You turn the handle off, walk away, and a few seconds later you hear it again. Drip. The faucet isn't broken in any dramatic way. Somewhere inside, a part that's supposed to press tightly against a seal has stopped doing it.
What actually stops the water
Every faucet has one part that does the sealing. On most faucets made in the last thirty years or so, that's a cartridge: a cylinder inside the body that moves when you turn the handle. On older two-handle faucets, it's a rubber washer pressed against a metal seat.
Both wear out. Rubber hardens, plastic gets scratched, and minerals in the water leave deposits on the sealing surfaces. Once the seal isn't perfect, pressure in the line pushes a little water past it, and you get a drip.
The usual causes
Worn cartridge
The most common cause on single-handle faucets. The drip often gets faster over a few weeks. Replacing the cartridge with the right part for your faucet's brand normally fixes it completely.
Worn washer or damaged seat
On two-handle faucets, feel the drip. If it's warm, the hot side is worn. If it's cold, the cold side. Sometimes the washer is fine but the seat it presses against is pitted, which is why a new washer alone doesn't always stop the drip.
Debris in the valve
After water main work or a plumbing repair, a piece of grit can lodge in the cartridge and hold it slightly open. The faucet may have started dripping right after some other work was done.
Water pressure that's too high
If several faucets and toilets in the house have started dripping or running around the same time, the pressure coming into the house may be part of the problem. That's worth mentioning when you call.
What you can check yourself
- Which side is dripping, hot or cold. Feel the water.
- Whether the drip is from the spout, or from around the handle or base. Those are different problems. See leaking faucet repair for leaks that aren't at the spout.
- The faucet's brand. There's usually a logo on the handle, the base or the spout. Cartridges are brand-specific, so this saves a trip for parts.
- Whether the shutoff valves under the sink turn freely. If they don't, say so when you call.
Is it worth fixing right away?
A drip wastes more than most people expect. The EPA says a faucet dripping once per second can waste more than 3,000 gallons a year (EPA WaterSense). It also tends to get worse, and a constantly wet sink can stain the finish over time.
The repair itself is usually small. A cartridge or washer is an inexpensive part, and the job is mostly about getting the old one out without damaging the faucet body.
When a new faucet makes more sense
If the faucet is corroded, if parts for the brand are no longer made, or if it has already been repaired more than once, replacing it is often the better spend. Faucet replacement covers how to decide.