Choosing and fitting an under-sink water filter in the kitchen

Is a simple inline filter enough

An inline filter is a single cartridge, usually the size of a large torch, spliced directly into the cold feed that already runs to your kitchen tap. It removes chlorine taste, sediment and some of the finer particles that make water look cloudy after works on the street main. It uses your existing tap, so there is no new hole to drill and no second spout on the worktop.

This is the right choice if your main complaint is taste or a faint chlorine smell rather than hardness or heavy sediment, and if you would rather not add a second tap to a worktop that is already crowded. It is also the cheaper route, both to buy and to maintain, since there is only one cartridge to replace.

It will not soften water or strip out dissolved minerals, so if your kettle scales up quickly or you are on a well outside the district heating network, an inline filter treats the symptom, not the cause.

When a multi-stage system with a separate tap makes sense

A multi-stage system runs the water through several cartridges in sequence, typically sediment, carbon and sometimes a fine membrane stage, before it comes out through a dedicated small tap fitted next to your main mixer. Because the filtered water only ever comes out of that separate tap, you can be confident that what you are drinking has actually gone through the full process, unlike an inline filter where the same spout carries both filtered and washing-up water.

It is worth the extra complexity if your water tastes noticeably of iron or sulphur, if you are filling a kettle or a baby's bottle daily and want a consistent result, or if you simply prefer having a distinct drinking tap so nobody runs the dishwasher through filtered water by mistake.

The trade-off is real: more cartridges to track and replace, a hole to drill in the worktop or sink for the new tap, and noticeably more space needed in the cabinet below.

How much space you actually need under the sink

An inline filter needs surprisingly little: about 30 cm of clear pipe run and enough depth to turn a cartridge by hand when it is due for changing. Most kitchen cabinets manage this even with a bin or a cleaning caddy already in there, as long as the filter housing itself does not sit directly behind the door hinge.

A multi-stage system is a different matter. Three cartridge housings mounted on a bracket, plus the tubing between them and the tap riser going up through the worktop, typically want a clear width of 35–40 cm and the full depth of the cabinet. If your under-sink space already holds a waste bin, a water softener unit or angle valves with awkward clearances, measure before you buy rather than after.

In both cases, leave enough slack in the tubing that you can pull a cartridge forward without disconnecting anything else, since that is exactly what you will be doing every few months.

Connecting the filter to the cold water supply

Both filter types tee into the cold feed after the angle valve, using a push-fit or compression T-fitting depending on what pipe you have. In older buildings with copper or the original steel branch pipe, a compression fitting with an olive is the more reliable route; in newer flats with PEX or multilayer pipe, a quality push-fit connector is usually sufficient.

For a multi-stage system, you also need to route the drinking tap's riser pipe up through a hole in the worktop or through the sink's existing tap hole if there is a spare one, and secure the tap body from underneath. This is the step that most often goes wrong for people doing it themselves — a riser pulled too tight, or a hole drilled slightly off, can leave the new tap wobbling or leaking at the base.

Always shut off the angle valve before you cut into the supply, and check every joint under pressure for at least ten minutes before you close the cabinet door and call it done.

Cartridge changes and everyday upkeep

Cartridge life depends on your water and how much you use the tap, but as a rule of thumb sediment and carbon cartridges want replacing every three to six months, and any membrane stage in a multi-stage system typically lasts longer but should still be checked on the same schedule. Most housings are sold with the change interval printed on the cartridge itself, which is worth writing on the cabinet door with a marker so you are not guessing a year later.

A drop in water pressure at the filtered tap is usually the first sign a cartridge is due, well before taste changes. Left too long, a clogged cartridge can also start growing bacteria rather than removing them, so treat the interval as a limit, not a suggestion.

Keep a spare set of cartridges in the cabinet so a change takes five minutes rather than a trip to the shop with the water shut off in the meantime.

• Note the cartridge change date on the housing or the cabinet door
• Keep a spare cartridge set on hand so changes take minutes, not a shopping trip
• Watch for dropping pressure at the filtered tap as the first sign of a clogged cartridge
• Check all joints for weeping after every cartridge change, not just at first install
• Shut the angle valve fully before opening any housing

Fitting it yourself or calling a plumber

An inline filter is a reasonable DIY job if you are comfortable turning off an angle valve, cutting a pipe cleanly and tightening a compression fitting without overdoing it. Most kits come with clear instructions and the fittings needed for standard Estonian pipe sizes, and the whole job takes under an hour.

A multi-stage system with a new tap is a bigger step up, mainly because of the worktop or sink hole and the extra joints that each need to be leak-tight under daily pressure. If you are not confident drilling into a stone or composite worktop, or if your existing angle valves are old and seize when you try to turn them, that is where it is worth booking a plumber rather than risking a cracked worktop or a valve that will not fully shut.

We fit both inline and multi-stage filters as plumbing work from 45 € per hour, and if the job also needs a new kitchen mixer tap to make room for a filtered spout, tap replacement is priced from 55 € per job. Either way you get a clean, tested installation and our 24-month guarantee on the work.