A dripping faucet usually means something inside the valve has worn out, and tightening the handle won’t fix it. The drip comes from a failed seal, not from the handle being loose. Once you know which type of faucet you have, the likely cause narrows down quickly.
The Three Parts That Fail Most Often
Washers (compression faucets)
Older two-handle faucets, especially in homes built before the 1990s, are usually compression-style. Every time you turn the water off, a rubber washer presses against a metal seat to stop the flow. Do that ten times a day for twenty years and the washer wears flat, hardens, or cracks. When it can’t form a tight seal anymore, water gets past it. That’s the drip. The worn washer is the single most common cause in older fixtures.
O-rings (ball faucets and some cartridge faucets)
Ball faucets, common on single-handle kitchen faucets, have a rotating ball that controls both volume and temperature. The ball sits in a socket sealed by small O-rings and rubber seats. As those O-rings age and lose elasticity, they stop sealing around the base or the stem. You’ll often see the drip coming from around the spout base or from the handle collar rather than from the spout tip, which helps distinguish it from a washer problem.
Cartridges
Single-handle faucets from brands like Moen use a cartridge, a self-contained valve unit that slides in and out. The cartridge has internal seals and channels that control water flow. When those seals wear out, or when the cartridge body itself cracks or warps, you get a drip, sometimes at the spout, sometimes at the base. Moen cartridges are model-specific, so using the wrong replacement is a common reason a repair fails.
Ceramic disc faucets are a fourth type, less common but worth knowing. They use two ceramic discs that rotate against each other. They’re durable, but mineral deposits from hard water can score the disc surfaces or prevent them from seating flush, eventually causing a drip.
How a Plumber Diagnoses It
A licensed plumber isn’t just swapping parts at random. The diagnostic process usually goes like this:
First, they’ll identify the faucet type. The handle configuration, age of the fixture, and brand markings tell them which valve mechanism is inside before they open anything.
Then they’ll locate where the water is actually escaping. A drip from the spout tip is different from water seeping around the base or weeping from under the handle. Each location points to a different seal or part.
After shutting off the supply valves under the sink, they’ll disassemble the valve and assess the condition of the cartridge, the O-rings around it, and the valve seat underneath.
They’ll also check the valve seat itself. Even a new washer won’t seal properly against a pitted or corroded seat, so an experienced plumber will inspect and sometimes resurface the seat before reassembling.
Why This Repair Is Trickier Than It Looks
The shutoff valve under the sink has to work first. If it’s old and stuck, forcing it can cause it to fail, and now you’ve got a bigger problem than a drip. If those valves haven’t been turned in years, the whole job needs a pro.
Cartridges are model-specific. Moen alone has dozens of cartridge variations across its product line. Using the wrong one means reassembling everything and still having a drip, or worse, a new leak at the base.
The valve seat is where things often get complicated. A worn or pitted seat won’t seal no matter how new the washer or cartridge is. Inspecting and resurfacing the seat requires specialized tools and some experience to do without damaging the faucet body.
And if opening up the faucet reveals corrosion, heavy mineral buildup, or a cracked valve body, the scope changes. What looked like a simple washer swap can become a full faucet replacement, particularly on fixtures more than 20 to 25 years old.
When to Call a Licensed Plumber
Get someone in for any of these:
- The shutoff valves under the sink are stuck or haven’t been turned in years
- You replaced the cartridge or washer and the drip came back
- There’s corrosion, mineral scale, or visible damage to the valve body
- The drip is accompanied by reduced pressure or a change in how the handle moves
A faucet dripping once per second loses more than 3,000 gallons a year, per EPA WaterSense estimates. It’s worth getting fixed right the first time rather than chasing the problem through multiple attempts.
When you hire someone, verify their license at cslb.ca.gov before work starts. California requires plumbing contractors to hold a C-36 license, and a licensed plumber carries liability insurance if something goes wrong behind the wall.
Tell the plumber what you observed: which handle drips (hot or cold side), where the water appears (spout tip, base, or handle area), the faucet brand if you know it, and roughly how old the fixture is. That helps them come prepared with the right parts.