Can I install an under-sink water filter myself?

Yes — most under-sink filters are designed for DIY installation in about an hour, using push-fit fittings and a T-adapter that taps the existing cold-water supply. A simple inline filter that feeds your existing faucet needs no drilling at all. A system with its own dedicated drinking-water faucet requires drilling a hole in the sink or countertop for the spout, which is the only step that intimidates some homeowners. Neither requires a plumber or a permit for a standard single-cartridge or multi-stage under-sink unit.

Where does an under-sink filter connect?

To the cold-water supply line under the sink. You close the cold shutoff, disconnect the cold supply line, and install the included T-fitting or saddle-style adapter between the shutoff and the faucet (or the cold line), then run tubing from that tap into the filter's inlet and from the outlet to either your faucet or a dedicated spout. Always tap the cold side — filters are rated for cold water and hot water can damage the cartridge and housing. Look for the IN and OUT arrows on the filter to get the flow direction right.

Do I need to drill a hole for an under-sink water filter?

Only if the system has its own dedicated filtered-water faucet. Inline systems that filter the water going to your existing kitchen faucet need no drilling. Dedicated-faucet systems require a hole in the sink deck or countertop — many stainless sinks have a knockout or an unused sprayer hole you can use, avoiding drilling entirely. If you must drill, a stainless sink takes a step bit and a granite or quartz counter needs a diamond hole saw and is the point at which some homeowners hire help.

Why is my under-sink water filter leaking?

Usually a push-fit tube not fully seated or a threaded connection missing its washer or tape. With push-fit (quick-connect) fittings, the tube must be pushed in firmly until it bottoms out — a tube that looks connected but is not fully seated will slowly weep or blow off under pressure. For threaded connections, confirm the rubber washer is present or the threads are taped. Turn the water back on slowly and inspect every joint; also make sure you did not reverse the IN and OUT ports on the filter head.

How often do I change an under-sink filter cartridge?

Most cartridges last 6 to 12 months, but it depends on your water quality and usage — a sediment-heavy supply or a large household shortens the interval. The manufacturer states a gallon rating and a time interval; go by whichever comes first. Signs a cartridge is spent are reduced flow, a return of taste or odor, or simply reaching the date. When you change a cartridge, run several gallons through the new one before drinking to flush out carbon fines, and sanitize the housing periodically.

How to Install an Under-Sink Water Filter: DIY Guide

Written & researched by Priya Anand DIY & Tools Editor

Updated August 2026

Close-up detail of the material being worked in a diy plumbing project, in warm evening lamplight

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Installing an under-sink water filter is an achievable DIY job — about an hour, $60 to $300 for the system, no permit and usually no plumber. You mount the filter housing inside the cabinet, tap the cold-water supply with an included T-fitting, and run tubing to the filter and out to your faucet or a dedicated spout. Push-fit connections make it tool-light. The only step that gives some homeowners pause is drilling a hole for a dedicated faucet — and many sinks have an unused knockout that avoids it.

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How to Install an Under-Sink Water Filter — This Old House

Tools and materials

The filter system with its T-adapter, tubing and mounting bracket.
An adjustable wrench, a drill and step bit or hole saw (only if drilling for a dedicated faucet), and PTFE tape.
A bucket, towels, and a marker for cutting tubing to length.
Basic hand tools — see best plumbing tools.

Close-up detail of the material being worked in a diy plumbing project, in warm late-afternoon light

Step 1: Plan the layout and shut off the cold water

Decide where the housing will hang inside the cabinet — leave clearance below it to unscrew the cartridge later. Close the cold shutoff valve under the sink and open the faucet to relieve pressure. Put a towel and bucket underneath, since the cold line still holds water.

Step 2: Install the T-adapter on the cold line

Disconnect the cold-water supply line at the shutoff or the faucet inlet. Thread the included T-fitting into the connection — this taps a branch off the cold supply for the filter. Use PTFE tape on threaded joints and confirm any rubber washers are in place. Reconnect the original supply line to the T so your faucet still gets water.

Golden-hour view of a person's hands tightening a fitting under a kitchen sink with a wrench

Step 3: Mount the filter housing

Screw the mounting bracket to the inside wall of the cabinet at a height that leaves room to remove the cartridge below. Note the IN and OUT arrows on the filter head — getting the flow direction wrong sends water backward through the cartridge and it will not filter properly. Hang the housing on the bracket.

Step 4: Run the tubing

Cut the supplied tubing to length with a clean square cut. Push each tube fully into its push-fit fitting until it bottoms out and you feel it seat — a partially seated tube is the main cause of leaks. Run one tube from the T-adapter to the filter IN port, and another from the OUT port to either your faucet inlet or a dedicated spout. If installing a dedicated faucet, mount it in an existing sink knockout or drill a hole with the appropriate bit.

Step 5: Turn on the water, flush, and test

Open the cold shutoff slowly. Watch every fitting for leaks — the T-adapter, both filter ports, and each push-fit joint. Then run the filtered water for several minutes (or the gallons the maker specifies) to flush carbon fines and air from the new cartridge before you drink it. Re-check all connections after the system has been under pressure for a few minutes.

Common mistakes

Push-fit tubing not fully seated, which weeps or blows off — the top cause of leaks.
Reversing the IN and OUT ports, so the filter does not work.
Tapping the hot line instead of cold, which damages the cartridge.
Not flushing the new cartridge before drinking, leaving grey carbon water.

When to call a pro

This is DIY for most people, with no permit for a standard filter. Consider hiring help if you need to drill a dedicated-faucet hole through a granite or quartz countertop (a diamond hole saw and a mistake is expensive), if you are installing a reverse-osmosis system that also needs a drain-line saddle connection, or if the existing shutoff valve is seized. A drain saddle for RO systems ties into the sink drain and, in some jurisdictions, has code requirements worth checking.

How to Install an Under-Sink Water Filter