Quick answer
Water under a kitchen sink usually comes from a supply line or shut-off valve, a loose drain slip nut, the dishwasher drain hose, or a disposal whose seal has failed. Empty the cabinet, lay a dry paper towel under the pipes, and run the cold tap, the drain, the dishwasher and the disposal one at a time to see which drips. If the cabinet base is soft or swollen, check the floor under it, because the water may have run under the cabinets. Call (888) 840-6512 to reach a certified water damage restoration company in your area; the line is answered 24/7.
Written & reviewed by Marcus ReedIICRC WRT
Reviewed September 30, 2026· Next review Mar 2027
The cabinet under a kitchen sink is a dark box full of joints that are rarely looked at. A drip there can run for months, soaking the cabinet floor and then the subfloor under it, before anyone notices a warped panel or a smell. The fix is usually one slip nut or one supply line. The question is how much of the cabinet and the floor underneath has to be dried or replaced.
What to Do Now
- 1Empty the cabinet and dry the surface. Take everything out, wipe up the water, and lay a dry paper towel on the cabinet floor so you can see fresh drips.
- 2Find the leak by running each thing on its own. With the cabinet empty, test the joints one at a time as described below. A dry paper towel under each joint shows which one drips.
- 3Stop it at the valve or the joint. Close the shut-off valves under the sink if a supply line is leaking. Hand-tighten a drain slip nut a quarter turn if that is the drip. Replace a supply hose that is bulging or corroded.
- 4Check under the cabinet floor. Press the cabinet base, look at the toe kick, and check the ceiling below if the kitchen is upstairs. A soft or swollen base means the water has gone through.
Finding Which Joint Leaks
Run the tests in this order, with a dry towel under the pipes each time:
| Test | If it drips | Likely source |
|---|---|---|
| Nothing running, taps off | Water on the towel anyway | Supply line, shut-off valve, or the faucet's own hoses |
| Run the cold tap only | Drips at the faucet base or hoses | Faucet cartridge or connection |
| Fill the sink and let it drain | Drips at the drain pipes | Slip nuts, the trap, or the basket strainer seal |
| Run the dishwasher | Water near the disposal or drain | Dishwasher drain hose connection |
| Run the disposal | Drips from the bottom of the disposal | Disposal seal failed; the unit is usually replaced |
A leak that only appears when the dishwasher runs is common, because the dishwasher pushes water into the sink drain under pressure. The dishwasher leak guide covers the other places that water can go.
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Reading the Cabinet
Most kitchen sink bases are particleboard or MDF with a thin laminate skin. When that board gets wet, it swells and does not shrink back.
- Stained but flat and firm: it got wet and dried. Fix the leak and watch it.
- Swollen, soft or flaking at the edges: the board has failed. It can be covered with a cabinet mat, or the base panel replaced.
- A musty smell or dark spots: it has been wet long enough to grow. The mold under the kitchen sink page covers cleaning versus replacing.
When the Floor Under the Cabinet Is Wet
Cabinets sit directly on the subfloor, and the toe kick hides the gap. Water that got through the cabinet base runs under the cabinet run, under the dishwasher, and sometimes under the flooring in front of it. None of that dries on its own, because nothing moves air through a sealed cabinet. Wet wood and drywall start growing mold in about 24–48 hours.
A restoration company checks this with a moisture meter through the toe kick and the floor in front of the sink. If the subfloor is wet, the usual method is drilling small holes in the toe kick and blowing dry air under the cabinets, so the cabinets can often stay. Clean-water drying runs around $3–$7 per square foot.
If the cabinet base is soft or the floor in front of the sink has lifted, (888) 840-6512 is answered 24/7 and connects you with a certified restoration company that serves your area. The company gives you an arrival window for your address on the call, and there is no charge for the referral.
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Frequently Asked Questions
Why is there water under my kitchen sink?
The usual sources are a supply line or shut-off valve, the faucet's own hoses, a loose slip nut on the drain, the dishwasher drain hose where it joins the sink drain or disposal, and a disposal that has failed at the bottom seal.
Why does my sink only leak when the dishwasher runs?
The dishwasher pumps its water into the sink drain or the disposal under pressure. A loose clamp on the drain hose, a cracked hose, or a partly blocked drain that backs up are the usual causes.
Can a water-damaged sink cabinet be fixed?
If the base is stained but firm and flat, it only needs the leak fixed. Particleboard that has swollen or gone soft does not recover, so the base panel is replaced or covered with a cabinet mat. Any mold is cleaned or the panel removed.
Does water under the sink damage the floor?
It can. Cabinets sit directly on the subfloor, and water that gets through the cabinet base runs under the cabinet run and sometimes under the flooring in front. It does not dry on its own inside a closed cabinet.
How do I dry the floor under kitchen cabinets?
Restoration crews usually drill small holes in the toe kick and blow dry air under the cabinets, checking the subfloor with a moisture meter until it reads dry. The cabinets can often stay in place.
Who do I call right now for water damage?
Call (888) 840-6512. The line is answered 24 hours a day, seven days a week, and connects you with an IICRC-certified water damage restoration company that serves your area. Describe what you can see — where the water is coming from, how long it has been there, and whether it smells — the more specific you are, the faster the right company is on the line.
If the source is a pipe or an appliance, shut the main water valve first. Have four things ready and the call goes quickly: the address, when the water started, what is wet now, and whether you have filed an insurance claim.
Still not sure which of these is your situation? (888) 840-6512 · toll-free · answered 24/7
Sources
- IICRC S500 Standard for Professional Water Damage Restoration
- EPA — A Brief Guide to Mold, Moisture and Your Home
Methodology: How we source and verify data · Report an error
Disclaimer: HearthDry is an independent educational resource. This article is for informational purposes only and does not constitute professional, legal, or insurance advice. Consult licensed professionals before making decisions about your property or insurance claims.
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