Before buying a washer, find exactly where the water is escaping. A spout drip, a leak around the handle, and water at a supply connection under the sink are different repairs.
Identify the faucet mechanism
Many modern faucets use cartridges; others use ceramic disks, ball assemblies, or compression stems. Find the brand and model when possible because replacement parts must match.
Shut off water and verify it is actually off
Close the fixture stops under the sink and open the faucet to relieve pressure. If a stop valve will not shut off or begins leaking when moved, do not force it repeatedly; the main shutoff or professional help may be needed.
Protect the finish while disassembling
Cover the drain so small screws cannot disappear and use tools that will not scar chrome or plated finishes. Photograph layers or place parts in order as they come off.
Replace the wear part that matches the design
A cartridge faucet may need a cartridge or seals. A compression faucet may need a washer or attention to its valve seat. Use only plumbing-compatible lubricant where the manufacturer calls for it.
Restore water slowly and inspect two areas
Check the spout first, then every connection you disturbed under the sink. A repair that stops the drip but leaves a cabinet leak is not complete.
If parts are badly corroded, the shutoff valve does not work, or the faucet body itself is cracked, replacing the fixture or calling a plumber can be more reliable than further disassembly.
Sources
- U.S. Environmental Protection Agency WaterSense — Fix a Leak Week — Household leak detection and repair, including dripping faucets.