Leak under the sink (Troubleshooting Guide)

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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 under the sink for wet areas or dripping, and check connections. Tighten loose fittings or replace worn washers and O-rings. If the leak persists, call a plumber.

Confirm the symptom

Water pooling under the sink
Dripping sound from under the sink
Wet or damp cabinet floor
Musty smell from sink area
Low water pressure in sink

Tools and prep

Adjustable wrench
Plumber's putty or Teflon tape
Bucket or towel to catch water
Flashlight for inspection
Replacement washers or O-rings
Shut-off wrench for water valves
Safety gloves and goggles

Step-by-step troubleshooting

Turn off the water supply
Do: Locate and turn off the shut-off valves under the sink. If unavailable, turn off the main water supply.
Observe: Water stops flowing from the faucet.
Means: You can safely work on the plumbing without water pressure.
Next: Inspect the area for the source of the leak.
Inspect the area
Do: Use a flashlight to look for wet areas, dripping, or corrosion around pipes, fittings, and the drain.
Observe: Identify the exact location of the leak.
Means: Pinpoints the source for targeted repairs.
Next: Check connections and fittings.
Check connections and fittings
Do: Use an adjustable wrench to gently tighten any loose connections or fittings.
Observe: Leak stops or reduces.
Means: Loose connections were the cause.
Next: If the leak continues, check for worn washers or O-rings.
Check for worn washers or O-rings
Do: Inspect the faucet base, aerator, and connections for damaged or worn washers and O-rings.
Observe: Visible damage or wear on seals.
Means: Seals need replacement.
Next: Replace the damaged washers or O-rings.
Replace washers or O-rings
Do: Remove the affected part, replace the old washer or O-ring with a new one, and reassemble.
Observe: Leak stops after reassembly.
Means: The replacement fixed the issue.
Next: Test the repair.
Test the repair
Do: Turn the water supply back on and check for leaks.
Observe: No water leaks from the repaired area.
Means: The repair was successful.
Next: Monitor for recurring leaks.

Common causes

Cause	Likelihood	Difficulty	Part often needed
Loose pipe connections Vibrations or age can loosen fittings, causing water to leak.	Common	Easy	Wrench
Worn washers or O-rings Over time, seals degrade and no longer create a tight seal.	Common	Easy–Medium	Washer/O-ring kit
Corroded or damaged pipes Mineral buildup or corrosion weakens pipes, leading to leaks.	Sometimes	Medium	Pipe repair kit or replacement pipe
Faulty faucet cartridge A damaged or worn faucet cartridge can cause water to leak from the spout or base.	Sometimes	Medium	Faucet cartridge
Clogged or damaged P-trap Debris buildup or physical damage can cause the P-trap to leak.	Sometimes	Medium	P-trap or plumber's putty
Leaking water supply line Cracks or corrosion in the supply line can cause water to leak.	Rare	Hard	Replacement supply line

Parts matching

Common parts needed for a leak under the sink repair include:

Adjustable wrench for tightening connections
Plumber's putty or Teflon tape for sealing threads
Washer/O-ring kit for sealing fixtures
Faucet cartridge for internal faucet leaks
Pipe repair kit or replacement pipe for damaged sections
P-trap for drain connections

Purchase a basic plumbing repair kit that includes common seals and tools for quick fixes.

When to call a professional

The leak continues after tightening all connections and replacing seals
You find corroded or damaged pipes that require replacement
You're unable to locate the source of the leak
The water supply line is leaking and needs professional repair
You're unsure about the repair process or lack the necessary tools

FAQ

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

Turn off the hot water valve and check if the leak stops. If it does, the hot water line is the source. Repeat for the cold water line.

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 pipes for a permanent repair.

Why is my sink leaking even after I tightened everything?

If tightening didn't stop the leak, the issue may be a worn washer, damaged O-ring, or a crack in the pipe or fitting.

How often should I check for leaks under the sink?

Inspect under the sink at least once a month to catch leaks early and prevent water damage.