Hidden leaks

Musty Smell in the House? How to Tell If It Is a Hidden Leak

A damp, earthy smell that keeps coming back often means water is hiding somewhere. Here is how to track it down.

By the Arlington Leak Pros team · October 18, 2026

Moisture meter testing a shower wall for hidden water in an Arlington, TX home

A musty smell is often the first sign of a hidden water leak. Damp drywall, wet carpet pad and soaked wood give off an earthy, mildew-like odor, long before you see a stain. If the smell keeps coming back in one area, water is likely getting in somewhere. Call (817) 285-5426 for hidden leak detection in Arlington, 24/7.

Why does a hidden leak make a house smell musty?

When drywall, insulation, wood or carpet stay damp, mold and mildew begin to grow. They release the musty, earthy smell people notice. Hidden leaks keep these materials wet for days or weeks, which is why the smell lingers in one room even after cleaning.

Where do musty smells from leaks usually come from?

The most common sources are under kitchen and bathroom sinks, behind showers and tubs, around toilets, near the water heater and washing machine, under carpet near a slab leak, and in ceilings below upstairs bathrooms. Closets that share a wall with a bathroom are another frequent spot.

Under sinks
Behind showers and tubs
Around the toilet base
Near the water heater
Behind the washing machine
Carpet near a slab leak
Closets next to bathrooms
Ceilings under bathrooms

How can you check for a hidden leak yourself?

Follow your nose to the strongest spot. Look and feel for damp or soft drywall, stains, peeling paint, warped baseboards and damp carpet. Check under sinks with a flashlight. Then turn off all water and check the water meter. If it moves, a pressurized pipe is leaking somewhere.

Our water meter test guide walks through it step by step.

Could the smell be something other than a leak?

Yes. Musty smells can also come from high indoor humidity, an AC drain line that is clogged or leaking, a dry floor drain or P-trap, a dirty AC filter or coil, or a roof leak. If the smell gets worse after showers or near plumbing walls, a plumbing leak is more likely.

A sewer or rotten smell is different from a musty one. Sewer odors point to drain or sewer line problems. See our sewer camera guide.

Think you have a leak? A licensed Arlington technician answers 24/7.

Call Now (817) 285-5426

How do pros find the leak behind the smell?

A technician maps moisture with a moisture meter, scans walls, floors and ceilings with a thermal camera, and pressure tests the water lines to see if one is leaking. Acoustic gear can hear a pressurized leak inside a wall or under the slab. This finds the source without tearing out large areas.

Read more in how leak detection works and our guide to leaks in walls and ceilings.

Why should you act quickly?

The longer materials stay wet, the more damage builds up: rotting wood, ruined drywall and flooring, and spreading mold. Fast action also matters for insurance, since many policies do not cover damage from long-term leaks. Find the source, stop the water, then dry the area fully.

See our guide on what insurance usually covers for leaks.

How much does it cost to find a hidden leak?

Basic leak detection in Arlington usually costs about $150 to $400, and slab leak detection about $250 to $600. The price depends on how many areas need checking and how easy they are to reach. You get a clear price before any work begins.

See our full leak detection cost table.

Frequently asked questions

Can a hidden leak cause a musty smell without visible water?

Yes. Water can soak drywall, insulation or carpet pad from behind or below long before a stain shows. The smell is often the first clue.

Will an air freshener or dehumidifier fix the smell?

It may hide the smell for a while, but it will not stop the leak. If water keeps getting in, the smell and damage will come back.

Is a musty smell under the sink a leak?

Often, yes. Check for damp cabinet floors, drips at the supply lines and drain, and swelling in the wood. Even a slow drip can cause a strong smell.

Should I call a plumber or a mold company first?

Find and stop the water first. A leak detection plumber locates the source so it can be fixed. Then deal with drying and any mold so the problem does not return.