A water filter for faucet duty screws onto the end of your kitchen tap in place of the aerator and diverts water through a small carbon cartridge when you flip a lever. It is the cheapest way to get filtered water at the sink and the easiest to install, and its limits come almost entirely from how little filter media fits in something that small.
Will it fit your faucet?
This is the question that sinks most purchases. Faucet filters attach to the aerator threads, and they only fit standard male or female aerator threads on a conventional spout. Pull-down and pull-out sprayer faucets, spray-head faucets, square or oversized spouts and many European fittings simply have nowhere to attach, and no adapter in the box will change that. Unscrew your aerator before ordering and look at what is underneath. If your faucet cannot take a mount, the alternatives are a countertop unit that connects by a diverter hose, or an under-sink filter plumbed to its own small dedicated faucet.
What a small cartridge can and cannot do
Carbon in a faucet filter reliably improves taste and odor by removing chlorine, and better cartridges carry certified reduction claims for lead, certain pesticides and some other contaminants. Read the maker's performance data sheet rather than the box, because the specific contaminants a cartridge is certified for are listed there. What it cannot do is anything requiring a membrane or a large bed of media: it will not remove fluoride, nitrate, arsenic or dissolved solids, it will not soften water, and it is not a disinfection device, so it should never be used to make unsafe water safe. Vendor countertop and faucet-connected ranges publish cartridge life and flow ratings for exactly this comparison.
Flow, pressure and cartridge life
Filtered flow through a faucet mount is noticeably slower than the unfiltered tap, because contact time is what makes the carbon work. That is normal and expected. Most units let you switch back to unfiltered for filling pots and washing dishes, which also stretches cartridge life considerably. The cartridge is rated in gallons, and households almost always overrun it because it is easy to forget. A spent cartridge does not warn you, it just stops removing anything, so use the built-in indicator if there is one and set a reminder if there is not. Changing on schedule also avoids bacterial growth in an exhausted bed.
When to skip the faucet mount
If your sink is busy, if the filtered flow annoys you, or if you want more than taste improvement, spend a little more and go under the sink. An under-sink filter holds several times the media, runs at a usable flow, hides in the cabinet and takes far fewer cartridge changes per year. If you need dissolved contaminants gone, only reverse osmosis will do it, and that also lives under the sink. Faucet mounts remain the right answer for renters, for a second bathroom, and for anyone who wants better tasting water this afternoon with a wrench and five minutes. Our best faucet water filter guide compares the units that actually fit common faucets.
Questions people ask about water filter for faucet
Will a faucet filter fit a pull-down sprayer tap?
Almost never. Sprayer heads have no aerator threads to mount onto. A countertop unit with a diverter hose or an under-sink filter is the practical alternative.
Does a faucet filter remove lead?
Some do and many do not. Check the maker's certified performance data sheet for a lead reduction claim rather than assuming, since carbon alone does not guarantee it.
Why is the filtered flow so slow?
Contact time is what makes carbon work, so the cartridge deliberately restricts flow. Switch to unfiltered for pot filling and dishes, which also makes the cartridge last longer.
How often should I change the cartridge?
Follow the gallon rating, not the calendar, and err early in a busy household. An exhausted cartridge stops removing anything and gives no visible warning that it has.