Water damage glossary

A plain-English guide to the terms restoration crews and insurance adjusters use, from Category 3 water to flood cuts, curb valves and drain backup cover.

By the Water Damage Services Knoxville editorial team · Last reviewed October 14, 2026

What do restoration terms mean?

These are the words a restoration crew or an insurance adjuster is most likely to use during a water damage job. Each definition is written in plain language.

Air mover: A high-velocity fan aimed low across wet floors and walls. It speeds up evaporation from surfaces so dehumidifiers can pull the moisture out of the air.
Backwater valve: A one-way valve on a home's sewer line that lets wastewater leave but closes if sewage flows back from the public main. It helps keep a sewer surcharge from coming up through basement floor drains and fixtures.
Category 1 water: Clean water from a supply line, burst pipe or tub overfill. Under the IICRC S500 standard, most materials wet by Category 1 water can be dried in place if work starts quickly.
Category 2 water: Grey water with some contamination, such as discharge from a washing machine or dishwasher, or a toilet overflow without waste. Carpet pad is usually removed.
Category 3 water: Grossly contaminated water such as sewage and flood water from rivers, creeks or the street. Porous materials it touches are normally removed and replaced.
Condensate line: The small pipe that carries water from an air conditioner, heat pump or high-efficiency furnace to a drain. When it clogs, water can overflow the drain pan and soak ceilings, closets or attic floors without anyone noticing.
Crawl space encapsulation: Sealing a crawl space with a heavy plastic liner over the floor and up the walls, closing the vents and often adding a dehumidifier. It controls ground moisture after the space is dry. It is not a substitute for drying after water damage.
Curb valve: The shutoff valve in the water meter box near the street. It is owned by the water utility, which can close it if the main shutoff inside the house fails.
Dehumidifier: A machine that pulls water vapor out of the air. Restoration crews use large refrigerant or desiccant units sized to the wet area.
Extraction: Pulling standing water out of floors, carpet and pad with pumps, wands or weighted tools before drying equipment goes in. It is the fastest way to cut drying time.
Flood cut: A horizontal cut through drywall, usually 12 to 24 inches above the highest water mark, so wet insulation can come out and the wall cavity can dry.
Flood zone: An area FEMA maps by flood risk on its Flood Insurance Rate Maps. Lenders may require flood insurance in high-risk zones. Homes outside mapped zones can still flood from runoff, blocked drains and undersized pipes.
Hydrostatic pressure: The push of water held in saturated soil against a basement wall or floor. After heavy rain it can force water through cracks, joints and the seam where the wall meets the slab, even when no plumbing is leaking.
Main shutoff valve: The valve where the water line enters the house. Closing it stops water to every fixture. In East Tennessee homes it is often in the crawl space, basement or a utility closet.
Moisture mapping: Taking moisture readings across a wet room and recording them on a sketch or floor plan. It shows how far water spread under floors and inside walls, and it gives a record to compare against on each drying visit.
Moisture meter: A tool that reads the moisture content of drywall, wood and other materials. Drying is finished when readings match normal dry levels for that material.
Mold remediation: Removing mold growth and the materials it has damaged, then fixing the moisture that caused it. It usually involves containment to keep spores from spreading, cleaning or removing affected materials and drying the area.
NFIP: The National Flood Insurance Program, run by FEMA. It sells most residential flood policies in the US. Standard homeowners policies generally exclude flooding from surface water.
Sewer and drain backup endorsement: An add-on to a homeowners policy that covers water backing up through drains or a sump pump. Without it, many policies exclude this kind of damage.
Structural drying: Drying the building itself, such as framing, subfloors, drywall and wall cavities, rather than only the surfaces. Crews use dehumidifiers, air movers and moisture readings, and they often open walls so air can reach hidden water.
Subfloor: The wood layer under finished flooring. Water that runs under hardwood, laminate or vinyl soaks into it and can cause cupping, swelling and mold if it is not dried.
Sump pump: A pump set in a pit at the lowest point of a basement or crawl space. A float switch starts it when groundwater fills the pit, and it pumps the water out through a discharge line away from the house.
Thermal imaging camera: A camera that shows surface temperature differences. Wet areas often read cooler as water evaporates, so crews use it to find where water may have spread. A moisture meter confirms what the camera suggests.
Vapor barrier: A plastic sheet laid over the soil in a crawl space to stop ground moisture rising into the house. Torn or missing barriers are a common cause of crawl space dampness.
Water mitigation: The first stage of a water damage job: stopping the source, removing standing water and starting drying to limit further damage. Repairs and rebuilding that come afterward are usually called restoration.

Where do these definitions come from?

Water categories follow the IICRC S500 standard. Flood insurance terms follow FloodSmart.gov. Drying guidance follows the EPA's mold and moisture guide. For how these fit together on a real job, see emergency water damage restoration.