THE SHORT ANSWER
If the cabinet stays dry between uses but drips when water drains, the drain assembly is a useful place for a plumber to start. Timing is a clue—not proof. Water can travel along a pipe from a higher connection.
Before you try anything
Stop using the sink once a leak is known. If water is near an outlet, disposal, dishwasher connection, or any electrical equipment, stay clear and get professional help. Do not reach into a wet cabinet or recreate the leak for a better photograph.
Before you begin
A visible, small under-sink drip, with a dry floor and no nearby electrical hazard. This guide helps you document the leak; it does not cover pipe removal, concealed leaks, garbage disposals, or pressurized repairs.
A flashlight, a phone for a photo from a dry position, and a note of when the drip first appeared. No tools are needed for these observations.
In a rental, report the problem to your landlord or property manager before making repairs. Building rules and local requirements vary.
Work through the checks
- 01
Start with the timing you already observed
Write down whether the drip appeared while the faucet was on, just after a full basin emptied, or while the sink was unused. Include whether the dishwasher had just drained. Do not run extra water to reproduce a known leak.
- 02
Look from outside the cabinet
If the area is dry and safe to approach, use a flashlight without touching fittings. Note the highest visible wet point, the pipe or hose it sits on, and any staining. A drop at the bottom of a bend may have traveled there from above.
- 03
Separate the locations in your notes
The drain runs down from the basin. Smaller supply lines lead toward the faucet. Identify these only visually; do not loosen anything. If you cannot distinguish them, a wide photograph is more useful than a guessed diagnosis.
- 04
Limit further damage without working on the pipe
Keep the fixture out of use. If there is no electrical exposure and the floor is dry, move dry stored items away from the drip. Do not rely on a bucket as a repair. Tell your landlord or a plumber about active leakage promptly.
What your result means
These observations help choose a next step. They do not confirm a diagnosis.
| What you notice | What it tells you | Next step |
|---|---|---|
| Only during or just after draining | Drain-side involvement is possible. | Keep the sink out of use; share the timing and a wide photo. |
| Also drips when the sink is unused | A supply-side leak or another source is possible. | Arrange prompt plumbing help. Do not force a stuck shutoff valve. |
| Wet cabinet, but no visible origin | Water may be tracking from above or behind. | Stop testing. A concealed source needs inspection. |
Know what happens next
Check the outcome
After a qualified repair, follow the plumber’s return-to-use guidance. Check the accessible cabinet for fresh moisture during normal use and record any recurrence. A dry surface once does not establish that the underlying leak is fixed.
When to call a professional
Contact a plumber for active leaks, corrosion, damaged fittings, or an uncertain source. Notify a landlord before repairs in a rental. Water from a ceiling, major flow, or water near electrical equipment needs urgent professional assessment.
Take useful notes with you
A short record makes it easier to explain the problem to a landlord, technician, or responder. Do not collect notes during an emergency.
Notes stay in this page until you leave or reload. Download a copy to keep them. They are not sent to us.
Common questions
Should I tighten the fitting?
Not based on a photo or a drip location alone. Fitting types and seals differ, and tightening the wrong connection can create another leak. Have the source identified first.
Does a drain-only leak mean the supply lines are fine?
No. It narrows the observation but does not rule out water traveling from another location.
Sources & scope
This is a desk-researched guide, not a hands-on test or an on-site diagnosis. A licensed tradesperson has not independently reviewed this edition. Follow your product’s manual and local requirements.
- Moen: leaking under the sink base
Supports distinguishing the frequency and visible location of a leak. Product-specific repair instructions are not generalized here.
- EPA WaterSense: home maintenance
Supports checking for visible water at under-sink connections and addressing leaks.
Published 2026-09-24 · Our editorial policy · Report a correction