Tap Buying Glossary | The Tap Guide

A

Aerator: The small mesh disc screwed into the end of a spout that mixes air into the water stream. It cuts down splashing and water use, and it's usually the first thing to clog with limescale in a hard water area.; Read our full guide on How to Clean Limescale From Taps.

B

Backflow prevention device: A fitting, most commonly a double check valve, that stops water being siphoned back into the mains supply. Required by law on any outdoor tap with a hose union fitting.; See our full guide to How to Protect Outdoor Taps From Freezing.
Bib tap: An outdoor tap with a threaded, downward-facing spout designed for attaching a hose. Almost every garden or garage tap in the UK is a bib tap of some kind.
Blanking plate: A flat cover, usually matched to the tap's finish, used to seal a spare tap hole in a sink, basin or worktop. Comes up most often when switching from a two or three hole setup to a single hole monobloc tap.
BSP thread: British Standard Pipe, the thread standard used on almost all UK tap connections and fittings. Most domestic taps use 1/2 inch BSP; larger bath fillers sometimes use 3/4 inch.

C

Cartridge: The general term for the mechanism inside a tap that controls flow and temperature. Could mean a traditional washer, the ceramic disc mechanism used in most modern mixers, or the thermostatic unit inside a shower valve.
Ceramic disc cartridge: A modern tap mechanism using two hard, precisely machined ceramic discs that slide against each other to control flow and temperature. Needs only a quarter turn or a short lever movement, and generally lasts far longer than a traditional washer.; More on this in our guide to What Is a Ceramic Disc Tap?.
Combi boiler: A boiler that heats water directly from the mains on demand, with no storage tank or cylinder. Hot and cold supplies usually run at similar, strong pressure, which suits most mixer taps well.; Our guide to What Flow Rate Do You Need From a Tap? covers this in full.
Concealed valve: A shower valve with its pipework hidden behind the wall, leaving only the controls and outlet visible. Gives a cleaner look than an exposed valve but needs more work to fit or repair, since the wall has to be opened up.

D

Deck mounted: A tap that sits directly on the basin, bath or worktop surround itself, rather than on the wall above it. The more common, generally simpler to fit option of the two.
Double check valve: See backflow prevention device. The specific fitting most commonly used to meet that requirement on outdoor taps.; Covered in more detail in our guide to How to Protect Outdoor Taps From Freezing.

E

Exposed valve: A shower valve with its pipework visible on the wall surface rather than hidden behind it. Quicker and cheaper to fit or service than a concealed valve, at the cost of a more traditional, less streamlined look.

F

Flow rate: How much water comes out of a tap over a set period, usually measured in litres per minute. Determined partly by the tap's own cartridge and any fitted restrictor, and partly by your home's actual water pressure.; Read our full guide on What Flow Rate Do You Need From a Tap?.
Frost-proof tap: An outdoor tap with its valve mechanism set back inside the warmer wall cavity, so the exposed outdoor section drains automatically when closed. Also called a self-draining tap.; See our full guide to How to Protect Outdoor Taps From Freezing.

G

Gravity fed system: A hot water system using a cold water tank in the loft to feed a hot water cylinder, relying on gravity rather than mains pressure. Hot water pressure is often noticeably weaker than mains-fed cold in these homes.; More on this in our guide to What Flow Rate Do You Need From a Tap?.

H

Headgear: The part of a traditional tap that the handle attaches to, and that unscrews to give access to the washer underneath. Usually undone with an adjustable spanner during a washer repair.; Our guide to How to Replace a Tap Washer covers this in full.

I

Isolation valve: A small quarter-turn valve fitted to a hot or cold supply pipe, usually just below a sink or basin, that lets you shut off water to a single tap without affecting the rest of the house.

L

Limescale: Calcium carbonate left behind when hard water evaporates or gets heated. Builds up on visible surfaces and inside aerators, cartridges and shower heads, and is worse in some parts of the UK than others depending on local geology.; Covered in more detail in our guide to How to Clean Limescale From Taps.

M

Mixer tap: Any tap that blends hot and cold water together before it comes out, whether through a single spout fed by one hole or two. The opposite of a separate tap set-up.; Read our full guide on How to Choose a Bathroom Tap.
Monobloc tap: A tap that fits through a single hole in a sink, basin or worktop, with hot and cold mixed inside one body before reaching a single spout. The standard choice in most modern kitchens and bathrooms.; See our full guide to How to Choose a Kitchen Tap.

O

O-ring: A small rubber ring seal used at various joints inside a tap, often around the spout base. When it wears, it's a common cause of a leak that persists after a washer or cartridge has already been replaced.; More on this in our guide to How to Fix a Dripping Tap.

P

Pillar tap: A traditional tap with separate hot and cold handles, each needing its own hole in the sink or basin. Also called a two hole (or three hole, with a spray) tap set-up.; Our guide to How to Choose a Bathroom Tap covers this in full.
PTFE tape: Thin, white plumber's tape wrapped clockwise around threaded pipe joints to help create a watertight seal. Cheap, and worth using on every threaded connection during a tap installation.
Pull-out spray: A kitchen tap spray head that detaches on a hose and pulls straight out toward you, retracting along roughly the same line. Sits lower and flatter than a pull-down tap, useful under a low cabinet or window.; Covered in more detail in our guide to Pull-Out vs Pull-Down Kitchen Taps.

S

Spout reach: How far a tap's spout extends horizontally over the sink or basin. Matters more than overall tap height for whether you can comfortably fill a pan or wash up without repositioning things.

T

Thermostatic valve: A valve that holds a set temperature steady automatically, even if pressure changes elsewhere in the house, such as someone flushing a loo while you're in the shower, a genuine safety feature rather than a luxury extra.
TMV (thermostatic mixing valve): A thermostatic valve tested and rated to a specific safety standard, TMV2 for domestic use or TMV3 for higher-risk settings like care homes. Worth checking for on any shower valve fitted for children or elderly relatives.

U

Unvented cylinder: A hot water system that stores water in a pressurised cylinder fed directly from the mains, with no loft tank needed. Gives strong, well matched hot and cold pressure, similar to a combi boiler.; Read our full guide on What Flow Rate Do You Need From a Tap?.

V

Valve seat: The fixed surface inside a traditional tap that a washer presses against to seal the flow shut. If the seat itself is pitted or scaled, a new washer alone won't stop a drip.; See our full guide to How to Replace a Tap Washer.

W

Wall mounted tap: A tap fitted above a basin or bath on the wall itself, rather than on the fixture. Gives a cleaner, more minimal look but needs pipework routed through the wall, best planned in during a full renovation.
Washer: A small rubber or fibre disc inside a traditional tap that compresses against the valve seat to seal the flow shut. Hardens and perishes with age, which is the most common cause of a dripping traditional tap.; More on this in our guide to How to Replace a Tap Washer.
Water hardness: How much dissolved calcium and magnesium your local water supply carries, picked up as rain filters through chalk and limestone. Much of the south east and Midlands has hard to very hard water; Scotland, Wales and the north west generally have it easier.; Our guide to How to Clean Limescale From Taps covers this in full.
WRAS approval: Confirmation that a tap or fitting meets the UK Water Supply (Water Fittings) Regulations, covering water safety and backflow prevention. Worth checking on the WRAS approved fittings directory before buying, particularly from marketplace sellers.; Covered in more detail in our guide to What Is a WRAS Approved Tap?.