How to Find a Water Leak Inside a Wall

Water leaks inside walls are a real headache for homeowners. They often go unnoticed until there’s visible damage like mould, peeling paint, or damp patches. Left unchecked, these leaks can lead to rotting timber, damaged plaster, and even affect the structure of the home.

Catching a leak early saves a lot of hassle. If there’s a strange smell, dampness that won’t go away, or you’ve noticed your water bill creeping up, there might be a hidden leak behind the wall. With a few simple checks and a bit of patience, it’s possible to figure out where the water is coming from and what to do about it before things get worse.

Why Wall Leaks Happen

Leaks inside walls can come from several sources. Understanding where the water might be coming from is the first step.

Leaking pipes: Over time, pipes can wear out, corrode, or develop pinhole cracks.
Poor waterproofing: If the waterproofing behind your bathroom or laundry wall has failed, water can escape.
Roof or gutter issues: Rainwater can travel through wall cavities if there’s damage above.
Blocked drains or overflowing sinks: Water might back up and seep into walls.
Faulty appliances: Washing machines or dishwashers can leak at the hose connections.

Sometimes, the leak might not be directly behind the wet patch you see. Water can travel along surfaces or down pipes before showing signs.

Signs of a Water Leak Inside the Wall

Here’s what to look for if you suspect there’s a leak hiding in your wall:

1. Damp or soft spots on the wall

Touch the wall with your hand. If it feels damp, spongy, or soft in places, that could mean water is building up behind it.

2. Mould or mildew smells

If there’s a musty smell in the room that doesn’t go away with cleaning, there’s a good chance there’s mould growing behind the wall. Mould thrives in damp, dark places.

3. Peeling paint or bubbling plaster

When water gets into your walls, it lifts the paint or causes the plaster to swell. You might see bubbling, flaking, or large patches peeling off.

4. Stains or discolouration

Look for yellow, brown, or dark patches on painted walls. These stains are caused by moisture building up behind the surface and soaking through.

5. High water bills

If your usage hasn’t changed but your water bill has gone up, you might have a hidden leak somewhere in the house.

6. Wet flooring or skirting boards

Check the skirting boards at the bottom of the wall. If they’re warped, swollen, or damp, the water could be running down from inside the wall.

Step-by-Step Guide to Finding a Water Leak Inside the Wall

Now that you know what to look for, here’s a step-by-step guide to help you pinpoint the leak.

Step 1: Shut Off All Water Fixtures

First, turn off every tap, shower, appliance, and anything that uses water. Don’t flush the toilet or run the dishwasher. You want the whole system to be still.

Step 2: Read the Water Meter

Go outside and check your water meter. Take note of the numbers. Wait for about 30 to 60 minutes (without using any water) and check again. If the numbers have gone up, there’s a leak somewhere in the plumbing system.

This confirms that water is flowing when it shouldn’t be.

Step 3: Check the Location of the Damp Area

Now go back inside and examine the wall where you suspect the leak is. Take note of:

Whether the wall backs onto a bathroom, kitchen, or laundry
If any water fixtures are located on the other side
If the wall is on a lower floor (which could point to a leak above)

Leaks usually appear near plumbing, so start with those areas first.

Step 4: Use a Moisture Meter (Optional)

A moisture meter can help you find wet spots in the wall without cutting it open. These tools aren’t too expensive and are available at most hardware shops.

Hold the device against the wall and take readings in different spots. The highest reading will be closest to the leak.

Step 5: Knock and Press Along the Wall

Use your knuckles or a small tool to gently knock along the surface. Listen for any hollow or soft-sounding spots.

Also, lightly press against the wall to feel for any weak or soggy sections. This can help you find the spot where the water is collecting.

Step 6: Look Above and Below

Water doesn’t always drip straight down. It might run along pipes or beams, so check the ceiling, corners, and even the floor nearby. If the stain or dampness has travelled, you’ll need to trace it back to the source.

Step 7: Inspect the Adjacent Rooms

If the wall backs onto another room, check that side too. Sometimes the damage is more visible on one side, or the leak spreads across rooms.

Don’t forget to check behind furniture or large appliances that might be hiding water damage.

Step 8: Use a Thermal Imaging Camera (Optional)

A thermal camera shows temperature differences in the wall. Damp spots are usually cooler than the dry ones.

This tool is often used by plumbers, but you can hire one or ask a professional to come out and scan your wall. It helps pinpoint the exact spot without guessing.

When to Cut Into the Wall

If you’ve found a section that is clearly wet and you feel confident, you can cut a small inspection hole in the plasterboard to look inside. Make sure you:

Turn off the power to that area (for safety)
Avoid cutting near power points or light switches
Use a small keyhole saw to cut gently

Once the wall is open, you can inspect the pipes, insulation, and framing. If you see corrosion, cracks, or dripping water, you’ve found the source.

If not, you might need to open a second section to follow the water path.

What to Do After Finding the Leak

Once the leak is located, the next steps depend on what’s causing it.

For leaking pipes:

You’ll likely need a licensed plumber to replace or repair the pipe. Don’t attempt to patch it yourself with tape or glue, as it usually won’t hold up. If the pipe has burst or split, here’s a guide on how to fix a burst water pipe to help you understand what needs to be done.

For roof or gutter leaks:

Call a roofing expert to check for broken tiles, blocked gutters, or flashing issues. Water can enter walls from the roof, especially after heavy rain.

For waterproofing failure:

If the leak is from a bathroom wall, you might need to redo the waterproofing membrane, which often requires removing tiles and redoing the whole section.

For faulty appliances:

Tighten or replace the hoses, check the seals, and monitor again after the fix. Keep an eye out for leaks returning.

How to Prevent Future Wall Leaks

Regularly check water bills for unexpected changes.
Inspect your home’s plumbing every few months, especially in older homes.
Keep gutters clean and roof tiles maintained.
Use proper sealants in wet areas like bathrooms and kitchens.
Hire qualified tradies for installations and repairs. A poor plumbing job can lead to big issues down the track.

Final Thoughts

Finding a water leak inside a wall takes patience, but it’s not impossible to do on your own. The key is to spot the early signs, take your time tracing the problem, and know when to call in a professional. Acting early can save you thousands in repairs and protect your home from serious damage.

If you’re unsure or if the leak keeps coming back, it’s always worth getting a licensed plumber in to have a look. A quick check now can save you a lot of stress later on.