How to Find and Fix a Kitchen Sink Leak

Water beneath your kitchen sink is rarely a mystery; it is almost always a slow accumulation from a loose connection or a degraded seal. When you see that moisture forming on the cabinet floor, your first priority is clearing the space and observing the plumbing while it is dry. A sink that is 'done well' is one where every joint is bone-dry and the P-trap is clear of debris. Fixing these leaks is a rite of passage for every homeowner. Most of these issues do not require a plumber; they require a bucket, a flashlight, and the patience to tighten a nut or swap a rubber washer. Approach this methodically, moving from the top down, and you will stop the water before it warps your cabinetry.

1. Clear the cabinet floor. Remove all stored items from under the sink. Wipe the pipes and the cabinet floor completely dry with a towel, as this makes it easier to spot new moisture.
2. Spot the leak source. Run the faucet at full volume while looking at every connection with your light. Check the sink drain flange, the supply lines, and the P-trap joints for any beading water.
3. Tighten the connection. If a connection at a pipe joint or supply line is weeping, use slip-joint pliers to tighten the nut a quarter-turn. Do not overtighten, as you risk cracking the plastic or stripping the threads.
4. Swap the rubber washer. If tightening does not stop the leak, shut off the water valves, disconnect the leaking joint, and remove the old washer. Install a new washer of the exact same size and material.
5. Clear the P-trap. Place a bucket under the U-shaped pipe, unscrew the slip nuts, and remove the trap. Clean out any hair or gunk trapped inside before reassembling with new washers.
6. Confirm the leak is gone. Turn your water supply back on slowly and run the faucet for two minutes. Inspect every joint again to ensure the leak is completely resolved.