Fix a Leaky Bathroom Sink Faucet

A dripping faucet is one of those problems that seems small until you realize it's wasting thousands of gallons a year and running up your water bill. The good news: the fix is straightforward, and you probably already have most of the tools you need. The leak almost always traces back to the same culprit—a worn washer, O-ring, or cartridge inside the faucet body. The specific repair depends on what kind of faucet you have (compression, ball, cartridge, or ceramic disk), but the principle is the same: identify the leak source, turn off the water, and swap the worn part. You'll spend less than thirty dollars and an afternoon, and your faucet will run tight again.

1. Know Your Faucet Type. Look at your faucet and count the handles. A single handle that moves side-to-side is likely a ball faucet. A single handle that moves up and down is a cartridge faucet. Two separate handles—one hot, one cold—means you have a compression faucet. A single handle with a lever on top is a ceramic disk faucet. This matters because each type leaks differently and requires a different repair. Write down your faucet type before moving forward.
2. Kill the Water First. Look under the sink at the supply valves—you'll see two knobs (hot and cold) connected to copper or flexible lines running up to the faucet. Turn both clockwise until they stop. They don't need much force; hand-tight is enough. If your supply valves are stuck or missing, you may need to shut off the main water valve to the house (usually in the basement or near the meter). Open the faucet to confirm the water is off—it should run dry within seconds.
3. Organize Your Space. Place a wet rag or stopper in the sink drain so small parts don't disappear. Clear the area under the sink and spread out a towel or drop cloth. Have your adjustable wrench, screwdrivers, and new parts within arm's reach. Keep a small container or zip-lock bag nearby to hold the parts you remove—don't mix them up.
4. Expose the Stem. For a two-handle compression faucet, look for a small screw or set screw on the handle. It's often hidden under a decorative cap or button. Pry the cap off gently with a flathead screwdriver and remove the screw. The handle will now slide or twist off. Set it aside safely. If your faucet is ball, cartridge, or ceramic disk, skip this step and proceed to the next.
5. Extract the Core. For a compression faucet: Use your adjustable wrench to turn the large hexagonal nut at the base of the stem counterclockwise. Turn slowly and steadily; it should loosen without stripping. Lift the entire stem assembly straight out. For a cartridge faucet: Look for a small metal clip or set screw near the base of the handle. Remove it with a wrench or hex key. The cartridge will now slide straight up and out of the faucet body. For ball and ceramic disk faucets, see the specific steps below.
6. Swap the Washer. Once the stem is out, you'll see a flat washer at the base held by a screw. Unscrew it and remove the washer. This is usually your leak culprit. Take the old washer to your hardware store and buy an exact replacement (usually a pack of assorted brass washers costs a few dollars). Screw the new washer back on tightly. While you're at it, check the O-ring just above the washer. If it looks cracked, dry, or damaged, unscrew it and replace it too—O-ring kits are cheap and easy swaps.
7. Install Fresh Cartridge. Once the cartridge is out, bring it to your hardware store or note the model number (stamped on the side). Buy an exact replacement—cartridges are faucet-specific and cost between fifteen and forty dollars depending on the brand. Insert the new cartridge into the faucet body the same way the old one came out. Make sure it's seated all the way in. Reinstall the retaining clip and tighten it so the cartridge doesn't shift.
8. Resurface the Valve Seat. If you've replaced the washer and the faucet still leaks from the spout, the problem is likely a corroded valve seat. Look at the inside of the faucet body where the stem was. You'll see a flat, circular metal seat. If it looks pitted, corroded, or rough, you have two options: scrape it lightly with a valve seat dresser tool (a small device that costs five to ten dollars) to smooth it, or replace it entirely. For a full replacement, unscrew the old seat with a valve seat wrench and screw in a new one. A new valve seat costs under five dollars.
9. Replace Ball & Seals. Ball faucets leak from the spout when the ball itself wears, or from the handle base when seals deteriorate. For most people, replacing the entire ball and seal kit is simpler than individual parts. Loosen the set screw under the handle with a hex key, remove the handle, then use the spanner wrench (included in most ball faucet kits) to unscrew the collar nut. The ball will lift out. Buy a replacement ball and seal kit for your faucet model. Install the new kit by reversing these steps. Most kits come with new springs and seals that address the usual leak points.
10. Refresh Disk Seals. Ceramic disk faucets rarely leak from the spout itself because the disk is durable. Most leaks come from the base where the handle connects. Remove the handle set screw, then loosen the large cap at the base with a wrench. Lift off the cap and you'll see inlet and outlet seals. These rubber seals dry out and crack over time. Remove and replace them—they're inexpensive and come in kits. Reinstall the cap and handle. If the faucet still leaks, the ceramic disk itself may be cracked, and the whole cartridge will need replacing.
11. Put It Back Together. Reverse your disassembly steps to put the faucet back together. For compression faucets, screw the stem back in hand-tight, then use your wrench to turn the packing nut until snug. Don't over-tighten. For cartridge faucets, slide the cartridge in, reinstall the clip, and reattach the handle. For ball and ceramic disk, follow the manufacturer's instructions (they came with your kit). Once assembled, turn the supply valves back on slowly. Open the faucet hot and cold and let water run for ten seconds to purge air from the lines. Check for leaks at the spout and around the base.
12. Test & Verify. Dry the area under the sink, dispose of old parts and packaging, and return your tools. Use the faucet normally over the next day. Drips should stop immediately. Some faucets take a few hours to settle, but a continuous leak means something wasn't seated correctly. If you see a new leak, turn the water off again and check your reassembly against your reference photo.