That Smell Under the Kitchen Sink: Slow Leaks, Soft Cabinet Floors and Mold

By John Calhoun, owner of Mold Remediation Gettysburg PA · Updated October 24, 2026

Give me a paper towel and a day, and I’ll tell you whether that smell under the kitchen sink is a leak. Empty the cabinet. Wipe everything dry. Lay a sheet of paper towel flat on the cabinet floor, right under the drain and the supply lines. Run the faucet hard for a minute, fill and drain the sink, and run the dishwasher if it’s on the same sink. Check the towel then, and again the next morning. A wet spot tells you where to look, and that’s most of the job.

Where kitchen leaks start

EPA WaterSense’s home maintenance advice is to look under sinks for leaks at pipe connections, puddling or water spots. The usual suspects:

• The drain trap and its slip nuts. They loosen over time, and they only leak when water’s going down the drain.
• Supply lines and shutoff valves. A slow weep at a compression fitting can run for months.
• The faucet base. Water from the counter runs down around the faucet and drips inside the cabinet.
• The dishwasher drain hose and the supply line under it. These run behind the cabinet side, where you can’t see them.
• The garbage disposal. Leaks from the body or the seals tend to show up only when it runs.
• The refrigerator ice maker line, if it runs behind the cabinets.
• Summer condensation on a cold-water line, which can drip like a leak with no leak at all.

Why the cabinet gets it worse than the pipes

Most sink cabinet floors are particleboard or plywood. Particleboard drinks water, swells at the edges and doesn’t go back. Water that gets past the cabinet floor goes into the toe kick space, under the cabinet and into the floor, and it can run along the back of the cabinets to the next one. That’s how a cabinet leak grows: from the cabinet floor into the base, the toe kick, the flooring and the wall cavity. Each step makes a small job bigger.

What gets cleaned and what gets replaced

Don’t paint over it or seal it. The EPA says not to paint or caulk moldy surfaces. If growth is past what you can clean in an afternoon, or the wall behind is wet, mold behind drywall explains what’s next.

When the water ends up downstairs

About 37% of Gettysburg borough homes sit in buildings with at least two units, by the Census Bureau’s latest count. In a building like that, a kitchen leak on the second floor often gets noticed first on somebody else’s ceiling. If that’s how you found out, start with whoever lives above, and look at mold in rowhouses and shared walls and the downtown Gettysburg page. For a leak you still can’t find, tracking down a hidden leak walks through it.

One thing to do today

Open the sink cabinet and look. Empty it, check the towel test above, and put a cheap water sensor on the cabinet floor when you put things back. EPA WaterSense notes those sensors can sit right under a sink’s drain pipe and sound an alarm when they get wet. The appliance leaks next door are in mold from a water heater or washer leak.

If the cabinet floor is soft or the smell won’t quit, call me, John Calhoun, at Mold Remediation Gettysburg PA. I’ll find where the water’s coming from before anybody replaces a cabinet. The mold services page explains how, and the overview of mold remediation in Gettysburg, PA covers the rest. More on Gettysburg’s housing mix is on the Gettysburg housing data page.