A bathroom faucet that drips once a second wastes around 3,000 gallons of water a year, per the EPA’s WaterSense program — and that’s before it starts staining porcelain. If yours has been plink-plink-plinking for a week, the fix on almost every modern single-handle faucet is the same: swap the cartridge. It runs $10 to $20 in parts, takes about 20 minutes, and doesn’t need a plumber or a whole Saturday.
Why It’s Almost Always the Cartridge
Modern single-handle bathroom faucets — most Moen, Delta, Kohler, and Pfister models made in the last 25 years — use a small brass or ceramic-disc cartridge inside the handle that controls both temperature and flow. When the internal O-rings or discs wear out (usually 8 to 15 years in, faster in hard-water areas), water sneaks past even when the handle is fully closed. On a two-handle faucet, the wear part goes by a different name — a stem-and-seat assembly or a rubber washer under the packing nut — but the diagnosis is the same. Nine times out of ten you don’t need a new faucet. You need a $10 cartridge from the same brand.
What to Gather Before You Turn the Water Off
You want everything on the counter before the supply valves close — trotting to the hardware store with a half-open faucet is nobody’s idea of a Sunday morning. The short list:
- Small adjustable wrench or channel-lock pliers
- Phillips and flathead screwdrivers
- A replacement cartridge that matches your faucet’s brand and model — a Moen 1225 or a Delta RP19804 covers a huge share of American homes
- A shop rag and a small bowl for trapped water
- A $5 tub of silicone plumber’s grease — the step most tutorials skip and the reason a lot of DIY swaps start dripping again in six months
If your kit is thin on basics, our starter home toolkit list covers what you’ll reach for on any small-plumbing job.
The 20-Minute Swap
Shut off the hot and cold supply valves under the sink, then run the faucet to release pressure and confirm the water actually stops. Pop off the decorative cap on top of the handle with a small flathead, remove the set screw, and lift the handle straight up. Under it is a retaining nut or a horseshoe-shaped clip holding the cartridge in place — unscrew it or slide it out.
Note the orientation of the old cartridge before you pull it. Hot side and cold side matter, and seating the new one 180 degrees off makes the handle feel backwards and still drip. Smear a light coat of plumber’s grease on the new cartridge’s O-rings, slide it in the same orientation, and reverse the disassembly. Turn the supply valves back on slowly and watch the base of the spout for a bead of water before you refit the handle.
What to Try If It Still Drips
Nine times out of ten, an incomplete seat is the culprit — check that the cartridge is pressed fully home. On a two-handle faucet, replace the rubber seats and springs while you’re in there; they usually come in a rebuild kit for around $6 and wear out on the same timeline. If the drip is at the base of the spout instead of the tip, a separate set of O-rings around the spout body is the fix — same session, different location.
If a fingertip along the inside of the faucet body catches on scratches, no cartridge will seal against it. That’s when full replacement makes sense — the same tools and approach apply to bathroom fixtures as kitchen ones, walked through in our kitchen faucet replacement guide.
If a small tool like a basin wrench or a decent set of channel-locks is on your “eventually” list, the running deals page is worth a 30-second look before you pay full price somewhere else.
A Two-Minute Habit That Buys You Years
Turn the handle firmly but never with force — cranking a cartridge tight to stop a drip is what wears the seal out in the first place. Once a year, wipe the base of the spout dry and watch for a slow bead of water; that tells you the underlying O-ring is next in line. Write the faucet brand and model number in pencil inside the vanity door while you have it apart, so the next part hunt is a 30-second job instead of an evening. Same trick works if you ever end up chasing a running toilet.
FAQ
How do I know which cartridge to buy?
Photograph the underside of the handle, the model markings on the spout base, and the shape of the old cartridge once it’s out. Most hardware store plumbing staff can match it on sight, and Moen and Delta both offer free lifetime cartridge replacements to the original homeowner if you can produce the part number.
Do I need to shut off the main water?
The two supply valves under the sink are enough — one for hot, one for cold. Only shut the main if a supply valve itself is stuck or leaking.
Is plumber’s grease really necessary?
It’s not required for the faucet to function, but skipping it noticeably shortens the life of the new O-rings. A $5 tub lasts through many repairs and is the cheapest way to make the swap actually last.
Photo by Erik Mclean
on Unsplash
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