Water Inside Cabinet Under Sink
Water inside a cabinet under a sink can come from the supply lines, the drain, the P-trap, or the faucet base. This can sometimes indicate a loose supply line connection, a leaking drain slip nut, a corroded trap, or a failed faucet O-ring. Most under-sink leaks are repairable and don't require a full pipe replacement.
- —Loose or deteriorated supply line connection (the braided hoses under the sink)
- —Leaking P-trap slip nut or corroded trap
- —Leaking drain tailpiece or basket strainer (kitchen)
- —Faucet base leak — water running down the faucet stem under the deck
- —Garbage disposal leaking from the mounting flange or body (kitchen)
Try This First
Safe, simple steps you can try yourself. If any step feels beyond your comfort level, skip it and continue below.
- 1
Dry everything and watch
Wipe the cabinet completely dry. Run the faucet and watch where the water appears. Is it from the supply lines (above), the drain (below), or the faucet base (from above through the deck)?
- 2
Check the supply line connections
Feel the braided supply lines where they connect to the shutoff valves and the faucet. Tighten by hand — if they're already tight and still dripping, the washer inside may be worn or the line needs replacing.
- 3
Check the P-trap and drain
Place a dry paper towel under the P-trap and drain connections. Run water. If the towel gets wet, a slip nut is loose or the trap is corroded. Hand-tighten the slip nuts; if that doesn't work, the trap may need replacing.
- 4
Check the faucet base
If water appears from under the faucet (not from the supply lines or drain), the faucet's O-rings or mounting gasket may be failing. This usually requires removing the faucet to repair.
If the problem is resolved
If tightening a supply line connection or a slip nut stops the leak, you've fixed it. Replace the supply lines if they're more than 10 years old — braided lines don't last forever.
If the problem persists
If the leak is from a corroded trap, a failed faucet base, or a garbage disposal, the part needs replacing. Continue below.
Stop and Call a Plumber If…
- Tightening connections doesn't stop the leak
- The P-trap is corroded and crumbling
- The faucet is leaking from the base (needs removal and repair)
- The garbage disposal is leaking from the body or mounting flange
- The cabinet floor is water-damaged or soft
- ✓Replacing corroded or leaking P-traps and drain assemblies
- ✓Replacing supply lines with new braided stainless lines
- ✓Repairing or replacing a faucet with a failed base seal
- ✓Replacing a leaking garbage disposal
- ✓Checking for hidden water damage in the cabinet and subfloor
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Reviewed by Paul Hall, Owner & Licensed Plumber
The Classic Plumber · Knoxville, TN · License #4268. This guidance is general — an onsite inspection may be required for a confirmed diagnosis.