Plumbing & Leak Detection Glossary

Plumbing has its own vocabulary. These definitions are written for homeowners, not trades. Each term links to the service page or guide where it matters most. For help with a problem, start at our McLean plumber home page or browse our plumbing guides.

A

Acoustic leak detection

A method that uses sensitive ground and wall microphones to hear water escaping from a pressurized pipe, so the leak can be pinpointed before anything is opened. Learn more

Anode rod

A metal rod inside a tank water heater that corrodes on purpose so the steel tank does not. A worn-out rod is a common reason tanks start to rust and leak. Learn more

B

Backflow

Water flowing the wrong way in a plumbing system, which can pull dirty water into clean supply lines. Check valves and backflow preventers stop it. Learn more

Ball valve

A quarter-turn shutoff valve with a drilled ball inside. It is the most reliable type of main shutoff for a home. Learn more

Bucket test

A simple check that compares water loss in a bucket set on a pool step with water loss in the pool. If the pool drops faster, it likely has a leak. Learn more

Burst pipe

A pipe that splits or breaks open, often after freezing or from high pressure, and releases water quickly. Shut the main valve first. Learn more

C

Camera inspection

A waterproof video camera pushed through a drain or sewer line to show cracks, roots, sags and blockages on a screen. Learn more

Cast iron drain pipe

Heavy metal drain and sewer pipe used in many older homes. It can rust, crack and scale inside over time. Learn more

Check valve

A one-way valve that lets water flow in only one direction. Sump pumps and well systems use them to stop water from flowing back. Learn more

Cleanout

A capped opening on a drain or sewer line that gives a plumber direct access for cleaning or a camera. Learn more

Copper pipe (Type L and Type M)

Common water supply pipe. Type L has thicker walls than Type M, which matters when pinhole leaks start to appear. Learn more

Curb stop

A buried shutoff valve near the street or property line, usually operated by the water utility with a long key. Learn more

D

Dye test

A few drops of food coloring in a toilet tank. If color shows up in the bowl without flushing, the flapper is leaking. Learn more

E

Electronic leak detection

Leak finding that uses electronic listening, moisture and signal equipment instead of opening walls or floors to look. Learn more

Expansion tank

A small tank on the water heater supply that absorbs extra pressure when water heats and expands. Learn more

F

Fill valve

The toilet tank part that refills the tank after a flush and shuts off at the right water level. Learn more

Flapper

The rubber seal at the bottom of a toilet tank. A worn flapper lets water leak into the bowl and makes the toilet run. Learn more

Float switch

The switch that turns a sump pump on when water rises in the pit and off when it drops. Learn more

G

Galvanized pipe

Steel water pipe coated with zinc, common in homes built before the 1960s. It rusts from the inside and narrows over time. Learn more

H

Hydro jetting

Drain cleaning with a high-pressure water hose that scours grease, scale and roots from the inside of a pipe. Learn more

Hydrostatic pressure

Pressure from groundwater pushing against a basement floor or wall. It can push water up through cracks and joints. Learn more

I

Infrared thermal imaging

A camera that shows temperature differences. Hot-water leaks and wet spots often show up as warm or cool patches. Learn more

L

Lateral (sewer lateral)

The private sewer pipe that carries waste from your house to the public sewer main. Learn more

Leak indicator

The small triangle, star or dial on a water meter that spins with very low flow. Movement with all water off points to a leak. Learn more

M

Main shutoff valve

The valve that turns off water to the whole house. In McLean-area homes it is often in the basement where the water line enters. Learn more

Meter test

Shutting off every fixture and watching the water meter. If the meter or its leak indicator moves, water is escaping somewhere. Learn more

Moisture meter

A handheld tool that reads how wet drywall, wood or concrete is, used to map how far a leak has spread. Learn more

N

Non-invasive leak detection

Finding a leak with tools such as listening equipment, thermal cameras and tracer gas before cutting into walls, floors or yards. Learn more

P

PEX

Flexible plastic water pipe used in most new plumbing and repipes. It bends around corners and needs fewer joints. Learn more

Pinhole leak

A tiny hole in a copper pipe caused by corrosion from the inside. Where one appears, more often follow. Learn more

Pipe bursting

A trenchless method that pulls a new pipe through the old one while splitting the old pipe apart. Learn more

Pipe reroute

Abandoning a leaking pipe under a slab and running a new line through walls or ceilings instead. Learn more

Polybutylene pipe

Gray plastic water pipe used in many homes built from the late 1970s to the mid-1990s. It can fail without warning. Learn more

Pressure regulator (PRV)

A valve on the main water line that lowers street pressure to a safe level for household pipes and fixtures. Learn more

Pressure tank

The tank in a well system that stores water under pressure so the pump does not start every time a tap opens. Learn more

Pressure test

Isolating a section of pipe and watching a gauge. A falling reading confirms a leak in that section. Learn more

R

Root intrusion

Tree roots growing into a sewer line through cracks or joints, causing slow drains and backups. Learn more

S

Sediment

Minerals and debris that settle at the bottom of a water heater tank. It causes popping noises and wastes energy. Learn more

Service line

The underground water pipe that runs from the meter or street connection to your house. Learn more

Sewer backup

Wastewater flowing back into the home through floor drains or low fixtures because the line is blocked or broken. Learn more

Shower pan

The waterproof layer under a tiled shower floor. When it fails, water seeps into the floor or ceiling below. Learn more

Skimmer

The opening at the pool waterline that pulls surface water into the filter system. Its seams are a common leak point. Learn more

Slab leak

A leak in a water or drain pipe buried under a concrete floor, such as a basement slab or slab-on-grade addition. Learn more

Spot repair

Opening a small section of floor, wall or yard right at a leak and repairing only the damaged piece of pipe. Learn more

Sump pit (sump basin)

The lined hole in a basement floor where groundwater collects before the sump pump sends it outside. Learn more

T

Tankless water heater

A water heater that heats water as it flows instead of storing it in a tank. Learn more

Temperature and pressure relief valve (T&P valve)

A safety valve on a water heater that opens if the tank gets too hot or the pressure gets too high. Learn more

Thermal expansion

The growth in water volume as it heats. Without room to expand, pressure rises and can strain the heater and pipes. Learn more

Tracer gas

A safe gas mix pushed into a drained line. A detector finds where it escapes, which marks the leak. Learn more

Trenchless repair

Fixing or replacing a buried pipe through small access holes instead of digging a full trench. Learn more

W

Water hammer

A banging noise when a valve closes fast and the moving water slams to a stop. Over time it can loosen joints. Learn more

Wax ring

The seal between a toilet and the floor drain. A failed ring lets water leak at the base of the toilet. Learn more

Well pump

The pump that lifts water from a private well into the home. Most are submersible pumps down in the well. Learn more