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How to Tell If Toilet is Leaking Underneath?

Leaking toilets may cause water damage and higher utility costs if ignored. On the other hand, a hidden toilet leak might be hard to find. A simple test may show “How to tell if the toilet is leaking underneath?”

To detect a toilet leak underneath, look for water pooling around the base, soft or damaged flooring, foul odors, and mold growth. Also, consider an unexplained increase in water bills or a constantly running toilet. Perform a dye test by adding food coloring to the tank and checking if it appears in the bowl without flushing.

This article will show you how to identify whether your toilet is leaking beneath and how to fix it.

how to know if toilet is leaking underneath

Indications That A Toilet Is Leaking Underneath

Some signs of a toilet leak underground are prevalent. These indications may indicate a leak. Underneath the toilet leak, signs are as follows.

Water pooling around the base

If you notice water pooling on the floor around the base of the toilet, it is a clear sign of a leak. Look for moisture.

Deteriorating flooring

A toilet leak underground might damage the flooring surrounding it. Look for floor softness, discoloration, or warping around the toilet.

Musty or unpleasant odor

Mold and mildew may develop in bathrooms due to leaks. An undetected leak may cause a lingering stench.

Elevated water bills

A sudden rise in your water bills without a clear explanation can indicate a hidden leak. If your water use has increased, check for a leak beneath the toilet.

Loose or deteriorated sealant near the base

Check the caulk seal within the ground of the toilet. It may leak if loose, broken, or degraded.

Toilet instability

A toilet leak weakens the flooring, making the toilet unstable or moving slightly. Sitting on a toilet that rocks or moves may indicate a leak.

Stains or water damage on the ceiling below

In high-rise structures, a toilet leak may end up in water stains or collapse on the ceiling of the room located below the bathroom. A toilet leak may cause ceiling discoloration or water stains.

Here is a video that demonstrates how to tell if the toilet is leaking underneath.


Leak Detection Beneath The Toilet

There are various ways to find a leak beneath your toilet. Common methods:

Visual inspection

Check the toilet foundation first. Look for floor water, dampness, or discoloration. Check the base caulk seal for damage. Water stains, moisture, or deteriorating caulk may indicate a leak.

Paper towel test

Leave dry paper towels around the toilet base for many hours. Check the paper towels for dampness after the time. Leaks beneath the toilet cause moist paper towels.

Water meter test

Turn off all household water sources. Check your water meter. Check the meter after a few hours without using water. Changing meter readings may indicate a water leak, especially one beneath the toilet.

Dye test

A dye may detect under-the-toilet leaks. Add a few drops of food coloring or a commercial dye tablet to the toilet tank. Check the toilet bowl water after waiting a while. Leaks beneath the toilet cause coloring in the bowl.

Listening for sounds

Sometimes, leaks can produce audible sounds. Hissing or leaking noises around the toilet base or nearby indicate a leak. These noises may suggest a leaking toilet connection or seal.

Professional inspection

If the measures above fail to locate the leak, call a plumber. Plumbers use cameras and leak detectors to find and diagnose toilet leaks.

How to Repair the Toilet Leak?

To avoid damage and water waste, fix a toilet leak immediately. Fixing a toilet leak involves the following steps:

Turn off the water supply

Before starting any repair or investigation, shut off the water supply to the toilet. Turn the shut-off valve clockwise to cease water flow. This stops water from leaking while you fix it.

Tighten loose connections

Check the bottom water supply line connectors and the tank-bowl connection. Wrench loose connections. Overtightening might harm.

Replace broken parts

If you find a broken fill valve or flapper, replace it. These components may cause toilet leaks or inefficiency. For proper replacement components, see the toilet’s handbook or call a plumber.

Repair or replace the wax ring seal

If the leak is coming from between the toilet base and the floor, the seal may be the problem. To fix this, remove the toilet, replace the wax ring seal, and fasten it. If you’re uncertain, consult the manufacturer or a specialist.

Seal the toilet flange or replace a damaged flange

A damaged or improperly sealed flange can cause leaks. Replace broken flanges. If the flange is intact but not sealed to the floor, a new sealant may prevent leaks.

Test for proper functioning

Once you’ve made the necessary repairs or replacements, turn on the water supply and flush the toilet. Flush and check for leaks. Check the tank water level and toilet flushing and refilling.

Seek professional assistance

If you’re unwilling to identify or resolve the leak, or if you’re uncomfortable doing the repairs yourself, it’s suggested to contact a professional plumber. They can identify and fix complicated leaks.

Diagnosing and Solving Tank-Bowl Leaks

Food coloring may test for a toilet tank bowl leak. This approach detects tank-to-bowl water leaks. Follow the steps below to detect tank-bowl leaks.

  • Start with a clean and dry toilet bowl:  Flush and let the toilet bowl dry before continuing. Ensure that the toilet bowl is free from any water or debris.
  • Add food coloring to the toilet tank: Choose a bright color of food coloring, such as red or blue. It will be easily visible in the toilet bowl. Add food coloring to the tank water. Don’t flush during this process.
  • Wait and observe: Leave colored water in the tank for 20–30 minutes.
  • Analyze the results: A tank-bowl leak is indicated by colored bowl water. This test suggests a leak, but the location and reason may need more examination.

How to Solve the Tank-Bowl Leak?

Fixing a tank-to-bowl leak detected through color testing involves these steps:

  1. Flush and hold the handle to drain the tank.
  2. Unscrew the bottom tank bolt nuts using a tool or pliers.
  3. Lift the tank of the bowl and inspect the gasket or washers between them. Replace them if they’re worn, cracked, or damaged.
  4. Get a new gasket or washer made for your toilet model. Swap out old ones, seal the tank, and bowl properly.
  5. Put the tank on the bowl, align the bolt holes, and tighten. Tighten the tank bolt nuts, but don’t overtighten them, or the tank may shatter.
  6. Turn the valve counterclockwise to restore water. Let the tank fill.

Fill the tank, and watch for leaks between the tank and the bowl. No leaks, problem solved.

If the leak remains after changing the gasket or washers, it’s best to contact a professional plumber who can further diagnose and address the issue.

Toilet Leak Prevention And Maintenance

maintenance toilet and prevention toilet leak

Preventing toilet leaks may preserve your bathroom. Toilet leak prevention involves these steps:

Regular toilet inspections

Look for leaks, cracks, and wear. Check the tank, bowl, and surroundings. Early identification prevents leakage.

Water line inspection

Check the toilet tank water supply line regularly. Check that the connection is safe and undamaged. Replace a cracked or leaking supply line.

Maintain effective sealing

Make sure that the wax ring seal between the toilet base and the floor is intact and in excellent shape. Replace the wax ring seal immediately if it leaks or degrades. To keep the toilet waterproof, check and repair the caulk seal around the base.

Avoid flushing improper materials

Teach family members not to flush sanitary products, wipes, paper towels, or extra toilet paper, which may clog the toilet. Flushing just human waste and toilet paper prevents obstructions and overflows that might cause leaks.

Keep track of water pressure

High water pressure can strain the toilet’s components and potentially lead to leaks. For safe water pressure, place a pressure regulator on your water supply line.

Prevent condensation

Toilet tank condensation may cause leaks. A tank liner or toilet tank condensation kit reduces condensation and water damage.

Regular maintenance

Clean the toilet tank, bowl, flushing mechanism, and flapper valve. Regular maintenance might catch small faults before they become major leaks.

Fix running toilets

Fix a running toilet right away. Running toilets waste water and strain toilet components, which may cause leaks. To repair, replace the flapper or fill valve.


Preventing toilet leaks is essential for a water-efficient bathroom. By monitoring for leaks, inspecting regularly, and taking preventative actions, you may avoid water damage, waste, and expensive repairs.

Maintain the seals, check the water pressure, and teach your family members proper flushing. Preventive maintenance keeps your toilet system leak-free and extends its lifespan. Proactive actions will provide you peace of mind and improve the environment. On the other hand, if leaks happen, take the repair measure as soon as possible.