How to diagnose and stop a slow under-sink leak before it rots your subfloor

A tiny drip beneath your kitchen or bathroom vanity can go undetected for months until you step on a squishy floorboard or smell mildew.

Here are the 4 main places water sneaks out and how to check them in 5 minutes:

1. Supply line nut tension: Give each braided stainless steel line a wipe with a dry paper towel. If it comes back damp, the rubber gasket inside the compression fitting has compressed or dried out. A quarter turn with a basin wrench usually seals it without stripping the threads.

2. Escutcheon drain slip joint: Under the sink basket, the P-trap slip nuts vibrate loose from garbage disposal vibrations. Unscrew, clean the beveled plastic washer, inspect for hairline cracks, and hand-tighten plus 1/2 turn.

3. Spray hose retraction weight: If your pull-down faucet hose frays, water runs down the braided sleeve inside the cabinet every time the sprayer is engaged. Look for water pooled near the cast iron ballast weight.

4. Faucet body gasket: If water pools around the faucet base on top of the counter, deteriorated silicone or foam gaskets let soapy dish water seep down underneath.

Pro tip: Place a battery-powered $12 moisture alarm on the cabinet floor behind the P-trap. It has saved multiple neighbors thousands of dollars in mold remediation!