How to Fit an Inline Water Filter — UK Kitchen Guide
An undersink inline filter delivers filtered cold water via a dedicated tap. Better than jug filters, no fridge space, and £80 install.
Step-by-step method
1. Choose filter type
Carbon block for taste/chlorine. Reverse osmosis for hardness/nitrates. 3M AP-DWS1000 and BWT AQA are UK trade favourites.
2. Fit tee off cold supply
Under sink, tee off the cold with a 15mm × 15mm × 15mm or self-piercing valve.
3. Mount filter housing
Vertical, cartridge down, on cupboard wall. Isolator between tee and filter for cartridge change.
4. Fit dedicated tap
1/4" or 3/8" push-fit tubing to tap on sink or worktop. Small hole (18mm) drilled if none exists.
5. Flush and taste
Run 10L through new cartridge to flush carbon dust. Note install date — cartridge lasts 6–12 months.
Frequently asked questions
Do I need a water softener too?+
Softener treats whole-house hardness. Inline filter is drinking-water only. Different jobs, sometimes both worthwhile in hard-water areas.
How much does an under-sink water filter cost to run?+
Cartridge £30–£60/year. Water cost negligible. Cheaper than bottled water within 2 months.