Quick answer
Turn off the water supply to the sink. Check the connections under the sink for visible leaks. Tighten loose fittings or replace worn-out washers and O-rings. If the leak continues, replace the faulty part or call a plumber.
Confirm the symptom
- Water pooling under the sink
- Dripping sound when using the sink
- Wet spots on the cabinet floor
- Mold or mildew smell near the sink area
- Visible water stains on the underside of the sink
Tools and prep
- Adjustable wrench
- Plumber's putty or Teflon tape
- Bucket or towel to catch water
- Replacement washers, O-rings, or seals
- Turn off the water supply before starting
- Work in a well-ventilated area
- Wear gloves to protect your hands
Step-by-step troubleshooting
- Turn Off Water SupplyDo: Locate and turn off the shut-off valves under the sink.Observe: Water stops flowing from the faucet.Means: The water supply is successfully turned off.Next: Inspect for leaks
- Inspect for LeaksDo: Look under the sink for visible water or wet spots.Observe: Identify the source of the leak.Means: You can determine which part is causing the leak.Next: Check connections
- Check ConnectionsDo: Use an adjustable wrench to tighten any loose fittings.Observe: Leak may stop if the connection was loose.Means: The leak is likely due to a loose connection.Next: Replace seals
- Replace SealsDo: Replace worn-out washers, O-rings, or seals on the affected part.Observe: Leak stops after replacing the seals.Means: The leak was caused by a faulty seal.Next: Test the fix
- Test the FixDo: Turn the water supply back on and check for leaks.Observe: No new leaks appear.Means: The repair was successful.Next: Monitor over time
- Monitor Over TimeDo: Check the area daily for any signs of recurring leaks.Observe: Leak does not return.Means: The issue is resolved.Next: Complete
Common causes
| Cause | Likelihood | Difficulty | Part often needed |
|---|---|---|---|
| Loose Fittings Connections can loosen over time from regular use. | Common | Easy | Wrench |
| Worn-Out Washers Rubber washers degrade and lose their seal over time. | Common | Easy | Washer |
| Faulty O-Rings O-rings can crack or become misaligned, causing leaks. | Common | Easy | O-ring |
| Damaged Valve Stem A cracked or corroded valve stem can cause water to leak. | Sometimes | Medium | Valve stem |
| Cracked Pipes Pipes can develop hairline cracks from age or pressure. | Rare | Hard | Pipe replacement |
| Faulty Faucet Cartridge A worn or damaged cartridge can cause leaks. | Sometimes | Medium | Faucet cartridge |
| Corroded Supply Lines Corrosion can weaken supply lines and lead to leaks. | Rare | Hard | Supply line replacement |
Parts matching
Common parts needed for under-sink leaks include:
- Wrench for tightening connections
- Plumber's putty or Teflon tape for sealing threads
- Replacement washers and O-rings
- Faucet cartridge for cartridge-style faucets
- Valve stem for leaky valves
- Pipe repair kit for minor cracks
Purchase parts that match your sink's brand and model for compatibility.
When to call a professional
- The leak continues after replacing all seals and connections
- You notice a strong smell of gas or suspect a gas line leak
- The pipes are severely corroded or cracked
- You're unsure about the source of the leak
- The water pressure is consistently low after the repair
- The repair requires cutting into walls or floors
FAQ
How do I know if the leak is from the faucet or the pipes?
Check the faucet first for visible leaks or dripping. If the leak persists when the faucet is off, it's likely from the pipes or valves under the sink.
Can I use epoxy to fix a small crack in a pipe?
Epoxy can be a temporary fix for small cracks, but it's not a permanent solution. Replace the damaged section of the pipe for a lasting repair.
Why is my sink leaking only when I turn on the hot water?
A hot water leak often indicates a problem with the hot water valve or cartridge. Check and replace the affected part.
How often should I check for leaks under the sink?
Inspect under the sink at least once a month for early signs of leaks to prevent water damage.
Can a leak under the sink cause mold?
Yes, water pooling under the sink can lead to mold and mildew growth. Fix the leak promptly to prevent this.