Water Under the Kitchen Sink? How to Find the Leak

A small leak under the sink can ruin the cabinet floor and grow mold before anyone notices. It is one of the most common things we find on home watch visits. Finding the source is mostly detective work.

Track it down

1. Empty the cabinet and wipe every pipe and fitting dry.
2. Wrap a dry paper towel around each connection: the shutoff valves, both ends of each supply line, the faucet connections, the drain trap and the disposal.
3. Wait a few minutes with nothing running. A wet towel now means a pressurized line or valve: it leaks all the time.
4. Then run water down the drain. A wet towel now points to the drain trap, the sink strainer or the disposal.
5. Finally run the faucet and splash around the base. Water that shows up from above is coming from the faucet or the countertop seal.

Common culprits

• Braided supply lines that are old, kinked or corroded at the ends.
• Shutoff valves that drip at the stem, often after being turned for the first time in years.
• Loose slip nuts on the drain trap.
• A worn faucet base gasket or a failed sink strainer seal.
• A garbage disposal leaking from its body, which means it needs replacing.

What you can safely try

Hand-tighten loose drain slip nuts. If a supply line or valve is leaking, close the shutoff valve and put a bowl under it until it is repaired. Don’t force a stuck shutoff valve; old valves can break. Let the cabinet floor dry out fully, and keep an eye out for swelling or a musty smell.

When to call us

Call for leaking supply lines or shutoff valves, a leaking faucet or disposal, or a cabinet floor that is soft or stained. We handle under-sink plumbing repairs and can check for water damage while we are there.

Last reviewed November 1, 2026. This guide is general information. When in doubt, or for anything involving gas, wiring or major water damage, call a professional.