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What Causes Water Damage Under a Kitchen Sink?

Last updated October 26, 2026

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The short answer

Common Leak Sources

The most frequent culprit is a loose or cracked supply line, the braided hose that carries water to the faucet. These connections can work loose from vibration or temperature changes, letting a steady drip escape. Another common source is the P-trap, the curved pipe under the drain, where slip nuts can loosen or the gasket can wear out.

Faucet bases also fail. The seal between the faucet and the sink can degrade, allowing water to run down the outside of the pipes and pool underneath. Dishwasher supply lines, if your dishwasher connects under the sink, can leak at the connection point. Even a slow drip from any of these spots can cause significant damage over weeks or months.

  • Loose supply line connections
  • Cracked or worn P-trap gaskets
  • Failing faucet base seal
  • Dishwasher line connection leaks
  • Corroded metal pipes
  • Improperly tightened slip nuts

Signs of Hidden Moisture

Look under the sink regularly for early warning signs. Water stains on the cabinet floor, a musty smell, or visible drips on pipes are obvious clues. You might also notice the cabinet wood feels soft or spongy, or see small dark spots that suggest mold growth. Warping or peeling of the cabinet's interior finish is another red flag.

Sometimes the leak is inside the wall behind the sink, not under the cabinet. Check the wall surface for bubbling paint, discoloration, or a slight bulge. If you notice any of these signs, act quickly. Shut off the water supply valve under the sink if you can, and place a bucket to catch drips while you decide on next steps.

Why Small Leaks Cause Big Damage

A slow drip might seem harmless, but it adds up. Even a few drops per minute can saturate the cabinet base and the subfloor beneath it. Wood absorbs moisture and swells, losing its strength and shape. Drywall in the surrounding wall can wick water upward, creating stains and weakening the material.

The damp environment also encourages mold growth. Mold can start growing within 24 to 48 hours on wet surfaces. Once it takes hold, it spreads quickly through the cabinet and into the wall cavity. That makes the cleanup more involved and may require removing and replacing affected materials. Catching a small leak early can save you from a much larger repair job.

What to Do Right Away

Start by turning off the water supply valve under the sink. This stops the flow and prevents further damage. Then dry the area as well as you can with towels. Remove any items stored under the sink so they don't absorb moisture. If you have a fan, aim it at the wet area to help it dry out.

Consider taking photos of the leak and any damage before you clean up too much. Those images can be useful for your insurance claim if you decide to file one. Policies vary, and your insurer decides what is covered. After you've dried the area, call a plumber to fix the specific leak, or contact local water damage pros if the damage has spread beyond the immediate area.

When to Call the Pros

If the leak has been going on for a while, or if you see signs of mold, warped wood, or water stains on the wall, professional help is usually wise. Local water damage pros can assess the extent of the moisture and recommend the right steps. They have tools to detect hidden moisture inside walls and under floors, which you can't always see with the naked eye.

Their work typically involves drying out the affected areas, removing damaged materials, and treating any mold growth. The exact process depends on how far the water spread and what materials got wet. If you live in Newark, keep your shutoff valve location written down so you can find it quickly in an emergency. Acting fast limits the scope of the repair.

  • Water stains spreading on walls or floors
  • Musty or moldy odor under the sink
  • Soft or spongy cabinet wood
  • Visible mold spots on any surface
  • Significant pooling of water
  • Leak that persists after tightening connections

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Frequently asked questions

How can I tell if the leak is from the supply line or the drain?

Dry all pipes and surfaces thoroughly, then place paper towels under each connection point. Run water through the faucet and watch for drips. Supply line leaks usually appear when the faucet is on, while drain leaks often show up when water flows down the drain. Check both areas separately to pinpoint the source.

Can I fix a small leak under the sink myself?

You can try tightening loose slip nuts or supply line connections with a wrench, but avoid over-tightening, which can crack fittings. If the leak persists after a gentle tightening, or if you see corrosion, the part likely needs replacement. For any leak you can't fix quickly, call a plumber to prevent further damage.

Will my insurance cover water damage from a sink leak?

Coverage depends on your specific policy and the cause of the leak. Sudden, accidental leaks are often covered, but gradual damage from a long-term drip may not be. Policies vary, and your insurer decides what is covered. Check your policy documents and document the damage with photos before filing a claim.

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