A water tap filter screws onto the end of the faucet and treats only the water you draw for drinking and cooking. It is the cheapest way to deal with chlorine taste, and the fastest to install, but the same small cartridge that makes it convenient is what limits how much it can do and how long it lasts.
How the unit works
Inside the housing is a compact carbon block, sometimes with an added media layer for lead or cysts. A lever or collar diverts water either through the block or straight out unfiltered, and that diverter matters more than people expect: filtered water is for drinking and cooking, unfiltered for rinsing dishes and filling the mop bucket, because sending every gallon through the cartridge burns it out in weeks. Carbon works by contact time, so the filtered setting deliberately restricts flow to a slower stream.
What it can and cannot treat
Carbon blocks are strong on chlorine taste and odor, many disinfection byproducts and a range of organic compounds, and certified models add lead and cyst reduction. They do not remove hardness, so scale and spotting continue exactly as before. They do not remove nitrate or dissolved salts, and they are not a disinfection step for water that has tested positive for bacteria. Before buying, look up your utility's Consumer Confidence Report: the EPA requires every community water system to publish one annually and maintains a finder for them, so you can aim the cartridge at what is actually in your supply.
Will it fit your faucet
Tap filters attach to the aerator threads at the spout tip. Unscrew your aerator and look: if you find male or female threads in a standard size, an adapter in the box will almost certainly match. If your faucet is a pull-down or pull-out sprayer, has a hidden aerator recessed behind a decorative ring, or is a single-piece designer spout with no removable insert, no tap filter will mount to it. Sink-mounted soap dispensers and shallow faucet-to-basin clearance also matter, since the housing adds length and can leave you unable to fit a tall pot under the spout.
Running one without frustration
Flush a new cartridge for the time the maker states, until the water runs clear of carbon fines. Never send hot water through it: heat strips the carbon and can warp the housing, so switch to bypass before you fill anything from the hot side. Expect the flow to drop as the block loads with sediment, and treat that drop as the real replacement signal rather than waiting for taste to come back. Keep the old aerator in a drawer, because you will want it if you ever remove the filter.
When to stop patching and go under the sink
If the diverter is a daily annoyance, if the housing wobbles the faucet, if you replace cartridges more often than you like, or if you want reverse osmosis rather than carbon, the answer is an under-sink system with its own small faucet. It costs more up front and needs a hole in the sink or worktop, but the cartridges are far bigger, the flow is normal, and nothing hangs off the spout. Our whole house filter guide covers the opposite move, treating everything at the main line instead.
Questions people ask about water tap filter
Does a water tap filter reduce water pressure?
It reduces the flow at that tap when the filtered setting is selected, because carbon needs contact time to work. House pressure elsewhere is unaffected.
Can I use a tap filter on hot water?
No. Hot water damages the carbon and can distort the housing, so switch the diverter to unfiltered before drawing anything hot.
Will a tap filter help with hard water?
No. It leaves calcium and magnesium in the water, so limescale in the kettle and spots on glassware will continue until you soften or condition the supply.
How long does a tap filter cartridge last?
Makers rate them in gallons, typically a few months of drinking and cooking use. Sediment-heavy water and using the filtered setting for everything both shorten that considerably.