Plumbing Terms, in Plain English
The vocabulary you meet on quotes, inspection reports and the parts aisle: what each term means, why it matters in your home, and what the work around it typically costs. Written for homeowners, reviewed against plumbing code and manufacturer documentation.
Water Pressure
The force that pushes water through your pipes and out of fixtures, measured in pounds per square inch (PSI) and ideally sitting between 40 and 60 PSI in a home.
Read definition →PSI (Pounds per Square Inch)
The standard unit for measuring water pressure, where residential plumbing typically targets 40 to 60 PSI and code limits incoming pressure to 80 PSI.
Read definition →Pressure Reducing Valve (PRV)
A spring-loaded valve installed on the main line that lowers high municipal pressure to a safe household level, usually preset around 50 PSI.
Read definition →Water Hammer
The banging or knocking in pipes that happens when fast-moving water is suddenly stopped by a closing valve, sending a shock wave back through the line.
Read definition →Main Shutoff Valve
The valve that stops all water entering the house, typically located where the supply line comes through the wall near the meter or in the basement.
Read definition →Water Meter
The utility-owned device that measures how much water your home uses, usually located at the property line in a buried box or in the basement.
Read definition →GPM (Gallons Per Minute)
A measure of flow rate, the volume of water a fixture or system delivers each minute, distinct from pressure, which is the force behind it.
Read definition →Angle Stop / Fixture Shutoff
The small individual shutoff valve under a sink or behind a toilet that stops water to that one fixture without shutting down the whole house.
Read definition →Anode Rod
A sacrificial metal rod inside a tank water heater that corrodes in place of the steel tank, protecting it from rust for as long as the rod lasts.
Read definition →Tankless Water Heater
A water heater that heats water on demand as it flows through, rather than storing a tank of hot water, giving endless hot water and a smaller footprint.
Read definition →T&P Relief Valve (TPR)
A safety valve on every tank water heater that releases water if temperature or pressure climbs too high, preventing the tank from rupturing or exploding.
Read definition →Dip Tube
A long tube inside a tank water heater that delivers incoming cold water to the bottom of the tank, so it heats before rising to the hot outlet at the top.
Read definition →Recovery Rate / First-Hour Rating
Two related capacity measures: recovery rate is how fast a heater reheats water, and first-hour rating is how much hot water it can deliver in the first hour of heavy use.
Read definition →Thermal Expansion Tank
A small tank that absorbs the pressure increase created when water heats and expands in a closed plumbing system, protecting the water heater and valves.
Read definition →Sediment (Water Heater)
The mineral and scale buildup that settles at the bottom of a tank water heater over time, reducing efficiency and causing popping or rumbling noises.
Read definition →Heat Pump Water Heater
A high-efficiency electric water heater that moves heat from the surrounding air into the tank instead of generating it directly, cutting energy use by 60 to 70 percent.
Read definition →P-Trap
The U-shaped bend of pipe under every sink, tub and shower that holds a small pool of water to block sewer gas from rising into the room.
Read definition →S-Trap
An older S-shaped trap configuration, now banned by code, that can siphon its own water seal dry and let sewer gas into the room.
Read definition →Vent Stack / Plumbing Vent
The vertical pipe that runs up through the roof to let air into the drain system, so waste flows freely and trap seals are not siphoned away.
Read definition →Air Admittance Valve (AAV)
A one-way valve that lets air into a drain when needed but stays sealed otherwise, providing venting for a fixture without running a pipe to the roof.
Read definition →Cleanout
A capped access point on a drain or sewer line that lets a plumber insert a snake or camera directly into the pipe to clear clogs or inspect it.
Read definition →Trap Seal
The small pool of standing water held in a P-trap that physically blocks sewer gas from passing up through a fixture into the home.
Read definition →Branch Drain
A horizontal drain line that carries waste from one or more fixtures over to the main vertical stack, sitting between the fixture trap and the soil stack.
Read definition →Soil Stack
The main vertical drain pipe that collects waste from every fixture branch and carries it down to the sewer, extending up through the roof as the vent.
Read definition →Drum Trap
An older cylindrical trap, common under bathtubs in homes built before the 1970s, now outdated because it clogs easily and is hard to clean.
Read definition →PEX (Cross-Linked Polyethylene)
PEX is flexible plastic water-supply tubing that bends around corners and runs in long lengths with few fittings, now the most common material for whole-house repipes.
Read definition →Copper Pipe
Copper pipe is rigid metal water-supply tubing joined by soldered or pressed fittings, prized for durability and a long service life but more labor-intensive and costly to install than plastic.
Read definition →CPVC
CPVC is a rigid cream-colored plastic pipe rated for hot water that joins with solvent cement, used for water supply as a lower-cost alternative to copper.
Read definition →Push-Fit Fitting (SharkBite)
A push-fit fitting is a no-tools connector that seals a pipe joint when you simply push the pipe in, working across copper, PEX, and CPVC, with SharkBite the most familiar brand name.
Read definition →Galvanized Pipe
Galvanized pipe is old steel water pipe coated in zinc that corrodes and clogs from the inside over decades, a common cause of low pressure and rusty water in pre-1970 homes.
Read definition →Polybutylene Pipe
Polybutylene is a gray flexible plastic supply pipe installed from the late 1970s to the mid-1990s that is prone to sudden failure and is now widely flagged by insurers and inspectors.
Read definition →Nominal Pipe Size
Nominal pipe size is the rounded label name for a pipe diameter, such as half-inch or three-quarter-inch, which rarely matches the pipe’s actual measured dimensions.
Read definition →Dielectric Union
A dielectric union is a coupling with a non-conductive separator that joins two different metals, such as copper and steel, to stop the galvanic corrosion that would otherwise eat the joint.
Read definition →Slip-Joint Connection
A slip-joint connection seals a drain pipe with a beveled nylon washer compressed by a hand-tightened nut, the take-apart joint used on sink traps and tailpieces.
Read definition →Wax Ring
A wax ring is the soft sealing gasket that sits between a toilet base and the floor flange, blocking water and sewer gas from escaping at the connection.
Read definition →Toilet Flange / Closet Flange
A toilet flange, or closet flange, is the ring that anchors a toilet to the floor and connects it to the drain pipe below, holding the bolts that clamp the bowl down.
Read definition →Fill Valve (Ballcock)
A fill valve, the modern replacement for the old ballcock, is the tank part that refills a toilet after a flush and shuts off when the water reaches the set level.
Read definition →Flapper
A flapper is the hinged rubber seal at the bottom of a toilet tank that lifts to release water into the bowl on a flush, then drops back to hold the tank full.
Read definition →Faucet Cartridge
A faucet cartridge is the replaceable inner valve that controls water flow and temperature in a modern single- or double-handle faucet, and the usual cause of a drip.
Read definition →Aerator
An aerator is the small screened tip that screws onto a faucet spout, mixing air into the stream to soften the flow, cut splashing, and save water.
Read definition →Sillcock / Hose Bib
A sillcock, or hose bib, is the outdoor faucet on the side of a house where a garden hose connects, with frost-proof versions designed to resist freezing.
Read definition →Pressure-Balancing / Mixing Valve
A mixing valve blends hot and cold water to a set temperature, and the pressure-balancing version protects a shower from scalding when water is drawn elsewhere in the house.
Read definition →Sewer Lateral
A sewer lateral is the underground pipe that carries wastewater from a house to the public main or septic tank, and on most properties it is the homeowner’s responsibility.
Read definition →Drain Field / Leach Field
A drain field, or leach field, is the network of buried perforated pipes and gravel that releases treated septic effluent into the soil for final filtering.
Read definition →Septic Tank
A septic tank is the buried watertight container that holds household wastewater long enough for solids to settle out before the liquid flows to the drain field.
Read definition →Hydro Jetting
Hydro jetting clears a drain or sewer line by blasting high-pressure water through a special nozzle, scouring the pipe walls clean rather than just punching a hole through a clog.
Read definition →CIPP / Pipe Lining
CIPP, or cured-in-place pipe lining, is a trenchless repair that pulls a resin-soaked liner into a damaged sewer pipe and hardens it into a new pipe inside the old one.
Read definition →Backwater Valve
A backwater valve is a one-way gate installed in a sewer line that lets wastewater flow out but slams shut to stop sewage from flooding back into the house.
Read definition →Effluent
Effluent is the clarified liquid wastewater that flows out of a septic tank to the drain field after the solids have settled and floated out of it.
Read definition →Septic Baffle
A septic baffle is a wall or pipe at a tank’s inlet and outlet that directs flow and keeps the floating scum layer from escaping toward the drain field.
Read definition →Root Intrusion
Root intrusion is the growth of tree and shrub roots into a sewer or drain pipe through cracks and joints, drawn by the water inside, where they snag waste and cause backups.
Read definition →Sump Pump
A sump pump is a pump set in a basin (the sump pit) at the low point of a basement or crawl space that automatically removes groundwater before it floods the floor.
Read definition →Sewage Ejector Pump
A sewage ejector pump lifts wastewater and solids from a below-grade bathroom or laundry up to the main sewer or septic line when gravity drainage is not possible.
Read definition →Well Pump (Submersible & Jet)
A well pump is the motorized pump that draws water from a private well and pushes it into the home’s plumbing, either lowered deep inside the well casing or mounted above ground.
Read definition →Well Pressure Tank
A well pressure tank stores pressurized water and a cushion of air so the well pump does not have to switch on every time a faucet is opened.
Read definition →Check Valve
A check valve is a one-way valve that lets water flow in a single direction and blocks it from running backward.
Read definition →Float Switch
A float switch is the level sensor that turns a sump or ejector pump on as water rises and off as it drains, using a buoyant float that moves with the water.
Read definition →Grinder Pump
A grinder pump shreds household waste into a slurry and pumps it under pressure to a sewer or septic line, used where the distance or uphill run is too much for a standard ejector pump.
Read definition →Water Softener
A water softener is a whole-house unit that removes the calcium and magnesium that make water hard, exchanging them for sodium so the water stops leaving scale and soap scum.
Read definition →Ion Exchange
Ion exchange is the process behind a water softener, where resin beads swap the calcium and magnesium ions in hard water for sodium or potassium ions.
Read definition →Reverse Osmosis (RO)
Reverse osmosis is a filtration method that forces water through a fine semipermeable membrane to strip out dissolved salts, minerals, and most contaminants, producing very pure drinking water.
Read definition →Hard Water / Grains Per Gallon
Hard water is water high in dissolved calcium and magnesium, measured in grains per gallon (gpg), where higher numbers mean more scale, more soap scum, and faster appliance wear.
Read definition →Sediment Filter
A sediment filter is a mechanical filter that strains out sand, rust, silt, and other suspended particles before they reach fixtures or downstream treatment equipment.
Read definition →Backwash (Filtration)
Backwash is a self-cleaning cycle in which water flows backward through a filter or softener media bed to lift out trapped dirt and flush it to drain.
Read definition →Salt Bridge
A salt bridge is a hard crust that forms across the salt in a softener’s brine tank, leaving an air gap below it so the salt no longer dissolves into the water and regeneration fails.
Read definition →Plumbing Code (UPC / IPC)
The plumbing code is the set of legal rules that govern how plumbing must be installed, drawn mainly from the Uniform Plumbing Code (UPC) or the International Plumbing Code (IPC) and adopted with local amendments.
Read definition →Plumbing Permit
A plumbing permit is official authorization from a local building department to perform plumbing work, paired with one or more inspections to confirm the work meets code.
Read definition →Rough-In Plumbing
Rough-in plumbing is the stage where all the supply and drain pipes are run inside walls and floors but no fixtures are connected yet, completed before the walls are closed up.
Read definition →Backflow Preventer
A backflow preventer is a device that keeps water from flowing backward through the plumbing, protecting the clean supply from contamination if pressure drops or reverses.
Read definition →Cross-Connection
A cross-connection is any point where the clean drinking water supply can come into contact with a non-potable source, creating a path for contamination to enter the potable system.
Read definition →Fixture Unit (DFU)
A fixture unit is a code unit of measure that rates how much water a fixture supplies or drains, letting designers size pipes and vents for the combined demand of a building.
Read definition →Wet Vent
A wet vent is a code-approved arrangement where a single pipe serves as both the drain for one fixture and the vent for another, reducing the number of separate vent lines needed.
Read definition →Licensed Plumber (Journeyman & Master)
A licensed plumber is a tradesperson who has met state or local requirements to perform plumbing work legally, typically ranked as a journeyman who works independently or a master who can design systems and pull permits.
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