Water Leak in a Wall or Ceiling? Signs, Causes and Next Steps

A leak inside a wall or ceiling can drip for weeks before you see it. The first signs are usually a stain, bubbling paint, soft drywall or a musty smell. The source is often a shower valve, a supply line, a drain or the water heater. If you see these signs, call our wall and ceiling leak team at (817) 285-5426, 24/7.

What are the signs of a leak in a wall?

The most common signs of a leak in a wall are water stains, peeling or bubbling paint, soft or swollen drywall, a musty smell, warped baseboards, and mold spots. A dripping sound inside the wall, or a damp spot on the other side of a shower wall, are strong clues too.

• Brown or yellow stains
• Bubbling or peeling paint
• Soft or swollen drywall
• Musty or damp smell
• Warped baseboards or trim
• Mold or mildew spots
• Dripping sound in the wall
• Loose tile or bad grout

What causes leaks inside walls and ceilings?

Most hidden wall and ceiling leaks come from five sources: shower and tub valves, cracked supply lines, leaking drain pipes, worn shower pans or grout, and a failing water heater or its lines. In two-story homes, an upstairs bathroom is the most common cause of a ceiling stain below.

Some ceiling stains come from roof or AC condensate leaks, not plumbing. A stain that only grows after rain points to the roof. A stain that grows after someone showers or runs a sink points to plumbing.

How can you tell if it is a supply line or a drain?

Check the water meter with every tap off. If the meter moves, a pressurized supply line is leaking, and it leaks all the time. If the meter is still and the stain grows only after showers, flushes or sink use, the leak is likely in a drain, shower pan or grout.

Supply line leaks are more urgent because they never stop. See our water meter test for step-by-step help.

How do pros find a leak behind a wall without tearing it out?

Technicians use a moisture meter to map how far the water has spread, a thermal camera to spot wet or warm areas behind the surface, and acoustic gear to hear a pressurized leak. Pressure tests confirm which line is leaking. This pinpoints the source, so only a small access hole is cut.

Learn more about each tool in how leak detection works.

What should you do right away?

If water is dripping or the ceiling is sagging, shut off the main water valve and turn off power to that area. Put a bucket under drips. If the ceiling bulges, a small hole at the lowest point can drain it safely into a bucket. Take photos for insurance, then call for leak detection.

1. Shut off water at the main valve.
2. Cut power to wet lights, outlets or fans.
3. Catch drips and move furniture and rugs.
4. Take photos of stains and damage for insurance.
5. Call a licensed plumber to find the source.

Is a wall leak an emergency?

A sagging ceiling, water near electrical outlets, or a leak you cannot stop are emergencies. Call right away. A small, slow stain is less urgent but should still be checked within a few days, because hidden moisture can rot wood framing and grow mold inside the wall.

For the full emergency list, see what to do during a leak.

How much does it cost to find a leak in a wall?

Basic leak detection in Arlington usually costs about $150 to $400. The price depends on how many walls or fixtures need to be checked and how easy they are to reach. The repair and drywall patch are priced separately, and you get the price before any work begins.

See our full leak detection cost table. If the stain is on a ground floor near the slab, it could also be a slab leak.