Quick Answer:
If the overflow hole is dripping constantly, it usually means water is finding a path into the overflow channel. That can come from a slow faucet leak, a filling issue, or a problem inside the overflow channel itself. Start with simple checks at the sink and dry the opening to confirm whether the drip is ongoing before doing anything more invasive.
Why This Happens
- Slow faucet or cartridge leaks let water trickle into the overflow rather than down the drain.
- A blocked or partially blocked channel can hold water and make it look like a continuous drip even after the source stops—see Overflow channel blocked by buildup.
- Cracks or loose connections under the sink can let water enter the channel and drip into the cabinet—see Overflow channel leaking inside cabinet.
- Condensation from cold water or brief splashes can also keep the channel wet, but a true continuous drip usually points to a leak.
Step-by-Step What to Do
1. Confirm it’s actually dripping
Dry the overflow opening and check again 30 minutes later to confirm it is an ongoing drip. Use a tissue or paper towel and mark the spot so you can tell if fresh water appears.
2. Isolate obvious sources
- Turn off the faucet and watch for the drip. If the drip stops, the faucet or cartridge is the likely source.
- Run water and fill the basin to see if the drip begins only when the sink is full or while the drain is running.
3. Check faucet and handles
Look for slow leaks from the faucet spout or around handles. A worn cartridge, O-ring, or valve seat can leak slowly and route water into the overflow channel. If you’re comfortable, tighten visible fittings gently; otherwise leave repairs to a pro.
4. Inspect the overflow channel and underside of the sink
- Open the cabinet and look for water stains, damp insulation, or active dripping under the sink.
- Use a flashlight to inspect the overflow path for mineral buildup or foreign material.
5. What you can try safely at home
- Wipe the overflow channel dry and test again later to confirm persistence (as above).
- If you see mineral buildup near the overflow inlet, gently clean the opening with a soft brush and water. Avoid harsh chemicals that can damage finishes or plumbing parts.
- Place a dry container or towel under the sink to catch any drips while you monitor.
6. When to stop and call for help
If you find water tracking from an unseen source, continuous wetness inside the cabinet, or you can’t identify the leak after these checks, it’s time to call a plumber. Do not take apart plumbing you’re not trained to fix — that can make a small leak into a bigger problem.
What Not to Do
- Do not ignore constant dripping—continuous moisture can lead to mold inside the cabinet.
- Do not use strong drain or overflow chemicals in an attempt to clear an overflow channel while water is pooling under the sink; chemicals can damage pipes and finishes and create hazardous fumes.
- Do not remove or cut plumbing components unless you have the right tools and experience—improper reassembly can cause larger leaks.
When to Call a Professional
- There is active dripping into the cabinet that you can’t locate or stop.
- You see mold, widespread water damage, or soft/stained wood under the sink.
- The drip continues after replacing or tightening visible faucet parts, or if the leak appears to be inside the sink body or overflow channel.
- You’re unsure how to disassemble faucet cartridges or drain connections safely.
Safety Notes
- Turn off water supply valves before attempting any repairs that involve disconnecting parts.
- Avoid using harsh chemical cleaners where water has pooled; they can create toxic fumes and damage materials.
- If you see electrical devices or outlets near the leak, switch off power to that area before working under the sink and avoid standing water.
- If mold is present or the cabinet has been wet for a long time, consider professional remediation for safe cleanup.
Common Homeowner Questions
- Why did this start suddenly?
Small parts like cartridges and O-rings can wear out over time; a sudden change in water pressure or a mineral deposit breaking loose can also start a drip. - Can I fix this myself?
Simple checks and drying/monitoring you can do yourself. Replacing faucet cartridges or correcting hidden leaks is best left to a plumber if you’re not experienced. - Will a slow drip cost a lot to fix?
Fix cost varies: sometimes a small part replacement is inexpensive; hidden or structural leaks that caused damage can be more costly.