A faucet that drips once per second wastes more than 3,000 gallons a year, enough to fill a small swimming pool, and the repair usually costs under $15 in parts. A bathroom sink faucet leaking almost always comes down to a worn washer, O-ring, or cartridge, all of which you can replace yourself in under an hour. The key is identifying your faucet type first, because each design leaks for different reasons and takes different parts. This guide covers the causes, the fixes, and how to know when it is time to call a plumber.
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First, Identify Your Faucet Type
There are four common faucet designs, and knowing yours narrows the diagnosis instantly.
- Compression: The oldest style, with separate hot and cold handles you twist to a firm stop. Uses rubber washers that wear out; the classic dripping-spout faucet.
- Ball: A single handle over a rounded cap, common on older kitchen faucets but found in baths too. Many small parts inside.
- Cartridge: A single or double handle with a smooth up-and-down and side-to-side motion, controlled by a replaceable cartridge.
- Ceramic disc: A single lever over a wide cylindrical body, using two ceramic discs. Very durable but can still leak from worn seals.
If your handles twist to a hard stop, you likely have compression. If a single lever glides smoothly, it is cartridge or ceramic disc. This distinction determines everything that follows.
Common Causes of a Leaking Faucet
Leaks fall into a few categories depending on where the water appears.
Dripping from the Spout
The most common leak. On compression faucets, it is a worn rubber washer or a corroded valve seat. On cartridge or ceramic faucets, it is a worn cartridge or disc seals. Water keeps seeping past the failed part even when the handle is off.
Leaking Around the Base or Handle
Water pooling at the base of the spout or seeping from under the handle points to worn O-rings, the round rubber seals where parts join and swivel. Replacing the O-rings usually stops it.
Leaking Under the Sink
Water under the cabinet is a different problem: loose supply-line connections, a failing supply-line washer, or corrosion at the shutoff valves. Tighten fittings and inspect the flexible supply hoses.
Tools and Parts You’ll Need
- Adjustable wrench and channel-lock pliers
- Phillips and flathead screwdrivers, plus a hex key for set screws
- Replacement washers, O-rings, or the correct cartridge for your model
- Plumber’s grease and plumber’s tape
- White vinegar for dissolving mineral buildup
- A rag and a bucket
Take the old part to the hardware store to match it exactly, or note the faucet’s brand and model number, often stamped on the body or found in the original paperwork.
Step-by-Step: Fixing a Dripping Spout
- Shut off the water at the valves under the sink, then open the faucet to drain the line and relieve pressure. Plug the drain so small parts do not fall in.
- Remove the handle. Pop off the decorative cap, remove the screw or set screw, and lift the handle off.
- Access the worn part. For compression faucets, unscrew the packing nut and lift out the stem to reach the washer at the bottom. For cartridge faucets, pull the retaining clip and slide out the cartridge.
- Inspect and replace. Swap the worn washer, O-ring, or cartridge for an exact match. Clean any mineral buildup on the valve seat with vinegar; a badly pitted seat may need resurfacing or a seat replacement.
- Grease and reassemble. Coat new O-rings with plumber’s grease, reinstall parts in reverse order, and hand-tighten firmly without over-torquing.
- Turn the water back on slowly and check for leaks and smooth operation.
Most spout-drip repairs take 20 to 45 minutes and cost only a few dollars in parts.
Fixing Base and Under-Sink Leaks
For a leak around the spout base, remove the handle and spout, replace the O-rings where the spout meets the body, grease them, and reassemble. For under-sink leaks, first tighten the compression nuts on the supply lines by hand plus a quarter turn with a wrench. If the connection still weeps, replace the supply line, they are inexpensive braided-steel hoses, and wrap the threaded fittings with plumber’s tape before reconnecting. Inspect the shutoff valves too; a valve that drips at the packing nut can often be snugged up, but a corroded valve should be replaced.
What It Costs
- Washers and O-rings: $2 to $10.
- Replacement cartridge: $10 to $40 depending on brand.
- New supply lines: $5 to $15 each.
- Plumber’s service call: $125 to $350 for professional repair.
Given that parts cost so little, the DIY savings are significant. Many faucet brands, including Moen and Delta, offer lifetime warranties and will ship replacement parts free if you contact them, so check before buying.
When to Call a Plumber
Handle most drips yourself, but call a professional if you find corroded or seized shutoff valves that will not turn, water damage or mold under the cabinet, a cracked faucet body, or a leak you cannot locate after replacing the obvious parts. Persistent leaks after a full cartridge replacement can indicate a worn valve seat or a faucet at the end of its life, in which case replacing the whole faucet, typically $150 to $400 installed, makes more sense than chasing parts.
How to Repair by Faucet Type
Because each design leaks differently, here is a quick map from faucet type to likely fix.
- Compression: Almost always a worn rubber washer or a corroded valve seat. Replace the washer and, if the seat is pitted, install a new seat or dress it with a seat-grinding tool.
- Cartridge: Replace the cartridge as a unit. This single part usually cures both spout drips and handle stiffness.
- Ball type: Buy a ball-faucet repair kit with new springs, seats, cam, and O-rings, since several small parts wear together.
- Ceramic disc: Replace the rubber seals under the disc cartridge, or the whole cartridge if the discs are scored. Clean out mineral sediment while you are in there.
Matching the fix to the mechanism prevents the frustrating cycle of replacing the wrong part and still hearing a drip.
Hard Water and Mineral Buildup
In many homes, the real villain behind recurring leaks is mineral scale. Hard water deposits calcium and lime on valve seats, cartridges, and aerators, which prevents seals from seating fully and causes both dripping and reduced flow. When you disassemble the faucet, soak the metal internal parts and the aerator in white vinegar for 20 to 30 minutes to dissolve the crust, then scrub gently with an old toothbrush. If your home has very hard water, this buildup will keep coming back, so consider a whole-house water softener or at least plan to clean the aerator and internals a couple of times a year. Addressing the water quality often extends the life of every faucet, showerhead, and appliance in the house, not just the one that is currently dripping.
Preventing Future Leaks
Do not over-tighten handles; forcing them to shut off a drip only crushes and destroys washers faster. In hard-water areas, periodically clean mineral buildup from the aerator and internal parts with vinegar. And when you do a repair, replace all the washers and O-rings in the assembly at once rather than just the one that failed, since the others are usually close behind. A little preventive care keeps that maddening midnight drip from ever coming back.
It also helps to know your faucet before trouble strikes. Jot down the brand and model number, keep the original installation paperwork, and note whether the internals are compression, cartridge, ball, or ceramic disc. With that information on hand, the next repair becomes a quick trip for the exact part rather than a guessing game at the store. And remember the bigger picture: a single dripping faucet wastes thousands of gallons a year and can stain the sink or damage the cabinet below, so treating even a slow drip promptly protects both your water bill and your home. For most homeowners, a $10 repair kit and half an hour of work is all it takes to silence the drip for good.
