that reads relative humidity. Paired with a thermometer it becomes the thermo-hygrometer used for every atmospheric reading on a job.
Hygroscopic Material
A material that pulls moisture out of the air and gives it back as conditions change — paper, gypsum, textiles, wood. They keep a room humid long after the standing water is gone.
I
IICRC
The Institute of Inspection, Cleaning and Restoration Certification, the body that publishes the standards and issues restoration certifications. We are not affiliated with it.
In-Place Drying
Drying flooring and assemblies where they sit instead of removing them. It only makes sense when the water was clean enough and the materials can actually reach the goal.
Indoor Air Quality
The condition of the air people breathe in the building. Restoration work is supposed to leave it no worse than it was before the loss.
Initial Inspection
The first walk-through where you determine the category, map the affected areas and record the starting conditions. Everything in the scope of work traces back to it.
J
Job File
The complete record of a loss — readings, photographs, moisture maps, authorizations and the scope of work. It is what proves what was done and why.
L
Latent Heat
The heat absorbed when water evaporates and released when vapor condenses, without the temperature changing. It is why a drying room can feel cold while the air is doing work.
LGR Dehumidifier
A low grain refrigerant dehumidifier: a refrigerant unit that pre-cools incoming air so it can keep pulling water out of air that is already fairly dry.
Load Calculation
Working out how much dehumidification and airflow a chamber needs from its size and how wet it is, instead of guessing from the equipment on the truck.
M
Microbial Amplification
Existing microorganisms multiplying because the building stayed wet. Preventing it is the argument for drying quickly rather than thoroughly later.
Mitigation
The emergency phase that stops the loss getting worse: extraction, removal of unsalvageable material and drying. Rebuilding is a separate phase.
Moisture Content
How much water a material is holding, read with a moisture meter. It is only meaningful next to a dry standard reading from the same material type.
Moisture Map
A sketch of the affected areas with readings marked on it, updated as drying goes on. It shows migration a list of numbers cannot.
Moisture Meter
The instrument used to read moisture in materials, in penetrating and non-penetrating forms. Readings are compared against the dry standard, not against a universal number.
Mold
Fungal growth that appears on damp organic materials. Remediation of established growth is its own discipline with its own certification and standard.
Mold Growth Timeline
How quickly growth can begin once material stays wet, given the right temperature and food source. It is the reason response speed is treated as part of the work.
Monitoring
The ongoing readings taken through a drying job to confirm progress and adjust equipment. Without it, drying is a guess with a due date.
N
Negative Air Pressure
Keeping a contained work area at slightly lower pressure than the surrounding building so air flows in, not out, carrying contaminants with it.
Non-Penetrating Moisture Meter
A meter that reads moisture through a surface without making holes, useful for scanning quickly. It reads a shallow depth and can be fooled by metal or foil.
Non-Porous Material
A material water cannot soak into — glass, metal, hard plastics. Non-porous surfaces can usually be cleaned rather than removed, whatever the category.
O
Open Drying System
Using outdoor air as part of the drying, by ventilating the space. It only helps when the outside air is genuinely drier than the air inside.
Overdrying
Pushing materials below the dry standard, which can shrink, crack or split wood and finishes. Reaching the drying goal is the finish line.
P
Penetrating Moisture Meter
A meter with pins that measure resistance between them inside the material. It reads at depth and leaves small holes, so placement matters.
Permeance
How readily a material lets water vapor pass through it. Low-permeance layers trap moisture in an assembly and are the reason cavities need direct airflow.
Porosity
How much open pore space a material has, which decides how much water it can hold and how fast it releases it.
Porous Material
A material that absorbs water readily — carpet cushion, insulation, textiles. Once grossly contaminated water is involved, porous materials usually leave the building.
PPE
Personal protective equipment worn on a loss — gloves, eye protection, respiratory protection, suits. What is worn scales with the contamination present.
PPE Escalation
Increasing protection as the category or the work gets dirtier — for example moving up in respiratory protection when opening a contaminated assembly.
Pre-Existing Damage
Damage that was there before this loss. Photographing it at the initial inspection is what keeps it from becoming your problem later.
Pressure Differential
A deliberate difference in air pressure between two spaces, used to control which way air and contaminants travel.
Psychrometric Chart
The chart that ties dry bulb, wet bulb, dew point, relative humidity and grains per pound together, so any two readings give you the rest.
Psychrometry
The study of air and the moisture it carries. It is the science the whole drying side of the exam is built on.
R
Reference Reading
A reading taken in an unaffected area or outdoors for comparison. Without one, the numbers from the wet rooms mean very little.
Refrigerant Dehumidifier
A dehumidifier that condenses moisture on cold coils and drains it away. Conventional and LGR units both work this way; the LGR simply goes further.
Relative Humidity
The moisture in the air as a percentage of what that air could hold at its current temperature. It moves when the temperature moves, even if nothing was added or removed.
Remediation
Removing contamination and returning conditions to normal — the word used once microbial growth is involved rather than plain water.
Restorability
Whether a material can be cleaned and dried economically or has to be replaced. Category, material type and how long it stayed wet decide it.
S
S500 (ANSI/IICRC S500)
The consensus standard for professional water damage restoration, and the document the water damage technician exam is drawn from.
S520 (ANSI/IICRC S520)
The consensus standard for professional mold remediation — the companion document once growth, not just water, is the problem.
Saturation
Air holding all the vapor it can at its current temperature. Saturated air is at its dew point, and condensation begins on any cooler surface.
Scope of Work
The written plan of what will be cleaned, removed, dried and restored, and why. It is what the estimate, the authorization and the final invoice all hang on.
Secondary Damage
Damage caused by the moisture remaining after the initial event — swelling, staining, corrosion, microbial growth — rather than by the water itself.
Semi-Porous Material
A material that absorbs water slowly and gives it up slowly, such as wood, concrete or plaster. These are what turn a loss into a Class 4 drying problem.
Sewage
Waste water carrying human or animal waste. It is grossly contaminated water and is handled with containment, protection and heavy removal of porous materials.
Specific Humidity
The actual weight of moisture in the air regardless of its temperature, usually expressed in grains per pound. Unlike relative humidity, it does not move when you only change the heat.
Standing Water
Water still pooled on floors or in cavities. It is removed by extraction before any drying equipment goes in.
Structural Drying
Drying the building itself — framing, subfloors, wall assemblies — rather than only the surfaces you can see. Controlling airflow, humidity and temperature together is what makes it work.
T
Thermal Imaging Camera
A camera that shows surface temperature differences, which often reveal where moisture is. It finds suspect areas; a moisture meter confirms them.
Thermo-Hygrometer
The combined temperature and humidity instrument used to record chamber conditions, dehumidifier performance and outside air.
U
Unaffected Area
A part of the building the water never reached. It supplies the dry standard and the reference readings the rest of the job is measured against.
Unsalvageable Material
Material that cannot be cleaned or dried to a safe, usable condition and has to be removed. Contaminated porous material is the usual case.
V
Vapor Barrier
A low-permeance layer built into an assembly to stop vapor movement. It works against you during drying by holding water on one side.
Vapor Pressure
The pressure water vapor exerts in the air. Moisture always travels from higher vapor pressure to lower, which is what actually pulls water out of materials.
Vapor Pressure Differential
The gap in vapor pressure between a wet material and the air around it. Widen the gap and the material dries faster; close it and drying stops.
Ventilation
Exchanging inside air with outside air. Useful in an open drying system, harmful when the outdoor air is more humid than the air in the chamber.
W
Water Damage Restoration Certification
The general term people search for when they mean a restoration credential — most often the water damage technician certification, sometimes the drying certification alongside it.
Water Damage Restoration Technician (WRT)
The IICRC certification covering water damage work: categories and classes, psychrometry, drying and documentation. It is the certification this site prepares you for.
Water Migration
Water spreading from where it entered through gravity, capillary action and vapor movement. It is why the wet area is always larger than the visible one.
Water Restoration Vocabulary
The set of terms on this page. Working the same terms as a deck is usually faster than reading them, which is what the flashcards are for.
Wet Bulb Temperature
The temperature read by a thermometer with a wetted wick in moving air. The gap between wet bulb and dry bulb shows how much evaporation the air can still take.
Wicking
Water climbing a porous material against gravity — the reason drywall reads wet a foot or more above the water line.
WRT Certification
The credential earned by completing the water damage technician course and passing its exam. Course delivery, fees and renewal are set by the IICRC and the schools.
WRT Class
The instructor-led course, in person or by livestream, that precedes the exam. Upcoming sessions from the class feed are listed on this site.
WRT Exam
The certification exam that follows the course. Format questions are answered by the IICRC and the school; practice questions here are our own.
Try the free 20-question practice test — scenario questions on the topics the WRT exam covers, with an explanation after every answer.
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