Fix a Leaking Bathroom Sink Faucet

A dripping faucet is one of those small problems that becomes loud and expensive the moment you stop ignoring it. That steady drip wastes water, runs up the bill, and wears out your sink finish. The good news: the fix is almost always inside the faucet body itself, and you don't need a plumber. Most leaks come from washers or seals that have simply worn out from years of turning the handle on and off. The work is straightforward—you're mostly just taking the faucet apart, identifying which part has failed, and swapping it for a new one. The whole job takes an afternoon, costs under forty dollars, and teaches you exactly how your faucet actually works. The type of faucet matters here. Single-handle faucets use a cartridge or ball mechanism. Two-handle faucets use washers and valve seats. Once you identify which you have, the repair becomes obvious. This guide covers both, and walks you through diagnosing the leak, gathering the right parts, and reassembling everything so it works like new.

1. Stop the Flow First. Locate the shutoff valves under the sink—there should be two, one for hot and one for cold. Turn both handles clockwise until they stop. Open the faucet at the sink to confirm the water is off. If the valves are stuck or missing, shut off the main water supply to the house before continuing.
2. Know Your Enemy. Look at the 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. Single-handle leaks usually point to a cartridge failure. Two-handle leaks usually point to a worn washer. This determines which parts you'll need to buy.
3. Expose the Hidden Screw. On single-handle faucets, look for a small colored disc (usually red for hot, blue for cold) on the side or top of the handle. Pry it out gently with a flathead screwdriver or small knife. On two-handle faucets, look for a small cap covering the handle screw—pry this off the same way. Set these pieces in a safe place; they're small and easy to lose.
4. Release the Handle. You'll now see a screw under the cap you just removed. Use the appropriate screwdriver (usually Phillips) to unscrew it. The handle will slide off. On cartridge faucets, there may be a collar or retaining nut behind the handle—loosen it with a wrench or your fingers and set it aside.
5. Clear the Work Space. The escutcheon is the flat ring around the base of the faucet. On some models, it unscrews with a wrench or comes off after you remove the handles. On others, it's glued on and you can skip this step. Removing it gives you better access to the cartridge or valve seat underneath.
6. Pull the Bad Cartridge. Once the handle is off, you'll see the cartridge—a cylindrical piece about two inches long in the center of the faucet body. Use a cartridge puller tool (a cheap brass tool that costs five dollars) or needle-nose pliers to grip and pull it straight out. The cartridge is what actually controls water flow. When it wears out, water leaks past the internal seals.
7. Swap the Worn Parts. For two-handle faucets, use a wrench to unscrew the valve seat (the brass piece in the center of the faucet body where the stem screws in). Remove the old rubber washer and brass valve seat screw. Buy a replacement kit for your faucet model—it includes new washers and a valve seat. Install the new pieces in reverse order: brass screw first, then rubber washer, then screw in the new valve seat.
8. Get the Right Part. Take your faucet model number (usually stamped on the underside of the spout or on the back of the escutcheon) to the hardware store. For single-handle faucets, buy a cartridge kit for your specific model—Moen, Delta, and Kohler cartridges are not interchangeable. For two-handle faucets, buy a washer and seat replacement kit. The parts cost between five and twenty-five dollars.
9. Seat the New Part. For single-handle faucets, insert the new cartridge straight down into the faucet body, aligning it with the marks you made earlier. It should slide in smoothly without forcing. For two-handle faucets, install the new valve seat by hand first, then tighten with your wrench until snug (not hard). Both types should feel secure but not over-tightened.
10. Put It Back Together. Reverse the disassembly steps: slide the handle back on, screw it down with the Phillips screw, then snap the index button or cap back over the screw hole. Hand-tighten everything—you don't need a tool for the handle screw.
11. Confirm It Works. Open both shutoff valves under the sink slowly, starting with one. Listen for water to fill the lines. Turn on the faucet and let it run for 30 seconds to clear any air. Check both the hot and cold handles, and inspect under the sink for any leaks around the valve connections. The faucet should run smoothly with no drips when the handle is fully off.