Fix a Leaking Bathroom Sink Faucet

A dripping faucet is one of those problems that seems small until you realize it's costing you money and wasting water every single day. That steady drip—sometimes from the spout, sometimes from under the handle—tells you a seal has failed somewhere inside the faucet body. The good news is that most bathroom sink faucet leaks are fixable without calling a plumber. You're usually looking at replacing a worn washer, an O-ring, or a cartridge, all of which cost between five and thirty dollars and take an afternoon to swap out. The leak might be hiding behind the handle, under the spout, or deep in the valve body, but once you know which type of faucet you have, the repair follows a logical sequence: turn off the water, take it apart carefully, identify the worn part, replace it, and reassemble. Done right, you'll have a dry sink and the confidence that you fixed it yourself.

1. Kill the Flow First. Look under the sink in the cabinet. You'll see two shutoff valves—one for hot water, one for cold—with oval handles pointing toward the pipes. Turn both valves clockwise until they stop. They don't need to be cranked hard; hand-tight is enough. Turn on the sink faucet to confirm the water is off. If nothing comes out, you're ready to work.
2. Know Your Enemy. Look at the faucet handle or handles. Single-handle faucets have one lever or knob that controls both hot and cold water. Two-handle faucets have separate handles for hot and cold. Cartridge faucets have a removable cartridge inside (most common in bathrooms). Compression faucets have rubber washers that compress against a valve seat. Ball faucets have a rounded cap on top. Take a photo or note the brand name if you see it on the spout or body—it helps when ordering replacement parts.
3. Remove the Handle. For single-handle faucets, look for a small set screw beneath the handle or hidden under a decorative cap. Use a hex wrench (Allen key) or small screwdriver to loosen it—don't remove it completely, just enough to slide the handle off. If there's a decorative cap covering the screw, gently pry it off with a flathead screwdriver. For two-handle faucets, look for a set screw on each handle and loosen them the same way. Pull the handle straight up and off the faucet body.
4. Loosen the Packing Nut. Under the handle, you'll see a large hexagonal nut (called the packing nut) that holds the valve assembly together. Use an adjustable wrench or basin wrench to turn it counterclockwise. A basin wrench is designed to reach into tight spaces under sinks and makes this step much easier; regular wrenches can work but require more maneuvering. Turn until the nut spins freely, then unscrew it by hand and set it aside.
5. Extract the Cartridge. With the packing nut off, you can now pull the valve assembly straight up and out of the faucet body. For cartridge faucets, you'll see a cartridge—a plastic or brass cylinder about the size of your thumb. For compression faucets, you'll see a long stem with a rubber washer at the bottom. In either case, pull straight up with steady pressure. Some cartridges have a collar or clip at the top; if so, use a cartridge puller tool (available at hardware stores for ten to fifteen dollars) or carefully pry it with a flat screwdriver while pulling up.
6. Spot the Damage. Lay the cartridge or stem on a paper towel and look closely. If it's a cartridge, you're looking for cracks, mineral buildup, or visible damage. If it's a compression stem, check the rubber washer at the bottom—it should be firm and flat, not dried out, cracked, or deformed. If you see white mineral deposits, soak the part in white vinegar for 30 minutes and scrub gently with an old toothbrush. If the washer is visibly worn or the cartridge is damaged, replacement is your only option. If you're unsure, take it to the hardware store and compare it to a new one.
7. Swap the Washer. If your faucet is a compression type and the rubber washer is worn, you need to replace it. The washer sits at the very bottom of the stem, held in place by a small brass screw. Use a small flathead screwdriver to remove that screw, pull off the old washer, and slip a new one on. The new washer must match the original in size and thickness—bring the old one to the hardware store or note its diameter. Screw it back in snugly but don't overtighten.
8. Install New Cartridge. If you have a cartridge faucet and inspection showed damage or if vinegar soaking didn't fix the leak, you need a new cartridge. Find the brand name and model number on your faucet body or packaging from when it was installed. Call the manufacturer or visit their website with the model number, or bring your old cartridge to the hardware store to match it exactly. New cartridges typically cost fifteen to forty dollars. When it arrives, insert the new cartridge into the faucet body the same way the old one came out—straight down, with the internal key or alignment marks matching the faucet body's opening. Push it down until it seats fully and click into place.
9. Put It Back Together. With the cartridge or stem in place, slide the packing nut back onto the faucet body and tighten it clockwise with your basin wrench or adjustable wrench. Tighten it snugly—firm enough that water won't leak around it, but not so tight that you crack it. You're aiming for hand-tight plus a quarter turn with the wrench. Slide the handle back onto the stem or cartridge, align the set screw hole, and tighten the set screw. If there's a decorative cap, snap it back in place.
10. Restore the Flow. Return to the shutoff valves under the sink and turn both valves counterclockwise to open them fully. Go back to the sink and turn on both the hot and cold handles. Run water for about 30 seconds to clear any air from the lines. Check the spout for steady flow and listen for any hissing or sputtering.
11. Hunt for Hidden Leaks. Turn off the faucet and watch the spout. If water continues to drip slowly, the repair didn't take—you likely have a cartridge that needs replacement or a washer that's still worn. If water is leaking from under the handle or around the packing nut, tighten that nut another quarter turn with your wrench. Let the sink sit for five minutes, then check again. Place a dry paper towel under the faucet base and leave it overnight; in the morning, any water droplets mean there's still a leak.
12. Dial In the Fit. If water is seeping around the base of the handle or spout, the packing nut is loose. Use your basin wrench to turn it clockwise another one-eighth to one-quarter turn. Test the handle movement to confirm it's still smooth. If tightening causes the handle to become stiff, you've gone too far; back off a quarter turn.