How to Find and Fix a Leak Under Your Bathroom Sink

Water under a bathroom sink is a quiet enemy that turns a small nuisance into major rot if ignored. Most leaks are not pipe failures but rather loose fittings or degraded washers that have simply reached the end of their lifespan. Successfully fixing this requires a methodical approach: clearing the space, identifying the specific drip point, and performing a dry-test. When you do it right, the cabinet floor stays bone-dry and the plumbing remains accessible for future maintenance.

1. Clear the Cabinet First. Remove all stored items to gain clear visibility. Wipe the entire surface, including all pipes and connections, completely dry with a clean rag.
2. Trace the Drip Point. Wrap a dry paper towel around each connection point, including the P-trap, slip nuts, and supply lines. Turn on the faucet and watch where the paper towel darkens first.
3. Tighten All Connections. Attempt to tighten any leaking slip nuts by hand. If they are tight and still dripping, use channel-lock pliers to give them a quarter-turn more, being careful not to crack plastic threads.
4. Swap the Gasket Out. If tightening fails, turn off the water valves, unscrew the slip nut, and remove the plastic or rubber washer. Install a new washer of the exact same size and shape.
5. Replace Supply Hoses. If the leak is at the flexible supply line connection, unscrew the nut and inspect the internal rubber gasket. If it is pinched or brittle, replace the entire supply hose.
6. Confirm the Fix Works. Turn the water back on slowly and check all repaired joints while the water is running. Leave a fresh, dry paper towel under the joint for thirty minutes to confirm the drip is gone.