How to Fix a Leaky Bathroom Sink in 6 Steps

A dripping bathroom sink wastes about 200 gallons of water a month and costs roughly $25 a year — but it’ll also signal to every plumber in your neighborhood that you might be good for a $150-$300 callout. Most leaks come from worn washers or failed cartridges, and the fix is usually $5-$25 in parts and 20-45 minutes of work.

This guide walks through diagnosing which type of faucet you have, then repairing the specific component that’s failing. I’ve fixed both compression and cartridge faucets in my own house, and the key is identifying the right type before you start taking things apart.

What you’ll need

Tools:

  • Basin wrench (14” model works for most sinks)
  • Adjustable wrench
  • Flathead screwdriver
  • Phillips screwdriver
  • Bucket or towel
  • Flashlight

Materials:

  • Washer assortment kit ($3-$8) — for compression faucets
  • Replacement cartridge ($15-$40) — for cartridge faucets, brand-specific
  • Plumber’s grease or silicone-based faucet grease ($4-$6)
  • Valve seat replacement kit ($8-$15) — only if needed after diagnosis

A note on recommendations: This article contains affiliate links to tools and materials we’ve tested. We only recommend products we’d use ourselves.

Prerequisites:

  • Access to shutoff valves under the sink
  • Ability to identify your faucet type (covered below)

Before you start

Shut off the water at the shutoff valves under the sink. Turn both valves clockwise until they stop. Open the faucet to verify no water flows and to drain residual pressure from the lines.

Plug the drain opening with a rag. Small screws and washers disappear into drains instantly.

Place a bucket or towel under your work area — residual water will drip when you disconnect components.

Step 1: Identify your faucet type

Bathroom sink faucets fall into two main DIY-repairable categories:

Compression faucet: Two separate handles (hot and cold), usually in older homes. These use rubber washers that wear out. Easiest to fix.

Cartridge faucet: Single handle or two handles on one shared body. These use a cartridge mechanism that controls flow. Moderate difficulty; requires exact-match replacement cartridge.

Look at your faucet. If you have two separate handles that turn multiple rotations to fully open, you have a compression faucet. If you have a single lever or two handles that move only a quarter-turn, you have a cartridge faucet.

Step 2: Remove the handle and access the mechanism

Collection of plumbing tools including wrench, screwdriver, and bucket on a flat surface, ready for sink repair.
Photo by Şahin Sezer Dinçer on Pexels

For compression faucets:

Pop off the decorative cap on top of the dripping handle (use a flathead screwdriver gently). You’ll see a screw underneath. Remove it with a Phillips screwdriver and lift the handle straight up.

Use your adjustable wrench to loosen the packing nut — the large hexagonal nut at the base of the exposed stem. Turn counterclockwise. It may be tight; apply steady pressure without forcing it.

Pull the stem straight up and out of the faucet body.

For cartridge faucets:

Remove the handle screw (often hidden under a cap or set screw on the side). Lift off the handle.

You’ll see either a retaining nut or a cartridge collar. Loosen it with an adjustable wrench or the cartridge removal tool specific to your brand (Moen, Delta, and Kohler each use different mechanisms).

Step 3: Diagnose the failing component

Compression faucet diagnosis:

Look at the bottom of the stem you just removed. You’ll see a small brass screw holding a rubber washer. If the washer is cracked, hardened, or disintegrated, that’s your leak source.

Also inspect the valve seat — the metal ring inside the faucet body where the stem was seated. Shine a flashlight into the opening and feel the surface with your finger. If it’s rough, pitted, or corroded, the valve seat needs replacement even if you swap the washer.

Cartridge faucet diagnosis:

Cartridge faucets don’t have washers. The cartridge itself controls flow, and when it fails, you replace the entire unit. The key is getting the exact model for your faucet brand. Check the faucet body for a brand name or model number, or bring a photo of the faucet and the old cartridge to the parts counter.

Step 4: Replace the worn component

For compression faucets with bad washers:

Unscrew the small brass screw at the bottom of the stem, remove the old washer, and note its size (usually 5/8” or 3/4” for bathroom sinks). Install a new washer from your assortment kit — it should fit snugly in the seat at the bottom of the stem and tighten the screw.

Apply a thin coat of plumber’s grease to the stem threads before reinstalling. This prevents future seizing and makes the next repair easier.

For compression faucets with corroded valve seats:

Use a valve seat removal tool (part of most replacement kits or available separately for $8-$12). Insert it into the valve seat inside the faucet body and turn counterclockwise to unscrew the old seat.

Screw in the new valve seat by hand, then firm it up with the removal tool. Don’t overtighten — snug is enough.

For cartridge faucets:

Lightly grease the new cartridge with plumber’s grease. Align the cartridge so the hot/cold indicator matches your faucet orientation (usually a flat side or tab on the cartridge body lines up with a groove in the faucet). Insert the cartridge and secure the retaining nut or collar.

Step 5: Reassemble and test

Person's hands working on bathroom sink faucet repair under the sink counter with tools visible.
Photo by Kindel Media on Pexels

Reinstall the stem (for compression faucets) or cartridge collar (for cartridge faucets). Tighten the packing nut or retaining nut — snug, not crushing. Overtightening can crack plastic components or seize the mechanism.

Reattach the handle and screw. Replace the decorative cap.

Turn the shutoff valves back on slowly. Opening them too fast causes water hammer (a loud bang in the pipes). Open each valve a quarter-turn at a time and listen for flow.

Verify it worked

Open the faucet and let it run for 30 seconds. Close it completely and watch for drips from the spout.

Check under the sink for leaks at the supply line connections and the base of the faucet. If you see water pooling, the packing nut may need another quarter-turn of tightening.

Let the faucet sit closed for 5 minutes, then check again. Some drips take a minute to appear after reassembly.

Troubleshooting

Problem: Faucet still drips after replacing the washer

The valve seat is likely corroded or pitted. Go back to Step 4 and replace the valve seat. A new washer won’t seal against a damaged seat.

Problem: Water leaks from the handle base when the faucet is on

The packing nut is loose or the packing (the seal around the stem) has failed. Tighten the packing nut another quarter-turn. If that doesn’t work, you’ll need to replace the packing — a $3-$5 part available at hardware stores.

Problem: Cartridge won’t come out

Cartridges can corrode in place, especially in hard-water areas. Use a cartridge puller tool specific to your faucet brand (Moen and Delta both make them; they’re $8-$15 and worth it if the cartridge is stuck). Do not force it with pliers — you’ll crack the faucet body.

Problem: New cartridge installed but handle operation feels stiff

You may have installed the cartridge rotated 180 degrees. Remove it, rotate it a half-turn, and reinstall. Also check that you greased the cartridge before installing.

When to call a professional

Call a plumber if:

  • The shutoff valves under the sink won’t close completely or are stuck. A frozen shutoff valve indicates corroded plumbing and needs replacement before you can safely work on the faucet. I had this happen on my 1970s house — the shutoff valve stem had fused, and forcing it would have cracked the pipe.

  • Water is leaking from the supply lines or drain connections before you touch anything. This points to a structural plumbing issue beyond a simple faucet repair.

  • You’ve replaced the washer and valve seat (or cartridge) and the faucet still drips. The faucet body itself may be cracked or the threading stripped. At that point, you’re looking at faucet replacement, which is doable DIY but has higher cosmetic-install risk if you’re not confident.

  • You feel uncomfortable shutting off water or working under a sink. No shame in this. A plumber will complete the job in 30 minutes and guarantee the work.

FAQ

How long does a bathroom sink washer or cartridge last?

Washers in compression faucets last 3-7 years depending on water hardness and usage. Cartridges last 8-12 years on average. Hard-water areas see shorter lifespans.

Can I fix the leak without replacing parts?

Sometimes. If the drip is minor and the packing nut is slightly loose, tightening it a quarter-turn may stop the leak. But if the washer or cartridge has failed, tightening won’t help — you need new parts.

What’s the difference between a leaky spout and a leak under the sink?

A drip from the spout is a washer, cartridge, or valve seat problem (covered in this guide). A leak under the sink is usually a loose supply line connection or worn drain gasket. Tighten the compression nuts on the supply lines first; if that doesn’t work, you may need professional diagnosis.

Do I need to replace both faucet cartridges if only one side leaks?

No. Replace only the failing side. However, if one cartridge has failed and the faucet is over 10 years old, the other side may fail soon. Some people replace both to avoid a second repair trip.

Most bathroom sink drips are a straightforward washer or cartridge swap. The diagnosis step — identifying your faucet type and inspecting the components before buying parts — saves a trip back to the hardware store. If you’re tackling other bathroom repairs, uses a similar shut-off-and-replace approach, and is the natural next step if this repair doesn’t solve it.