How to Fix a Leaky Sink: Find and Stop the Leak

A leaky sink can waste water and damage the cabinet below, but many drips come from a loose connection or a worn, replaceable seal. The key is to locate the source before tightening or taking anything apart. This guide covers common faucet, drain, and under-sink leaks; if the leak is inside a wall or a pipe is badly corroded, contact a plumber.

What You’ll Need

Bucket or shallow pan, plus towels or paper towels
Flashlight and a dry tissue for tracing small drips
Adjustable wrench or the tool that fits the fastener
Screwdriver and, if appropriate, pliers
Replacement washer, O-ring, cartridge, or drain seal that matches your faucet or sink
Plumber’s putty or thread-sealing tape only if specified for the particular drain or connection

Parts vary by faucet and drain design, so take a photo of the assembly and bring the old part or its model information when buying a replacement. Do not assume tape or putty is suitable for every joint.

Step-by-Step

Protect the area. Remove items from the cabinet, put a bucket beneath the leak, and wipe the sink and plumbing dry. Keep water away from electrical devices, and do not work where water is pooling near an outlet or appliance.
Find the exact source. Turn the faucet on briefly, then off, while watching the faucet base, handles, drain opening, and pipes below. Dry each suspected spot and press a strip of tissue against it; the first fresh wet mark helps distinguish a drip from water running down from above. Check again with the faucet both running and off.
Shut off water when needed. For a faucet or supply-line repair, turn the hot and cold shutoff valves under the sink clockwise until closed. If there are no working valves, shut off the home’s main water supply. Open the faucet to release pressure and confirm the water stops. Leave drain-only work alone if it does not require opening a pressurized connection, but keep a bucket underneath.
Check the supply connections. If water appears at a shutoff valve, supply hose, or its connection to the faucet, dry it and observe where the bead forms. A connection may be loose, but do not force it: support the valve or fitting with one wrench while carefully tightening the mating nut with another. If a hose is cracked, bulging, rusty, or still leaks, replace it with the correct type rather than repeatedly tightening it.
Repair a dripping faucet. A drip from the spout when the faucet is off usually points to an internal seal, cartridge, or valve component. Identify the faucet make and model if possible, then follow its parts diagram. With water shut off, cover the drain to catch small pieces, remove the handle and retaining parts in order, and replace the matching cartridge, washer, or O-ring. Reassemble without overtightening; faucet designs differ, so do not force a component that will not seat.
Repair a leak around the faucet base. Water around the base may be runoff from a wet sink, a loose mounting nut, or a worn seal. Dry the area and test again to confirm the source. If the mounting hardware is accessible, tighten it gently from below while keeping the faucet aligned. Replace a damaged seal with the correct part; avoid smearing caulk over the leak, which can hide water rather than stop it.
Repair a drain leak. Run water into the sink and inspect the drain flange, tailpiece, and joints in the P-trap. If a slip-joint nut is damp, align the pipe and hand-tighten the nut; use pliers only for a small additional turn if needed. If water leaks at the drain flange where it meets the basin, the drain may need to be removed and resealed using the sealant recommended for that sink and drain. Do not use plumber’s putty on materials that its label says it can stain or damage.
Restore water and test. Close the faucet, reopen the shutoff valves slowly, and check every disturbed connection with dry tissue. Run cold and hot water, fill the basin partway, then release it to test the drain under flow. Check again after several minutes. Dry the cabinet and monitor it later for any returning dampness.

Common Mistakes

Tightening every joint hard: Excess force can crack plastic traps, damage threads, or distort seals. Tighten gradually and stop if a fitting resists or begins to deform.
Guessing at the source: Water can travel along a hose or pipe before dripping. Dry the area and use tissue to trace the highest fresh wet point.
Using the wrong sealant: Thread tape, plumber’s putty, and silicone are not interchangeable. Follow the drain or faucet maker’s instructions and the product label.
Replacing parts by appearance alone: Similar cartridges and washers may not fit. Match the model or take the old component to a plumbing supplier.
Ignoring a slow leak after the repair: A few drops can still damage cabinetry. Test while water is running and after the sink has drained.

Tips

Take photos as you remove parts so you can put them back in the right order.
Keep a small bowl for screws and clips, and cover the drain before disassembly.
Use two wrenches on threaded supply connections when appropriate: one to hold the stationary fitting and one to turn the nut.
Check the cabinet floor and back wall for swelling, staining, or a musty smell. Drying a small spill promptly can help limit further damage.
Replace a damaged flexible supply hose rather than trying to patch it. Make sure replacement fittings match the valve and faucet.

Troubleshooting

The leak continues after tightening: The seal may be worn, the pipe misaligned, or the fitting cracked. Shut off the water if a pressurized line is involved, then inspect and replace the defective part. Do not keep tightening.

The leak appears only when water drains: Focus on the drain flange, trap, and slip-joint connections. Pour a small amount of water into the basin while watching each joint, then test again with a fuller basin.

The faucet still drips when off: Confirm the shutoff valves are fully open after the repair and check that the replacement cartridge or washer is the correct one and properly seated. If the valve body is damaged, a plumber may need to replace or service the faucet.

A shutoff valve will not turn or begins leaking: Do not force it. If the valve cannot isolate the sink, close the main water supply and arrange a repair. A leaking or seized shutoff valve can worsen when handled.

You cannot locate the leak: Dry the cabinet and inspect with a flashlight while someone runs the faucet. If water is coming from a wall, floor, or concealed pipe, or the cabinet is already soaked, stop using the sink and call a plumber.

Frequently Asked Questions

Can I fix a leaky sink without turning off the water?

Only simple drain checks that do not open a pressurized connection may be done without shutting off the supply. Turn off the hot and cold valves before opening or replacing faucet or supply-line parts.

Why does my sink leak only when I use the faucet?

Water may escape from the drain, trap, faucet base, or a supply connection under flow. Dry the parts and observe them while running water to find the first point that becomes wet.

Should I use plumber’s tape on a leaking pipe?

Only use thread-sealing tape on threaded joints where the fitting design calls for it. It does not repair a cracked pipe, a worn washer, or a slip-joint seal, and it should not be wrapped around compression-fitting threads.

When should I call a plumber?

Call if a shutoff valve is stuck or leaking, a pipe is cracked or concealed, the leak persists after the correct part is replaced, or you are unsure how to reassemble the faucet or drain safely.

How can I tell whether the leak is from the faucet or drain?

A faucet or supply leak can show up while the tap runs or even when it is off. A drain leak typically appears when water flows through the basin or trap; dry each area and test them separately.

Further reading: U.S. Environmental Protection Agency. Details can change, so check the official page for anything that matters to you. Spotted a mistake? Tell us. How we write an answer.