# Water leaking under the sink: find the drip and stop it

Updated: 2026-10-24 · https://pros411.com/en/guides/plumbers/water-leaking-under-sink

## Short answer

Empty the cabinet, dry every pipe and lay paper towels on the cabinet floor. With the faucet off, wipe the valves and supply lines: they are always under pressure. Then fill the sink and let it drain while you watch the drain pipes. Most leaks are a loose slip nut on the drain: hand-tighten it a quarter turn. If a valve, hose or pipe is cracked, close the water and call a plumber.

## How to find and stop a leak under the sink

![Cartoon kitchen sink cabinet with water dripping from the drain trap into a puddle](https://pros411.com/img/guias/water-leaking-under-sink.webp)

1. **Water on the cabinet floor.** Something under the sink is dripping. Put a bowl under it for now and hold off on the dishwasher until you find it.
2. **Dry everything and lay down paper towels.** Take everything out, dry the pipes with a rag and lay paper towels on the cabinet floor. A new wet spot shows exactly where it drips.
3. **Check the shut-off valves and supply lines.** They hold pressure even with the faucet off. Wipe each valve, nut and hose with a dry tissue. All dry means the leak is on the drain side.
4. **Fill the sink, then let it drain.** Drain leaks only show when water runs. Fill the sink a few inches, pull the plug and watch the pipes and the paper towel.
5. **Hand-tighten the leaking nut a quarter turn.** Plastic slip nuts crack with a wrench. Snug it by hand, dry it and test again. A dry towel means you are done.

## Where leaks hide

- Around the faucet base or the sink rim: splashes seep under and drip down. Wipe it dry and reseal with caulk.
- The drain flange, where the drain meets the sink: the putty under it dries out and has to be redone.
- The dishwasher hose or the garbage disposal: if the drip comes from the disposal, see the disposal guide.
- A braided supply line that is rusty, kinked or bulging: replace it before it bursts.

## What not to do

- Do not wrap the leak in tape and forget it. The drip slows, but the cabinet floor keeps rotting.
- Do not crank plastic nuts with pliers. They crack and leak worse.
- Do not close a wet cabinet. Dry it with the doors open and a fan so mold does not start.

## When to call a plumber

- A shut-off valve, a supply hose or a metal pipe is cracked or corroded.
- It still leaks after you tighten the nut, or the trap is cracked.
- The leak comes from the drain flange under the sink basket.
- Water comes from inside the wall, or the cabinet floor is soft or moldy.

Find plumbers in your city: https://pros411.com/en/plumbers

## Frequently asked questions

### Why is there water under my kitchen sink?

Most often a loose slip nut on the drain, a leaking supply line or water seeping in around the faucet. Paper towels on the cabinet floor show you which one it is.

### How do I find where my sink is leaking from?

Dry everything, then test one part at a time. Check the supply lines with the faucet off, the drain while a full sink empties and the faucet base by splashing water on it.

### Can I use plumber tape on a leaking drain pipe?

No, thread tape does not seal slip nuts. They seal with a beveled washer inside the nut: if snugging the nut does not stop the drip, replace that washer.

### Is a slow leak under the sink an emergency?

Not usually, but fix it within days. A constant drip ruins the cabinet floor and grows mold. If a supply line sprays, close its shut-off valve right away.

### How tight should a drain slip nut be?

Hand-tight plus about a quarter turn. Plastic nuts crack if you force them with a wrench, and that makes a bigger leak.