Most under-sink filters are within reach of a confident DIYer. The part that catches people out is rarely the filter — it is drilling the countertop for the dedicated tap.
What you are actually doing
Three connections: tapping into the cold water supply, mounting the filter housing inside the cabinet, and running a line to a dedicated faucet on the sink or counter. Some systems skip the third by connecting to your existing tap instead, which avoids drilling entirely.
Tools
Adjustable wrench, screwdriver, bucket and towels, plumber’s tape, and a drill with the correct bit if a new tap hole is needed. Stainless steel sinks take a standard hole saw. Granite, quartz and composite counters need a diamond bit and steady water cooling — and a cracked stone counter costs many times the filter.
The sequence
Shut off the cold supply under the sink and open the tap to release pressure. Fit the supply adapter to the cold line. Mount the housing on the cabinet wall, leaving clearance below to swap cartridges — this is the step people regret, because a housing mounted too low cannot be opened. Connect tubing, fit the dedicated faucet if using one, then open the supply slowly and check every joint.
Run the system for several minutes before drinking. New carbon cartridges release fine black dust, and the first few litres will look grey. That is normal and it clears.
Where it goes wrong
Overtightening plastic fittings cracks them — hand-tight plus a quarter turn is usually right. Push-fit tubing must be cut square and pushed fully home, or it will leak slowly and you will find out via a swollen cabinet floor weeks later. Check under the sink daily for the first week.
When to call a plumber
If your shut-off valves are seized, if the supply lines are corroded, if the counter is stone, or if you are on a rented property. An hour of a plumber’s time is cheaper than a flooded kitchen or a cracked worktop.
Under-sink systems → · Browse on Amazon.ca →
Disclosure: some links in this article are affiliate links. If you buy through them we may earn a commission at no extra cost to you.