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How to Install an Under Sink Water Filter (Step-by-Step with Tools)

Why Install an Under Sink Water Filter?

If your tap water has a weird taste, smells off, or leaves residue on your sink, an under sink water filter is one of the best home upgrades you can make — and you can install it yourself.

Modern systems like Waterdrop’s G3P800 or G5P500 are tankless, efficient, and surprisingly easy to mount with the right tools.

Here’s how to do it step by step — no plumber required.

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Tools & Materials You’ll Need

Before you get started, make sure you have the right setup:

Tools:

Materials:

  • Your water filter system (e.g., Waterdrop G3P800, G5P500, or 10UA)
  • Mounting screws and tubing (usually included in the box)
  • Bucket or towel for small water spills
  • Safety gloves (optional)

👉 See all our top-rated tools on the Tools We Recommend page.

Step-by-Step: How to Install an Under Sink Water Filter

1. Clear Out Your Cabinet

Remove everything from under your sink.
Lay down a towel or mat in case of minor spills.
Locate the cold water shutoff valve and test it.

Pro Tip: If your valve is stuck, use a little WD-40 or gently turn it with pliers. Don’t force it.

2. Shut Off the Cold Water

Turn off the cold water valve under the sink.
Then turn on the faucet to relieve pressure.
You’ll likely have a bit of water left in the line — keep a towel or bucket handy.

3. Mount the Filter System

Use the included template or mounting holes to install the filter unit (or bracket) on the back or side wall of your cabinet.
Drill pilot holes and screw the unit securely in place.

Tip: Leave enough room underneath the unit to change filters later.

4. Install the Filter Faucet (If Included)

If your system includes a dedicated filtered water faucet:

  • Pick a spot on your sink or countertop (often near the soap dispenser)
  • Drill a hole if needed (usually 1⅜” bit)
  • Insert the faucet, tighten from underneath, and connect tubing
  • Some faucets include TDS monitors — attach the wiring if provided

Note: Stainless sinks are easier to drill. Granite or quartz may require special bits or professional help.

5. Connect the Inlet Hose

Disconnect the cold water line from your shutoff valve.
Attach the provided T-connector (included with most systems).
Wrap threads with Teflon tape before tightening.

  • One side goes back to your faucet
  • One line goes to your filter system inlet
  • Hand-tighten, then snug with a wrench — don’t overtighten

6. Connect the Outlet Hose

Run the output tubing from the filter system to:

  • Your dedicated filtered faucet (if installed), or
  • The included adapter line for shared faucet setups

Secure all push-fit or compression connections. You should hear or feel a “click.”

7. Connect the Drain Line (RO Systems Only)

If you’re installing a reverse osmosis system, it will have a small drain line:

  • Drill a hole into your drainpipe or install the included drain saddle
  • Position it above the P-trap
  • Tighten with a screwdriver and insert the tubing

Important: This prevents wastewater from backing up into the system.

8. Turn On the Water and Test

Slowly turn the cold water valve back on.
Check for leaks at every connection.

  • Open your filtered faucet and let water run for 5 minutes
  • For RO systems: flush for 30–60 minutes on first use
  • Watch for drips under the sink over the next hour

9. Secure and Tidy Everything

Bundle tubing neatly with clips or zip ties.
Store any leftover parts or manuals somewhere handy — filters need to be changed every 6–12 months depending on model.

Optional Upgrades

  • Smart faucet with TDS meter
  • Remineralization filter (for RO systems)
  • Leak detection sensor
  • Under-sink light strip for better visibility

Final Thoughts: It’s Easier Than You Think

Installing an under sink water filter can seem intimidating — but once you break it down, it’s a straightforward process most homeowners can do in under an hour.

Plus, the payoff is huge: cleaner, safer water every single day — without the cost of bottled water or relying on whatever your tap provides.

👉 Want help choosing the right system? Check out our full Waterdrop system comparison here →

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