Fix a Leaky Faucet: Replace a Worn Compression Valve

Faucet leaks aren't mysterious. They're predictable failures of simple mechanical parts wearing down over years of daily use. The compression valve—that screw-down mechanism inside most traditional faucet handles—uses a rubber washer pressed against a brass or ceramic seat to stop water flow. When the washer hardens or the seat corrodes, water seeps through, one drop at a time. The math is brutal: a single drip per second adds up to 3,000 gallons a year. The good news is that fixing it requires no special skills, no soldering, and parts that cost between five and fifteen dollars. This is exactly the kind of repair that builds confidence—you disassemble, identify the worn piece, swap it for a new one, and walk away dry-handed. The decision point is simple: do you replace just the washer and seat, or swap the entire valve cartridge? If the faucet is old, the seat might be corroded beyond a simple washer change. If it's relatively new, a fresh washer often solves the problem permanently. Either way, you're looking at a straightforward afternoon job that saves money and stops that infernal dripping.

1. Kill the Flow First. Locate the shut-off valves under the sink—there should be one for hot and one for cold water, with small oval handles. Turn both clockwise until they stop. If the valves are stuck or missing, shut off water at the main house valve. Once the valves are closed, turn on the faucet and let any residual water drain out. This prevents water from spraying when you open the faucet body.
2. Pop the Handle Off. Look for a small screw or set screw on the handle itself—it's often hidden under a decorative cap or collar. For knob handles, the screw is usually on the side or hidden under a colored plastic cap you pry off. For lever handles, check the back where the lever meets the base. Loosen this screw with a screwdriver or hex wrench, then pull the handle straight up and off the faucet body. Set the screw in a small container where it won't roll away.
3. Loosen the Big Nut. Under the handle, you'll see a large hexagonal nut—the packing nut—that holds the valve stem to the faucet body. Using an adjustable wrench, turn it counterclockwise. It will require firm pressure; don't be gentle. Once it's loose enough, unscrew it by hand the rest of the way. Place it on your work surface where you can find it again.
4. Pull the Stem Out. Grip the valve stem (the threaded shaft that was under the handle) and pull it straight up and out of the faucet body. It will slide out smoothly if water is fully shut off. Lay it on your work surface. This is the mechanism that opens and closes the water flow—and inside the bottom of it is the rubber washer that's likely worn out.
5. Check for Corrosion. Look inside the faucet body where the stem just came out. You'll see a small recessed opening at the bottom—that's the valve seat, the brass or ceramic surface the washer presses against. Shine a light in and examine it. If it's smooth and shiny, you can reuse it. If it's rough, pitted, or corroded (looks dull or has white deposits), it needs replacing. Use your finger to feel the surface—it should be smooth like polished brass, not grainy or pitted.
6. Unscrew the Bad Washer. At the very bottom of the valve stem is a brass or stainless screw holding a rubber or silicone washer in place. Use a screwdriver (usually a flat-head, sometimes Phillips) to unscrew it counterclockwise. The washer will be underneath—it's usually dark, possibly brittle, and shaped like a small disc. Remove it and discard it. This is almost always the culprit.
7. Install Fresh Rubber. Get a replacement washer kit (usually a small assortment of sizes for under $5). Compression faucet washers are standard sizes—most common are ½ inch and ¾ inch. If you're unsure which size, bring the stem with you to the hardware store and hold it up to the kit. Slide the new washer onto the stem (flat side first, cup side up), then screw the brass screw back in firmly—snug, not gorilla-tight. The washer should be held securely without excessive pressure that might damage it.
8. Polish the Brass. If you decided the seat doesn't need replacing, clean it anyway. Use a damp cloth or a brass-bristled brush to wipe away any mineral deposits, debris, or corrosion from the seat surface. Shine it as much as you can—you want the new washer to make full contact with a smooth surface. If there are stubborn deposits, use a non-abrasive cleaner like vinegar on a cloth, then dry thoroughly.
9. Swap the Seat. If the seat was pitted or corroded, remove it with a seat removal tool. The tool has a T-shaped handle with a socket that grips the seat from above. Insert it into the faucet body, turn counterclockwise until it catches the seat, then pull upward. The old seat will lift out. Discard it. Get a new seat of the same size and material (usually brass) from your hardware store. Insert it straight down into the opening and screw it clockwise by hand until snug—don't overtighten.
10. Seat the Stem. Hold the valve stem vertically and insert it back into the faucet body, aligning the notches or threads so it slides straight down. Push it in until it bottoms out—you shouldn't force it, but there should be firm contact. The stem should feel secure and centered.
11. Snug the Nut. Screw the packing nut back down by hand as far as it will go, then use your adjustable wrench to tighten it clockwise. This nut compresses the packing material around the stem to prevent leaks from the handle area. Tighten firmly but don't over-crank it—you want it snug enough that no water weeps around the handle when the faucet is on.
12. Turn It Back On. Slide the handle back onto the stem, aligning the screw hole. Insert the screw and tighten it firmly—not so tight that it cracks the handle, but snug enough that the handle doesn't wobble. Screw any decorative cap back on if there is one. Now turn both shut-off valves under the sink counterclockwise to restore water pressure.
13. Watch for Drips. Turn the faucet handle fully on and fully off several times to cycle the new washer. Let the water run for 30 seconds at both hot and cold. Now turn it off and watch the spout for a full minute. A properly seated washer should show zero drips—not even a hesitant leak every few seconds. If it drips steadily, the seal didn't hold. Check that the packing nut is tight and the washer is properly seated. If it still leaks, the seat may be too damaged and needs replacing.