Symptoms
- Puddle or wet cabinet floor under the sink
- Drip visible at a joint when running water
- Musty smell in the cabinet
- Warped or stained cabinet bottom
Likely causes
- CommonLoose slip-joint nut on the P-trapThese plastic or metal nuts can loosen from vibration or age, letting water seep at the joint.
- CommonWorn or missing washer inside a slip-joint connectionThe rubber or nylon washer that seals the joint degrades over time.
- PossibleCorroded supply line or shutoff valveOlder flexible supply lines or valves can corrode and weep at their connections.
- Less commonCracked trap or drain pipePlastic traps can crack from being over-tightened or bumped while cleaning.
What to do
- Place a bucket under the pipes and dry everything with a towel so you can see exactly where water reappears.
- Run water and watch closely to pinpoint the exact joint that's leaking.
- Hand-tighten the slip-joint nut at that location, then snug it slightly more with pliers, being careful not to overtighten plastic fittings.
- If it still leaks, disassemble the joint and check the washer inside for cracking or misalignment, replacing it if needed.
- For a leaking supply line or valve, check that the compression fitting is snug and consider replacing an old flexible line entirely.
- Reassemble, run water again, and check the same spot along with nearby joints for any leaking.
- Dry out the cabinet floor and check back over the next day to confirm the leak is fully stopped.
Tools and parts
- Adjustable pliers
- Bucket
- Towel
P-trap washer or slip-joint kitSearch: “P-trap washer replacement kit”
When to call a pro
Call a plumber if the leak is coming from a cracked pipe or you can't identify the source after checking all joints.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.