How to Install an Under-Sink Water Filter
Premium drinking water for $200 + 60 minutes.
TL;DR
Under-sink filters (carbon, RO, or combination) deliver premium drinking water at the kitchen sink. Most are DIY-installable in 60 minutes. RO systems use 4-5 stages for best taste/purity. Annual filter replacement.
What’s in this guide
- Choose system type
- Tools
- Tee into supply
- Install dispenser faucet
- Connect drain (RO)
Under-sink water filtration delivers premium drinking water at one fixture (usually kitchen). Various systems range from $80 carbon filter to $400 7-stage RO with mineral re-add.
Tools & Materials You’ll Need
Tools
- Drill (for dispenser hole)
- Hole saw or knockout (sink)
- Adjustable wrench
- Channel-lock pliers
Materials
- Filter system
- Dispenser faucet
- Tee adapter for supply
- Drain saddle (RO only)
Step-by-Step Instructions
Choose Filter Type
Carbon: removes chlorine, taste, basic contaminants. $80-$150. RO: removes everything to drinking-water purity. $200-$500. Combo systems available.
Drill Hole for Dispenser
Most kitchen sinks have a knockout for an additional faucet — push it out. If no knockout, drill 1-1/4″ hole in stainless sink with proper bit. Granite or composite counters: pro work.
Install Dispenser Faucet
Drop dispenser shaft through hole. Tighten mounting nut from below.
Tee Into Cold Supply
Shut off cold water valve at sink. Disconnect cold supply line. Install tee adapter — one branch to filter, one back to sink supply.
Mount Filter Housing and Connect Tubes
Mount filter to inside of cabinet wall. Connect tubing per manufacturer instructions. Color-coding helps avoid mistakes.
Connect Drain (RO Only)
RO systems produce wastewater. Install drain saddle on sink drain pipe (above the trap). Connect drain tube from filter to saddle.
Test and Flush
Restore water. Run dispenser to flush filters per manufacturer instructions (5-10 minutes for new carbon, 30+ for RO). Discard initial water.
For LA homes, an RO system pays back in bottled water savings within 12-18 months. A family of 4 buying bottled water spends $40-$60/month. RO costs $20/year in filter replacements. Plus the convenience of unlimited drinking water at the tap.
RO removes minerals
RO water is essentially mineral-free. Some find this taste flat. Add a “remineralization” stage for richer taste.
Real Scenarios from Our LA Service Calls
RO install with mineral re-add
Family wanted premium drinking water. Installed 7-stage RO with alkaline mineral cartridge. Delivers TDS under 30 ppm with mineral re-add. Cost: $385. Eliminated bottled water purchases.
When to Call a Plumber Instead
DIY isn’t always the right call. Bring in a licensed plumber if any of these apply:
- Hole drilling in granite/quartz countertop
- Custom multi-zone water filtration
- Whole-house systems
Frequently Asked Questions
Carbon vs RO?
Carbon: cheaper, basic filtration, retains minerals. RO: premium purity, more expensive, removes everything (good and bad).
Filter replacement frequency?
Carbon: every 6 months. RO membrane: every 2-3 years. Sediment pre-filter: every 6 months.
Will RO save money on bottled water?
Yes — typically pays back in 12-18 months for family of 4.
Is RO water safe to drink?
Yes, completely. Some add minerals back for taste/health benefit.
How long do these systems last?
15+ years for housing. Filter replacements as scheduled.
Need professional help in Los Angeles?
Same-day service. Flat-fee pricing. No surprise add-ons.
Call (818) 938-8660
