Plumbing Leaks Under Sink (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

First, turn off the water supply valves under the sink. Place a bucket to catch water. Check for visible leaks and tighten any loose connections. If the leak persists, you may need to replace a component.

Confirm the symptom

Water pooling under the sink
Damp or wet cabinets
Musty odors under the sink
Visible water stains on the floor
Water dripping when faucet is off

Tools and prep

Adjustable wrench
Screwdrivers (flathead and Phillips)
Bucket and towels
Flashlight
Pipe wrench
Plumber's tape
Replacement parts (if needed)
Turn off water supply valves under the sink

Step-by-step troubleshooting

Locate the Leak
Do: Inspect the area under the sink with a flashlight.
Observe: Identify the source of the leak.
Means: Check connections to the faucet, supply lines, and drain pipe.
Next: Tighten Loose Connections
Tighten Loose Connections
Do: Use an adjustable wrench to tighten any loose connections.
Observe: Ensure connections are secure but not over-tightened.
Means: Check supply lines and drain pipes.
Next: Check for Damage
Check for Damage
Do: Inspect pipes and connections for cracks or damage.
Observe: Look for signs of corrosion or wear.
Means: Replace damaged parts if necessary.
Next: Replace Washers or O-Rings
Replace Washers or O-Rings
Do: If leaks are due to worn-out washers or O-rings, replace them.
Observe: Ensure new parts are properly installed.
Means: Use plumber's tape to secure new parts.
Next: Test the Repair
Test the Repair
Do: Turn the water supply back on slowly.
Observe: Check for any remaining leaks.
Means: Monitor the area for a few minutes.
Next: Clean Up
Clean Up
Do: Dry the area and remove any buckets or towels.
Observe: Ensure the area is dry and clean.
Means: Check for any residual water.
Next: Monitor for Future Leaks
Monitor for Future Leaks
Do: Keep an eye on the area for any signs of future leaks.
Observe: Regularly inspect the plumbing under the sink.
Means: Address any issues promptly.
Next: Done

Common causes

Cause	Likelihood	Difficulty	Part often needed
Loose Connections Connections can loosen over time due to vibrations and wear.	Common	Easy	Adjustable wrench
Worn-out Washers or O-Rings These parts can degrade over time, leading to leaks.	Common	Easy–Medium	Replacement washers or O-rings
Corroded Pipes Older pipes can corrode and develop leaks.	Sometimes	Medium	Replacement pipes
Cracked Drain Pipe Drain pipes can crack due to age or physical damage.	Sometimes	Medium	Replacement drain pipe
Faulty Faucet Internal faucet components can fail, causing leaks.	Sometimes	Medium	Faucet repair kit
High Water Pressure Excessive water pressure can strain plumbing components.	Rare	Medium	Pressure regulator
Clogged Drain A clog can cause water to back up and leak.	Rare	Easy–Medium	Drain snake or plunger

Parts matching

Ensure you have the right parts before starting the repair. Common parts needed include:

Adjustable wrench
Replacement washers or O-rings
Plumber's tape
Replacement pipes or fittings
Faucet repair kit
Drain snake or plunger

Always buy parts from reputable suppliers to ensure quality and compatibility.

When to call a professional

If the leak is severe and causing significant water damage
If you cannot locate the source of the leak
If the leak persists after attempting repairs
If you are not comfortable performing the repair yourself
If the plumbing system is old and in poor condition
If the leak is accompanied by other plumbing issues

FAQ

How do I turn off the water supply under the sink?

Locate the valves under the sink and turn them clockwise to shut off the water.

Can I use any type of plumber's tape?

Use PTFE (polytetrafluoroethylene) tape, also known as Teflon tape, for plumbing repairs.

What if the leak is coming from the drain pipe?

Check for cracks or damage. You may need to replace the affected section of the pipe.

How often should I inspect my plumbing?

Regularly inspect your plumbing at least once a year to catch issues early.