How to Fit an Under-Sink Water Filter

Most under-sink water filters are designed for DIY installation — you do not need a plumber. With basic tools and around an hour of your time, you can have clean, filtered water flowing from your kitchen tap. This guide covers the general process; always follow the specific instructions included with your system.

What you will need

• Adjustable spanner or water pump pliers
• PTFE tape (thread seal tape)
• Bucket and towel
• Drill with a 12 mm bit (only if fitting a separate filter tap)
• The filter system and all included fittings

Step 1 — Turn off the water

Locate your mains stop valve — usually under the kitchen sink or where the mains enters your home. Turn it clockwise until it stops. Open the kitchen tap to drain the remaining water from the pipe and relieve pressure.

Step 2 — Choose your tap setup

Two options exist. If your system includes a separate filtered-water tap, you will drill a hole in your sink or worktop for it. If it filters your existing mains tap via a diverter valve, you connect the filter inline with the cold supply. Most Clarisink systems use a dedicated tap for the cleanest result.

Step 3 — Install the in-line valve

Disconnect the cold water feed to your tap. Install the supplied self-piercing saddle valve or push-fit tee connector onto the cold pipe. Wrap PTFE tape clockwise around any threaded connections to ensure a watertight seal. This tee splits your cold water: one feed to the tap as normal, one to the filter.

Step 4 — Mount the filter housing

Position the filter housing upright inside the cabinet, leaving enough space below to unscrew the cartridge for replacement — typically 10 cm of clearance. Screw the mounting bracket to the cabinet wall or side panel. Clip the filter onto the bracket.

Step 5 — Connect the tubing

Push the supplied flexible tubing from the tee valve into the filter inlet and from the filter outlet to the separate tap. Push-fit connectors click when seated — give each a gentle tug to confirm it is locked. Do not kink the tubing; route it neatly with the clips provided.

Step 6 — Turn on and check for leaks

Turn the mains stop valve back on slowly. Open the filtered tap and let water run for five minutes to flush out any carbon fines and air. Check every connection with a dry hand or tissue — any dampness means re-tighten or re-seat that joint.

Tips for a leak-free fit

• Do not over-tighten plastic fittings — hand-tight plus a quarter turn is usually enough.
• Cut tubing square (not at an angle) for a proper push-fit seal.
• Replace the cartridge on schedule — a clogged cartridge forces water past seals and causes leaks. See our guide on when to change your cartridge.