Under Sink Pipe Leaking (Troubleshooting Guide)

On this page

Quick answer
Confirm the symptom
Tools and prep
Step-by-step troubleshooting
Common causes table
Parts matching
When to call a pro
FAQ
Related guides

Quick answer

Turn off the water supply, inspect the leak, and tighten or replace faulty parts. Common fixes include tightening connections, replacing washers, or fixing the aerator.

Confirm the symptom

Water dripping from under the sink
Visible moisture on pipes or fixtures
Increased water bill without usage change
Standing water near the sink base
Corrosion or rust on pipe connections

Tools and prep

Adjustable wrench or pliers
Replacement washers or O-rings
Plumber's tape (Teflon tape)
Bucket or towel to catch water
Flashlight for better visibility
Turn off water supply before starting
Protective gloves and eyewear

Step-by-step troubleshooting

Shut Off Water Supply
Do: Turn off the shut-off valves under the sink.
Observe: Water stops flowing from the faucet.
Means: Water supply is safely cut off.
Next: Inspect the leak
Inspect the Leak
Do: Use a flashlight to locate the exact source of the leak.
Observe: Identify if the leak is at a connection, valve, or pipe.
Means: You know where to focus repairs.
Next: Tighten connections
Tighten Connections
Do: Use an adjustable wrench to gently tighten any loose connections.
Observe: Leak reduces or stops.
Means: Loose fittings were the issue.
Next: Check for improvement
Check for Improvement
Do: Turn on the water supply slightly to test.
Observe: Leak persists or stops.
Means: Tightening may be sufficient or further action needed.
Next: Replace washers or O-rings
Replace Washers or O-rings
Do: Remove the faulty part and install new washers or O-rings.
Observe: Leak stops after replacement.
Means: Worn seals were causing the leak.
Next: Reassemble and test
Reassemble and Test
Do: Reassemble the fixture and turn on the water supply fully.
Observe: No leaks and normal water flow.
Means: Repair is successful.
Next: Monitor for recurring issues

Common causes

Cause	Likelihood	Difficulty	Part often needed
Loose connections Vibrations or infrequent use can loosen fittings over time.	Common	Easy	None
Worn washers or O-rings Seals degrade with age and use, leading to leaks.	Common	Easy–Medium	Washer/O-ring kit
Corroded or damaged pipes Mineral buildup or rust weakens pipe integrity.	Sometimes	Medium	Pipe repair sleeve or replacement pipe
Faulty shut-off valve Internal damage or wear in the valve prevents proper sealing.	Sometimes	Medium	Shut-off valve replacement kit
Leaking aerator Screen or internal components in the aerator can become clogged or damaged.	Sometimes	Easy	Aerator
Improper installation Incorrect assembly during installation can cause leaks.	Rare	Medium	New fixture or proper installation guide
High water pressure Excessive pressure can stress connections and cause leaks.	Rare	Hard	Pressure regulator

Parts matching

Common parts needed for under sink pipe leaks include:

Washer/O-ring kit for faucet connections
Plumber's tape for sealing threaded connections
Pipe repair sleeve or replacement pipe section
Shut-off valve replacement kit
Aerator for the faucet

Purchase a basic plumbing repair kit to cover common issues like this.

When to call a professional

Leak continues after replacing washers and tightening connections
Visible cracks or severe corrosion in the pipes
Unable to locate the source of the leak
Water damage is spreading or causing mold
Multiple leaks in the plumbing system
High water pressure causing repeated leaks

FAQ

How do I know if the leak is from the hot or cold water line?

Check which valve shutting off stops the leak. Hot water lines are usually marked or insulated.

Can I use epoxy to fix a small pipe leak?

Epoxy can be a temporary fix for small leaks, but it's not a long-term solution. Replace damaged sections for a permanent fix.

Why does my sink leak only when the water is running?

This often indicates a faulty washer or O-ring in the faucet assembly that fails under pressure.

Is it normal for pipes to sweat under the sink?

Sweating pipes are usually due to high humidity or cold water lines. Insulate pipes to prevent condensation.

How often should I check under my sink for leaks?

Inspect monthly for early detection, especially if you notice higher water bills or musty odors.