Water Leak Under the 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

Turn off the water supply to the sink. Inspect under the sink for visible leaks. Tighten loose connections or replace worn-out washers and O-rings. If the leak persists, call a plumber.

Confirm the symptom

Damp or wet area under the sink
Puddles of water near the sink base
Dripping sound when the sink is not in use
Musty odor from under the sink
Discolored cabinetry near the sink

Tools and prep

Adjustable wrench
Plumber's putty or Teflon tape
Bucket or towel to catch water
Replacement washers or O-rings
Screwdriver
Turn off water supply to the sink before starting
Wear gloves to protect hands from sharp edges and water

Step-by-step troubleshooting

Turn Off Water Supply
Do: Locate and turn off the shut-off valves under the sink.
Observe: Water stops flowing from the sink faucet.
Means: Water supply is safely cut off.
Next: Inspect for Leaks
Inspect for Leaks
Do: Check under the sink for visible leaks or moisture.
Observe: Identify the source of the leak (e.g., pipe connections, faucet base).
Means: You know where to focus repairs.
Next: Tighten Connections
Tighten Connections
Do: Use an adjustable wrench to tighten loose pipe connections.
Observe: Leak stops or reduces.
Means: Loose connections were the cause.
Next: Check for Damaged Seals
Check for Damaged Seals
Do: Inspect washers, O-rings, and gaskets for wear or damage.
Observe: Seals show cracks, deformation, or wear.
Means: Replace damaged seals to stop the leak.
Next: Replace Faulty Parts
Replace Faulty Parts
Do: Replace worn washers, O-rings, or damaged pipes as needed.
Observe: Leak stops after replacement.
Means: Faulty parts were the cause.
Next: Test the Fix
Test the Fix
Do: Turn the water supply back on and check for leaks.
Observe: No water leaks are present.
Means: Repair was successful.
Next: Done

Common causes

Cause	Likelihood	Difficulty	Part often needed
Loose Pipe Connections Over time, vibrations or temperature changes can loosen fittings.	Common	Easy	Wrench
Worn-Out Washers or O-Rings Seals degrade from constant use and water exposure.	Common	Easy	Washer/O-Ring Kit
Cracked or Corroded Pipes Old or low-quality pipes can develop cracks or corrosion.	Sometimes	Medium	Pipe Replacement Kit
Faulty Faucet Installation Improper installation can lead to leaks at the base or connections.	Sometimes	Easy–Medium	Faucet Seal Kit
Clogged Drainpipes Debris buildup can cause water to back up and leak.	Rare	Medium	Plunger or Drain Snake
High Water Pressure Excessive pressure can stress pipes and connections.	Rare	Hard	Pressure Regulator

Parts matching

Common parts needed to fix a water leak under the sink include:

Adjustable wrench for tightening connections
Plumber's putty or Teflon tape for sealing threads
Washer and O-ring kits for replacing seals
Pipe replacement kit for damaged sections
Faucet seal kit for faulty faucet installations
Plunger or drain snake for clearing clogs

Purchase a basic plumbing repair kit that includes common seals and tools to handle most minor leaks.

When to call a professional

Leak continues after replacing all visible seals and parts
Pipes are severely corroded or cracked beyond simple repair
Water damage is extensive or affecting surrounding areas
You cannot locate the source of the leak
High water pressure is suspected but you lack a pressure gauge

FAQ

Can a small leak under the sink cause major damage?

Yes, even a small leak can lead to mold growth, wood rot, and structural damage over time. Address it promptly.

How often should I check for leaks under the sink?

Inspect under the sink every few months, especially after heavy use or temperature changes.

Is it safe to use plumber's putty on all types of pipes?

Use plumber's putty only on metal pipes. For plastic pipes, use Teflon tape or appropriate sealant.

Can I fix a leak under the sink without turning off the main water supply?

It's safer to turn off the water supply to the sink using the shut-off valves. If those are unavailable, turn off the main water supply.

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

This often indicates a problem with the faucet cartridge or valve seat. Inspect and replace these parts if worn or damaged.