USA Expert Plumbing

Leak under the kitchen sink: emergency fixes

By USA Expert Plumbing Editorial Team. Updated . 2 min read.

Short answer

Close the two shutoff valves under the sink, or the main water valve if they will not turn. Then dry everything and run water in short bursts to find the source: supply lines, the faucet base, the drain trap, the garbage disposal or the dishwasher connection. Loose slip nuts and worn supply lines are common, inexpensive fixes.

In this guide
  1. Stop the water
  2. Find the source
  3. Common fixes
  4. When to call a plumber
  5. What repairs usually cost
  6. Prevent the next leak

A kitchen sink cabinet hides several connections in a small space. Most leaks come from one of them, and many are simple to fix once you know which.

First step in any water emergency: close the main water shutoff valve. If water is near outlets, appliances or the electrical panel, keep clear of it and turn off power only if you can reach the breaker panel without standing in water.

Stop the water

  1. Close the hot and cold shutoff valves under the sink by turning them clockwise.
  2. If they are stuck or leaking themselves, close the main water shutoff.
  3. Empty the cabinet, put down towels and a shallow pan.

Find the source

Dry every pipe and connection with a paper towel, then test one area at a time:

  • Supply lines from the valves to the faucet: leaks show up with the valves open even when the faucet is off.
  • Faucet base or sprayer hose: run the faucet and watch from below.
  • Drain and trap: fill the sink with a few inches of water, then release it and watch the slip nuts and trap.
  • Garbage disposal: leaks from the top flange, the side dishwasher inlet or the bottom of the unit.
  • Dishwasher connection: run a short cycle and check the drain hose and supply line.

Common fixes

SourceUsual fix
Drain slip nutHand-tighten, or replace the washer
Supply lineReplace with a braided stainless line
Shutoff valve packingSnug the packing nut gently, or replace the valve
Faucet baseTighten mounting nuts or replace faucet seals
Disposal bodyA leak from the bottom of the unit usually means replacing it

When to call a plumber

  • Shutoff valves that will not close or leak when turned
  • Leaks inside the wall behind the sink
  • Cracked drain pipes or corroded metal traps
  • Water damage to the cabinet floor or subfloor

Check the cabinet floor afterward. Particleboard swells and can grow mold if it stays wet. For what repairs usually cost, see our plumber cost per hour guide.

What repairs usually cost

Most under-sink fixes are small jobs: a new supply line, a slip nut washer or a replacement trap. Replacing a shutoff valve, a faucet or a garbage disposal costs more, and water damage to the cabinet or subfloor adds to the bill. A plumber can often fix several small issues on one visit.

Prevent the next leak

  • Replace rubber supply lines with braided stainless ones every several years.
  • Keep a small leak sensor or a tray in the cabinet.
  • Do not store heavy items that can knock pipes loose.
  • Turn the shutoff valves once a year so they do not seize.

Common questions

Why is water under my sink only when the dishwasher runs?

The dishwasher drain hose or its connection to the disposal or drain is the likely source.

Can I use plumber's tape on a leaking slip nut?

Slip nuts seal with a washer, not thread tape. Replace the washer instead.

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