Getting filtered water to a tap is a plumbing question with four common answers, and they differ in what they cost, what they require of the existing tap, and whether they survive a house move. Working out which is available to you takes about ten minutes with a cloth and a look inside the cabinet, and it settles the choice more decisively than any comparison of media.
On the spout: the faucet mounted filter
The simplest connection replaces the aerator with a small filter body that sits on the end of the spout, with a lever to switch between filtered and unfiltered. It is cheap, needs no tools beyond a cloth, and comes off in minutes. It requires a standard aerator thread, which many pull out sprays and designer taps do not have, so check by unscrewing the aerator first. The costs are appearance, a slower flow, and a small cartridge that runs down quickly if it is used for washing up as well as drinking.
Beside the sink: diverter to a countertop unit
A diverter valve fits where the aerator was and sends water through a hose to a unit on the bench, which returns treated water through its own small spout. This gives more media than a faucet mount, so better performance and longer cartridge life, while remaining fully removable. It needs the same aerator thread and it needs bench space. It is the usual answer for renters who want more than a spout filter and cannot alter the plumbing under the sink.
Under the sink, out of the existing tap
An inline cartridge plumbed into the cold supply treats everything that comes out of the existing cold tap, with nothing visible above the counter. It needs cabinet space, a tee into the cold feed and clearance to change cartridges. The compromise is that all the cold water is filtered, including what fills a washing up bowl, so the cartridge is consumed faster than a system feeding one dedicated tap. It suits households that want filtered water without a second faucet and without anything on show.
A dedicated faucet, and when it is required
The fourth option puts a separate small tap on the sink deck, fed from an under sink system. It is required for reverse osmosis, since RO water should not share a path with unfiltered hot water through the mixer, and it is the neatest arrangement for any system where you want to filter only what is drunk. It needs a spare knockout in the deck or a hole drilled through the worktop, which is easy in stainless and a specialist job in stone. Our whole house filter guide covers the alternative of treating everything at the main instead.
Questions people ask about water filter to tap
Can any tap take a faucet mounted filter?
Only one with a standard aerator thread. Unscrew the aerator and look before buying, since many pull out and designer taps have no usable thread.
Is an under sink filter better than a faucet mount?
It holds far more media, so it performs better and lasts longer, but it needs cabinet space, a tee into the cold feed and clearance for changes.
Do I need a separate tap?
For reverse osmosis, yes, so treated water never shares a path with unfiltered hot water. For a simple inline cartridge, no.
Which option suits a rental?
A faucet mount or a countertop unit on a diverter, since both attach at the aerator thread and remove without trace when you leave.