You open the cabinet under the kitchen or bathroom sink and find standing water. A leak under the sink is one of the most common plumbing problems, and it is usually one of the easiest to fix. The key is identifying exactly where the water is coming from.

How to Fix a Leaky Pipe Under the Sink

Finding the Leak Source

Dry off all the pipes under the sink with paper towels or a dry cloth. Then run the water and watch carefully. The leak will appear at one of these locations:

Supply Line Connections

The flexible hoses that bring hot and cold water to the faucet connect to the shut-off valves below and to the faucet above. Leaks here appear at the threaded connections.

Fix: Turn off the water supply. Tighten the connection with pliers or a wrench — often a quarter turn is enough. If it still leaks, turn off the water, disconnect the line, wrap the threads with fresh Teflon tape (3 to 5 wraps clockwise), and reconnect.

If the supply line itself is cracked or corroded, replace it. Braided stainless steel supply lines are more durable and easier to install than rigid chrome tubes.

P-Trap Connections

The P-trap is the curved pipe section that holds water to block sewer gas. It connects to the drain tailpiece (dropping from the sink) and the drain pipe (going into the wall). Slip-joint nuts hold these connections together with compression washers.

Fix: Hand-tighten the slip-joint nuts. If hand-tight does not seal, use pliers for a quarter turn. Do not over-tighten plastic fittings — they crack.

If tightening does not stop the leak:

Unscrew the slip-joint nuts and pull the P-trap off
Check the compression washers (thin plastic or rubber rings) for cracks, deformation, or improper seating
Replace worn washers — they cost pennies at the hardware store
Reassemble, ensuring washers seat correctly in the joints
If the P-trap itself is corroded (common with metal traps), replace the entire trap assembly with a PVC version ($5 to $10)

Drain Tailpiece

The vertical pipe dropping from the sink’s drain basket into the P-trap. Leaks at the top of this pipe (where it meets the sink drain) indicate a worn gasket or loose connection.

Fix: Tighten the slip nut connecting the tailpiece to the drain strainer. If the leak is at the strainer itself, you may need to remove the strainer, clean off old plumber’s putty, apply fresh putty, and reinstall.

Faucet Base

Water appearing around the base of the faucet and running down the back of the sink indicates worn faucet O-rings. See the faucet repair guide for this fix.

Garbage Disposal Connections

If you have a garbage disposal, check:

The connection between the disposal and the sink drain flange (tighten the mounting ring or replace the gasket)
The discharge tube where the disposal connects to the drain pipe (tighten the clamp)
The dishwasher inlet connection on the side of the disposal (tighten the clamp or replace the hose)

Emergency Temporary Fixes

If you discover a leak late at night and cannot get parts immediately:

Pipe repair tape: Self-fusing silicone tape wraps around a leaking joint and seals temporarily. It does not stick to the pipe — it sticks to itself. Keep a roll in your plumbing toolkit.

Pipe clamp: A repair clamp with a rubber gasket bolts around a leaking section of pipe. Available at hardware stores for $5 to $10.

Bucket and shut-off: In the worst case, place a bucket under the leak and turn off the water supply until you can make a proper repair.

Preventing Under-Sink Leaks

Check under sinks monthly for dampness or drips
Replace metal P-traps and supply lines proactively when they show corrosion
Do not use the space under the sink to store heavy items that can bump and loosen connections
When installing a new faucet, use quality supply lines and hand-tighten connections carefully
Run the water and check for leaks after any work under the sink before closing the cabinet

When to Call a Plumber

Under-sink leaks are almost always DIY-fixable. Call a plumber if:

The leak is from inside the wall (behind the wall pipe)
You find corroded galvanized steel pipes that need replacement
The leak involves the main drain stack
You are not comfortable working with water supply connections

A leak ignored causes wood rot, mold growth, and potentially thousands of dollars in water damage repair. Check under your sinks today.