Leak Under Bathroom Floor – How to Locate

BY |

Have you detected a strange, musty odor in your bathroom? Water puddling on the bathroom floor? Mold forming? Or is your toilet shifting, or do you hear a hissing noise?

Hidden water leaks in the bathroom can lead to huge problems with the structural integrity of your bathroom and surrounding rooms. It can also affect your water bill, cause major damage and lead to huge plumbing repair costs.

How to Find a Bathroom Leak


Here are some signs you may have a toilet leak, damaged drainpipe, or some other plumbing issue that requires your immediate attention.

Musty Odor

If you notice a musty, earthy odor or other strange smells, it indicates that accumulating water has no way for it to escape or dry. The musty smell is a symptom and not the problem.

Water Puddling on the Floor

Another common cause for water on a bathroom floor is condensation outside the toilet’s tank, causing dripping on the floor. But this water accumulation can be a sign of a more serious problem and not a sign of a leaky toilet.


It is common for mold to gather in the corners of your shower because it is wet. But problems arise when mold becomes visible in parts of the bathroom that are usually dry, such as floors, ceilings, and non-shower walls. Mold growth in these areas is a sign that water is accumulating beneath the surface of the floor.

Damaged Flooring

A bathroom floor seldom suffers water damage unless there is a leak. So, if you notice the floor in your bathroom cracking, buckling, or staining for no apparent reason, hidden water is the reason. On the other hand, the water could be coming from broken pipes underneath the floor.

Moisture can make the bathroom floor feel spongy or soft. Also, it may cause floor tiles to become loose, allowing them to shift . Tiles may lose adhesion, enabling you to remove a piece of tile to expose the moisture or standing water beneath it. You will find a damp subfloor with severe rotting as well.

Shifting Toilet

A toilet can move because the mounting bolts that hold it in place no longer have anything to grab onto. The bolts do not go into the floor but secure to the toilet flange. But water escaping from under the toilet can indicate a more serious bathroom leak.

Structural Integrity Loss

Water accumulation can cause dark water stains along with severe structural damage. In addition, it can have damaging effects on floors, walls, and ceilings beyond the evident mold formation. A leak can cause the drywall to deform, causing it to bubble, warp, or deteriorate. This would be a labor-intensive and expensive repair as the drywall would need to be removed and replaced in addition to finding and fixing the leak. If the walls have a wallpaper covering, a moisture buildup behind it can cause it to fall off the wall.

Ceiling Stains

If you notice staining on the ceiling beneath the bathroom, it is one of the signs of water damage. Unfortunately, this is also troublesome and expensive to repair as patches of the ceiling may need to be replaced. In addition, if the water leak is not addressed immediately, it can cause the floor joists to become damaged and weakened.

Increase in Water Bills

A sign of a water leak will be apparent in your water bill. Monitor your account and water usage to see if they correlate. If your statement reveals more water consumption than you expect to see, it can be due to a bathroom leak. Once the leak has been repaired, your water bill should stabilize.

Ways to Prevent Bathroom Leaks

There are simple ways a homeowner can prevent bathroom leaks before they become a problem.

Ensure there are no spaces or gaps where water can enter through floors or walls. Damaged caulking or tile grout needs to be maintained to prevent water leakage.

In addition, the space between showers, tubs, and floors should be caulked, and make certain worn-out parts are replaced immediately to avoid water buildup. An exhaust fan will help heat and moisture escape, so mold is not as likely to form.

How Can You Find a Bathroom Leak

The primary cause of bathroom leaks is inadequate waterproofing before tiling. This can be especially true for older homes when waterproofing products were not as good as today. But it can be a problem for newer homes if the construction was inferior.

To find the source of drain, tile, sink, or toilet flange leaks, you need to determine which bathroom fixture is the source of the water escaping or stagnant water.

Turn on each fixture, one at a time, to check for drips or a wet spot to see if it becomes worse with anyone fixture.

Leaving the water on for several hours in the shower or bathtub can help determine if a leak exists in one of these fixtures. Understand that a hole as small as a pinprick can cause a massive leak.

Check the pipe between the valve and showerhead. Also, check the pipes between an upstairs bath and the lower ceiling. If you cut a hole in the ceiling below, it will enable you to inspect the pipes to see if they are leaking under the flooring.

After flushing the toilet, if water accumulates at the base, the flange may need replacement.

A loose, or broken toilet flange can cause a toilet to leak from the bottom when the seal under the toilet fails.

But, when a new wax gasket is installed between the toilet and the flange, creating a watertight seal should correct the problem.

If you find leaky pipes, contact a plumber immediately. Unless you are a plumber, allow the pros to fix these issues. They can inform you if it is necessary to lift off the tiles, waterproof the space, and replace them.

How Do You Detect a Leak Under The Floor

One of the usual sources of water puddles on the bathroom floor is a damaged and leaking pipe under the sink. Yet, there may also be a damaged pipe in one of the surrounding walls through which the water is leaking.

The most effective way to detect water leaks is by using professional sound detection equipment. With headphones and a microphone, a skilled technician can listen for running water as it flows through the pipes.

How Do Plumbers Find Water Leaks?

Plumbers use acoustic listening devices to detect pinpoint leaks. With sound technology, they can hear the sound of dripping and escaping water even through a layer of concrete.

Is A Water Leak Under the Bathroom Floor Covered By Insurance?

Yes — if the cause is an event that is covered by your homeowner’s insurance policy. Your insurer may be able to help pay to repair the water damage to your home.

However, if the cause is through homeowner negligence, the owner will need to absorb the cost of the repairs.

Water On The Bathroom Floor But No Leak

If you see no signs of leaks in the ceiling or around any water fixtures throughout the bathroom, it can be assumed there is a leak under the floor.

Inspect the floor as well as you can. If you notice a bulge in the flooring of your bathroom, you have found the source.

Can Water Come Up Through The Floor

A common cause for leaks coming up through the floor could be a ceiling crack or a crack in the home’s exterior. Both will permit water to enter.

In addition, when water seeps up through the floor, it could result from a poorly sealed foundation or cracks in the foundation floor.

Make Sure to Dry Out Your Home

When you have found and repaired any leaks in your bathroom, make sure there is air circulating, humidity is not too high, or the temperature too low.

Use floor fans or ceilings fans to help to begin the process of drying out the bathroom. If not too hot and humid outdoors, open windows will also help dry out the room. It will remove the water vapor and fuel the process of drying out the space.

Remove any objects that have been affected by the water leak. Items you wish to keep can be dried and saved by putting them in sunlight to speed up drying.

Do not allow wet items to remain in the home for an extended period as it becomes a breeding area for mold and mildew. As they can bloom within 24 to 36 hours, this is a crucial step.

Based on the amount of standing water that has resulted from the bathroom leak, you may need to use a wet vac to suck up the majority of the water.

However, do not use a regular vacuum, as they are not equipped to handle water removal and can be very dangerous if used for this purpose.

Leave a Comment