Fixing a dripping faucet starts with the valve under the sink

Quick answer: Shut the water off under the sink, then find out what kind of faucet you have before you buy anything. A drip from the spout means a worn washer or cartridge. A leak around the handle means an O-ring.

Most faucet repairs go wrong in the hardware store, not at the sink. You walk in on a Saturday with a vague description ("silver, one handle, kind of curved") and stand in front of a wall of forty cartridges that all look the same. Then you walk out with the wrong one. The fix is simple. Take the faucet apart first, then shop with the old part in your hand.

But before any of that, there's the valve.

Start with the shut-off, and treat it gently

Open the cabinet under the sink. You should see two small valves on the pipes coming out of the wall, one for hot and one for cold. Each one feeds a flexible line up to the faucet. Turn each valve clockwise until it stops.

This is where most people get their first surprise. A valve that hasn't moved in fifteen years doesn't want to move now. The older multi-turn kind, with a round or oval handle, is the usual offender. Use your hand only. If it won't turn, don't clamp pliers on it and lean. A brass stem that's been sitting in hard water can snap, or the packing behind the handle can start leaking. Then your drip becomes a spray inside a cabinet full of dish soap and paper towels.

If a valve weeps a little around the stem after you turn it, tighten the small nut just behind the handle about an eighth of a turn. That usually stops it.

If a valve won't close at all, go to the main. It's usually where the water line enters the house, often in the basement, garage, crawlspace or near the water heater. Find it this week, before you need it. Make sure everybody in the house who's old enough knows where it is too. That's worth more than anything else in this piece.

Once the water's off, open the faucet to let the pressure drain. Then close the drain stopper or stuff a rag in the drain. You're about to handle a screw the size of a grain of rice, and the drain wants it.

Figure out what you're actually fixing

Where the water comes from tells you most of what you need to know.

• Drips from the spout when the faucet is off: the seal inside is worn. On an old two-handle faucet that's the washer. On most newer ones it's the cartridge.
• Water around the base of the handle while it's running: an O-ring or packing. Cheaper and easier.
• Water under the sink: not a faucet repair. Check the supply line connections and the valve itself first.

On a two-handle faucet, find out which side is leaking before you take anything apart. Shut off only the hot valve. If the drip stops, it's the hot side. That saves you doing the job twice.

Then work out the type:

• Compression: two handles that you crank down to stop the water. They feel mushier as they wear. There's a rubber washer inside. Common in older houses.
• Cartridge: one or two handles that move smoothly. A plastic or brass cylinder inside does the work. Moen single-handle faucets use them, and you'll see the Moen 1225 hanging in every hardware store in the country.
• Ball: a single handle on a domed cap, typical of older Delta kitchen faucets. You repair it with a kit of small rubber seats and springs.
• Ceramic disc: a single lever over a wide cylinder. The discs rarely fail. The rubber seals under them do.

The tools

You don't need much:

• An adjustable wrench, with the jaws wrapped in painter's tape so you don't chew up the finish
• A flathead and a Phillips screwdriver
• A small hex key set, since handle setscrews are often tiny
• Needle-nose pliers and a flashlight
• A towel and a tube of silicone faucet grease (not petroleum jelly, which is hard on rubber seals)

Your phone counts too. Photograph every step.

Lay the towel on the counter and set each part down in the order it came off, left to right. Reassembly goes right to left.

Fixing a cartridge faucet

Pry the decorative cap off the handle with a thin flathead. Remove the screw underneath and lift the handle off. If there's no cap, look for a setscrew under the lever and use the hex key.

Under the handle you'll find either a retaining nut or, on many Moens, a U-shaped clip at the top of the faucet body. Pull the clip straight up with the needle-nose pliers. Before you pull the cartridge, note which way it's facing. Take a photo. Seriously.

Then pull. Sometimes the cartridge slides right out. Sometimes years of mineral deposits have cemented it in place and it won't budge. Don't wrench on it sideways, because you can crack it and leave half of it stuck in the body. Moen and others sell an inexpensive cartridge puller built for exactly this, and it's worth the trip.

Take the old cartridge to the store and match it in your hand. The brand name on the faucet helps, but the part itself settles it.

Before the new one goes in, wipe out the faucet body and put a thin coat of silicone grease on the O-rings. Seat the cartridge facing the same way as the old one. If your hot and cold come out reversed when you're done, the cartridge is turned 180 degrees. That's an annoying but quick fix. Take the handle back off and rotate it.

Fixing a compression faucet

Remove the handle the same way. Underneath is a packing nut. Unscrew it with the wrench. Then unscrew the whole stem out of the body, turning it the same direction you'd turn the faucet on.

At the bottom of the stem is a rubber washer held on by a small brass screw. Replace both. Old screws corrode, and a new one costs almost nothing. Washers come in assortment packs. Match both the size and the shape, since some are flat and some are beveled.

Now for the part the instructions leave out. Shine your flashlight down into the faucet body at the brass seat the washer presses against. If the seat is pitted or grooved, a new washer will drip again within weeks because it's sealing against a rough surface. You can unscrew the seat with an inexpensive seat wrench and replace it, or smooth it with a seat dressing tool. If you skip this step, you'll be back under the sink soon.

If the handle was leaking, replace the O-ring or packing on the stem while it's out. Then grease it, reassemble it and snug it down. Don't crank it.

Turning the water back on

First, unscrew the aerator from the tip of the spout. Open the faucet, then open the shut-off valves slowly and let the water run for a minute. Any grit knocked loose inside the pipes flushes out the open spout instead of lodging in your brand-new cartridge.

While the aerator's off, soak it in white vinegar for an hour. Scale builds up in that little screen and kills your water pressure. Rinse it, screw it back on, and the faucet runs better than it did before you touched it.

Then wipe down the cabinet. Put a strip of tape on each valve marked HOT and COLD. Whoever reaches for them next will be glad you did, and that might be you at 11 p.m. with water on the floor.

When to stop

Some faucets aren't worth saving. If the body is corroded, if parts for that model are discontinued, or if you've replaced the cartridge twice and it still drips, a new faucet is often the better use of your Saturday. The same goes if the shut-off valve itself is failing. Replacing those is real plumbing work, and it's perfectly reasonable to hand it to a licensed plumber.

If you rent, the faucet belongs to your landlord. Report the drip in writing, with the date, and let them fix it. Taking apart fixtures you don't own can put the repair, and the bill, on you.

If you own the place, though, the drip is yours. Sooner or later the man behind the counter will ask what kind of faucet you've got. Don't describe it. Set the cartridge on the counter.