How to Tell if a Toilet is Leaking Underneath

Tracking down a hard-to-discover leak underneath your toilet can be a hassle. You may think of it as a spill and dry it with a dry cloth, only to find your toilet floor flooded after a few hours. In the long run, this can lead to excruciating water bills and other threats, such as harmful mold development in your bathroom. Therefore, it would be best to attend to a leaking toilet as soon as possible.

A toilet leaking underneath has a musty/sewer smell, wet/damaged floor, mold or mildew, and a swaying toilet seat from holes in porcelain potties, loose bolts, worn-out wax rings, leaking pipes, and condensation. To fix it, tighten loose bolts, replace wax rings, limit condensation, and seal leaks.

Luckily, this discussion will show you how to tell if your toilet is leaking underneath, alongside other helpful information you may need. Read on!

What are the Signs of a Toilet Leaking Underneath?

Most probably, you may notice your toilet is leaking underneath due to a high water bill. However, you can also tell from other signs, which include:

1. Musty Smell

A toilet leaking underneath always leaves a musty smell, even after a thorough cleaning. You may attempt to clean your bathroom with a brush and powerful detergents and end up smelling a horrible smell afterward. This is a clear sign that your toilet is leaking underneath.

You may also notice a sewer gas smell as the gasses from the drain pipe leak into the bathroom.

2. Wet/Flooded Floor

If your toilet is leaking at its base, you’ll most probably identify a wet floor if your bathroom floor lacks a floor water trap. You may dry your floor using a dry cloth but find it wet after using your toilet several times. If this happens, you should try flushing your toilet and inspect its base to identify the primary source of the leak.

3. Mildew or Mold

Typically, mold or mildew thrives in a dark and moist area. Leaking pipes within your bathroom floor are a perfect place for mold-breeding. If you identify mold in your bathroom or experience allergic reactions such as wheezy breath or irritated eyes, it’s most possible your toilet is leaking underneath. 

Keep in mind that it’s usual for some minor mildew to grow within an area where water accumulates, such as at the corner of your shower. However, if it develops on your non-shower walls or corners of your bathroom, it’s a clear sign of leaking within those areas.

4. Damaged Flooring

If your bathroom floor is cracking, buckling, or beginning to stain and you don’t have a running faucet, odds are that your toilet is leaking at its base. The water could be running from a pipe underneath the floor, or it could have moved from one area to another. 

You might feel your bathroom floor spongy or soft. Also, you might pick up some tile peel-offs on the floor. Nonetheless, your toilet is leaking underneath and needs to be fixed to prevent further damage.

5. Swaying Toilet Seat

A toilet seat should always be stable and firm. If you start feeling it like a rocking horse, the wax ring that acts as a water seal between its base and the drain pipe is worn or the floor bolts are loose. 

You may not identify wastewater on the floor or detect a foul smell in your bathroom. However, you may notice them after some time.

What Causes a Toilet to Leak Underneath?

Here are the leading causes why your toilet is leaking underneath:

1. Holes in a Porcelain Potty

Most toilets are modeled in porcelain. Although this material looks nice and clean, it is imperfect such that you may have some holes in your toilet basin. These holes will cause your toilet to leak underneath every time it is flushed.

2. Loose Bolts

Every toilet should be firmly fixed on the floor with two bolts. You may not easily see these bolts since they have a cap that covers them. However, you can carefully remove the caps to identify these bolts. 

If these bolts are loose, the toilet seat and the floor seal are ineffective. This will make water escape after flushing due to high pressure.

3. Worn Out Wax Ring

The wax ring is a seal between the toilet underneath and the connecting outflow pipe. This ring can quickly wear out due to loose bolts or powerful toilet chemicals, making your toilet leak underneath.

4. Leaking Pipes

Any surface with pipes can easily leak. To identify whether your toilet pipe is leaking, you need to use a dry cloth to dry the toilet base surface. After you acquire a dry surface, flush your toilet and watch for any signs of leakage.

You can also use your hand to feel along the surface of the pipe while paying much attention to the joint for any sign of leaking water.

5. Condensation

Other times, condensation within the toilet may act as a sign of a toilet leaking underneath. 

Typically, as cold water gets into the toilet tank, it changes the temperature of the surface of the tank’s exterior. If your bathroom is warm or there’s warm air in your house, water may begin to condense on the outer area of the toilet tank. This accumulation of condensed water may start to drop underneath the toilet surface. 

If this happens, you can at least get relieved since your toilet is not leaking from underneath. 

What to Do if a Toilet is Leaking Underneath

It is always quite costly to call for a profession whenever a problem arises in your home. You can attempt fixing your toilet if you notice it leaking from underneath. The following are some ways to go about it:

Tighten Loose Toilet Bolts

Remove the dome-like caps on the toilet base if you notice loose toilet bolts. To detach these caps, squeeze them, use a screwdriver, or use a nail file to loosen them. 

If your toilet sways, then these bolts need to be tightened. Use pliers to grab the nuts, and turn them clockwise to tighten them. 

You should be gentle when tightening these nuts. Overtightening them can crack your porcelain base, making your toilet unusable. 

After completing this process, try to wiggle the toilet sideways. If you’ve tightened the bolts sufficiently, the toilet seat will not move. Alternatively, you can replace the plastic bolt caps.

Replace a Worn Out Wax Ring

You can easily replace worn out toilet wax ring using the following steps:

  1. Turn Off the Water: Turn off the water supply line below the toilet water tank then flush the toilet and remove the water supply line from the toilet.
  2. Drain the Toilet: Use a dry towel to soak up water at the base of your toilet bowl. 
  3. Remove the Floor Bolts: Remove the plastic bolt caps and use pliers to unfasten the floor bolts.
  4. Remove the Toilet Seat: Shake the toilet slightly to detach it from the floor surface. Then, raise it upwards to remove it. Put the toilet seat aside.
  5. Scrape the Wax Ring: Remove all the old wax rings at the toilet’s base. You can use a putty knife to erode all the wax remains from the floor toilet flange.
  6. Fix the New Ring: If you are replacing it with a wax ring, put it at the toilet’s base, positioning it at the center of the drain hole. If you use a silicone ring, install it on top of the floor closet flange.
  7. Reset the Toilet: Reset the toilet back to its position using the floor bolts. Position the toilet right on top of the bolts. Insert the floor nuts and tighten them using pliers. Later, reattach the water supply line and turn on the water to fill the tank before flushing the toilet.

Different toilet designs might have different ways to seal the space between the toilet and the drain pipe but most use wax rings which can be replaced with these steps.

Seal/Replace Leaking Pipes

Suppose leaking pipes are the cause of your toilet leaking underneath. You can quickly seal them using a pipe joint compound to prevent leaking. If this doesn’t work, you can consider replacing the pipe with cheap, affordable pipes.

Limit Condensation in Your Bathroom

If condensation is the leading cause of the wet floor in your bathroom, you can easily control it using a few simple hacks. For instance, you can install a bathroom exhaust fan to equalize the temperature in your bathroom. 

Also, you can install a toilet tank drip tray between the toilet tank and bowl for collecting condensed water. This will prevent this water from dripping on the bathroom floor.


It can be hard to tell if your toilet is leaking underneath. However, you can use our simple hacks to discover signs of a toilet leaking from underneath and identify the possible causes. 

You can also use our simple methods to fix a toilet leaking from underneath to get out of this problem. Thankfully, you will leave your toilet free from underneath leaks and live a hassle-free lifestyle.

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