How To Tell When A Toilet Is Leaking Underneath [Must Read!]

Usually, you can identify toilet leaks easily enough by the tell-tale dripping noise and falling water, but if your toilet is leaking underneath, then it’s all too easy to miss the problem until it is too late.

Not fixing a leaking toilet can cause problems down the line such as damage to your floors, pipes, and even the rooms below your toilet.

So how can you say that your toilet is leaking underneath if you can’t actually see the source of the water? (Link)

The most obvious sign is dampness or wet patches around the base of the toilet. Other common signs are foul odors, leaking noises, and water stains on the ceiling of any rooms downstairs from the toilet. By paying attention to the environment around your toilet, you can identify the effects of a leak.

Keep reading for more details on identifying leaks underneath your toilet compared to other common plumbing problems as well as common causes for such leaks.

What Are The Signs That Your Toilet Is Leaking Underneath?

You can’t exactly get underneath your toilet and check for running water the way you could if it’s leaking from the tank or the bowl.

However, there are a few tell-tale signs that you’ve got a leaky toilet on your hands even if you can’t physically see the source of the leak.

Here are some of the most common ones:

  • Damp, spongy, or mildew patches on the floor around the toilet.
  • A smell of urine or sewage.
  • Dripping noises without a visible leak.
  • Damp spots or damage to downstairs rooms.

Let’s take a look at all of these signs in more detail so you know how to identify this common problem.

Can A Leaky Toilet Cause Changes To A Floor?

The first place that you’ll see signs of a toilet leaking underneath is the floor around the base of your toilet, which makes sense because it is the closest to the site of the leak.

The most common sign of a leaking toilet is a wet or damp floor around the base. If you frequently find puddles around the base of your toilet and you know you didn’t spill anything or the bowl didn’t overflow, then it might be time to call in a plumber to look underneath your toilet.

Sometimes, signs of wetness around your toilet bowl are not as obvious as visible puddles of water.

If you’re unlucky, the water will leak underneath your flooring. Even if the leak isn’t visible to the naked eye, you can still see signs of water pooling.

For example, if the texture of the floor changes and suddenly becomes spongy, that is a sign that water is pooling underneath.

If you’re really unlucky, water is not the only thing that will show up around the base of your toilet.

If you clean your bathroom regularly but still notice dirt, mold, and mildew popping up, particularly around the base of your toilet, that could be a sign that you have a leak you don’t know about yet.

Why Are There Strange Odors That Linger Around The Toilet?

Besides visual changes and damage to your flooring, you can also detect an invisible leak thanks to your sense of smell. (Link)

We already mentioned mold and mildew spores appearing around the base of your toilet, but even if you don’t see any spores and just smell a damp, moldy smell, that could be a sign of an invisible leak. A more direct, unpleasant smell that signals a leaky toilet is the smell of sewage gas or urine.

When your toilet leaks, unfortunately, it’s not just plain water that gets released underneath your floorboards and who knows where else.

Your toilet could also be leaking gasses and waste, which is why it is imperative that you fix leaks immediately. If you notice consistent foul odors, call a plumber right away.

Why Do I Hear Dripping Noises Around The Toilet Area?

A less common but still tell-tale sign of a toilet leaking underneath is the consistent sound of dripping water. If you’re hearing dripping noises around your toilet but can’t visibly identify the source of the leak, then it’s probably happening somewhere you can’t see, such as underneath the toilet.

Before you go tearing up your toilet looking for the source of the mysterious dripping sound, make sure that you’re not missing a leak elsewhere. (Link)

For example, the food coloring test can help you tell if there is a leak in your tank. Put a few drops of food coloring in your toilet tank then don’t flush the water for several minutes. If the water in your bowl changes color, that means you’ve identified the source of the leak.

Sometimes, leaks from the tank and the bowl are not immediately visible, so it pays to rule out all those other potential sources before paying a plumber to rip up your toilet.

Can A Leaky Toilet Cause Water Damage To Other Rooms?

In really bad cases of toilets leaking underneath, the water could seep through your floors and damage the areas below. Check out the ceiling in the room or basement directly below your bathroom.

Do you see water stains or damp patches? That is a sign that your toilet is leaking underneath and that the problem is pretty severe.

Even if you don’t see any water damage on the ceiling of the room below, check again for stains and watermarks on the floor around your toilet bowl.

Sometimes, there won’t be visible pools of water, but you’ll still find stains. That’s usually a sign that the leak has been going on for some time.

What Causes A Toilet To Leak From Underneath?

There are a few different causes of a leaking toilet underneath.

The most common are loose bolts or washers, including the bolts that hold your toilet to the floor. Luckily, loosened bolts are an easy enough fix. Just remove the plastic covers, tighten the bolts, and replace the covers (be careful not to tighten the bolts too much, which is a common error people make when they want to be sure they’re plugging the source of the leak. That could crack the porcelain base of the toilet).

If your bolts are already tightened, then another possible cause of your leaky toilet could be your wax ring seal.

The wax ring goes around the connection between your toilet and the drainpipe. If the seal loosened, which is common as it gets older and dirtier, then your toilet will start to leak water and waste matter.

You can replace a wax ring seal yourself but it’s a bit complicated as you have to remove the toilet and turn off the water supply, so it’s best to call a professional.

If neither of these possible causes turns out to be the root of your problem, then double-check to ensure that the toilet is actually leaking from underneath.

If you notice a wet patch on the floor, it’s possible that the toilet is leaking from above, but you just didn’t notice the leak. Run your hand along the tank and the base of the toilet. If you notice wet spots, there’s a leak further up that you didn’t notice.

If you’re still having trouble identifying the source of the leak or don’t know how to fix it immediately, call a plumber.

What Should You Do If Your Toilet Is Leaking Underneath?

Once you figure out that your toilet is leaking underneath, you need to address the problem immediately.

Leaks can cause serious problems in the form of structural damage to your flooring and even the ceilings underneath your bathroom.

Even if the leak is not so bad, it can still make going into your bathroom an unpleasant experience thanks to wet patches and foul odors.

The best course of action, particularly if you’re not very confident in your DIY skills, is to call a professional plumber.

When so much damage is at stake, you don’t want to risk making matters worse as you try to “fix” it.

Frequently Asked Questions

Here are some of the most common questions people ask about toilets leaking underneath:

Is A Leaking Toilet An Emergency?

Yes, a leaking toilet is an emergency. You should immediately address this issue before the leak spreads and causes mildew or other damage to your flooring.

Can A Toilet Leak Under the Floors?

Yes, a toilet can leak under the bathroom floor. Usually, this happens when the toilet is not secured properly to the floor, for example, if the bolts aren’t tightened enough.

Even if you can’t see visible puddles, that doesn’t mean your toilet isn’t leaking.

The Final Word On Toilets Leaking Underneath

A toilet leaking underneath is a serious problem, particularly because it’s not always noticeable if you don’t know what signs to look out for.

The most common signs are damp or spongy spots on the floor around the base of your toilet, water stains on the floor or the ceiling downstairs, foul odors, and leaking noises without a source.

If you suspect that your toilet is leaking underneath, call a plumber immediately because you don’t want the damage to get out of hand.

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