What Causes Water Damage Under a Kitchen Sink?
Last updated October 31, 2026
The short answer
Leaky Supply Lines
The flexible hoses that carry water to the faucet are a common source of trouble. These lines can develop pinhole leaks, crack at the connections, or loosen from vibration. Even a slow drip can soak the cabinet floor and the base of the sink over weeks.
Signs include water stains on the cabinet bottom, a damp smell, or small puddles that keep coming back. If you see any of these, turn off the shutoff valves and inspect the connections. Tightening a nut may fix it, but a cracked hose needs replacing.
Faulty Sink Rim Seal
The seal between the sink and the countertop can break down, especially if the sink was installed with old caulk or putty. Water from washing dishes can then seep underneath the rim and run down the sides of the cabinet. Over time, this can rot the cabinet wood and lead to mold.
Check for gaps or dark stains around the sink edge. If water beads up on the counter and runs toward the sink, the seal may be failing. Resealing the rim with fresh silicone caulk is a straightforward fix, but if the cabinet is already swollen, the damage may need professional attention.
- Look for dark streaks or water rings under the sink
- Feel the cabinet bottom for soft or spongy wood
- Check the area around the drain flange for dampness
- Run water and watch for drips under the sink
- Notice a musty odor that worsens after using the sink
Drain Pipe Issues
The drain pipe under the sink carries wastewater to the wall. The slip joints where pipe sections connect can loosen, and the rubber gaskets inside can dry out or crack. A leak here often appears as water pooling on the cabinet floor or dripping from the pipe itself.
Also, a clogged drain can cause water to back up and overflow the sink, soaking the cabinet. If the drain pipe is metal, corrosion can create small holes. Run water and watch the pipe joints for a few minutes to spot any seeping.
Loose or Corroded Fittings
The metal nuts and compression fittings that hold the supply lines and drain together can loosen over time, especially if the sink is used heavily. Corrosion on these fittings can also weaken them, causing slow leaks that are hard to see until the damage is done.
Tightening fittings may help, but if they are corroded, replacement is safer. If you live in Columbus, keep the location of your shutoff valves written down so you can stop the water quickly in an emergency. Regular checks under the sink can catch these problems early.
What You Can Do Now
Start by wiping under the sink dry and placing a clean paper towel on the cabinet floor. After a day, check the towel for dampness. This simple test can reveal a slow leak. Also, feel the pipes and fittings for any moisture, and look for water stains on the wood.
If you find signs of water damage, act quickly to dry the area and fix the leak. For extensive damage, such as swollen cabinetry or mold, the pros can help with inspection and cleanup. They can also handle overflow cleanup if the sink has flooded.
Bullets of common warning signs:
- Puddles or dampness on the cabinet floor
- Water stains or dark spots on wood or drywall
- Musty or earthy smell under the sink
- Soft or crumbling wood around the sink base
- Visible drips from pipe joints or valves
- Peeling paint or warped cabinet panels
Need help right now?
Call (614) 412-4391 any time, day or night, and describe what happened.
Call Now (614) 412-4391Frequently asked questions
How can I tell if the leak is from the supply line or the drain?
Run the sink water and open the cabinet. If the leak appears only while water runs, it is likely the drain. If it leaks even with the water off, the supply line or a valve is the source. Dry everything first, then watch closely.
What should I do if I find mold under my kitchen sink?
Mold can grow where moisture collects. For small patches, clean with a mild detergent and dry thoroughly. For larger areas or if you feel unwell, see a doctor. A mold professional can assess the extent and recommend removal.
Can I fix the leak myself, or should I call a plumber?
Tightening a loose nut or replacing a worn supply line is often a DIY job. But if the leak is from a corroded pipe or the damage has reached the cabinet, a plumber can handle the repair. For water damage cleanup, the pros can help.
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