What Causes Black Stains In The Toilet Bowl?

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Last Updated on November 12, 2022 by acechapman

It is often quite obvious why certain colors appear in our toilets, depending on what we have done in the last few days – yellow and brown are common examples. When you see a color such as black, what happens? What causes black stains in the toilet bowl?

What causes black stains on toilet bowls?

There are a few possible causes of black stains on the toilet bowl. The main culprits are hard water, bacteria, and mildew.

Hard Water

Mineral deposits can build up from hard water usage, especially in areas with heavy flows like your toilet. You can see the black, brown, red, or rust waterlines in the toilet bowl where there is the most flow.


It is usually pink in color, but it can become black if there are a lot of bacteria. This bacteria can be found in toilet bowls and can spread via human waste.

Mold and Mildew

Your toilet could develop mildew if it is not used often and the water is stagnant for a long time. This could lead to black stains on the toilet bowl. Mildew needs both an organic surface and a moist environment in order to thrive.

These conditions can be satisfied by hard water deposits under the rim of your toilet bowl.

Although the bacteria and hard water may not look very appealing, they are relatively harmless. Black mold can pose a threat to your health. It is important to get rid of black mold as soon as you can.

black stains in toilet bowl

How do you remove black stains from a toilet?

If you have stubborn black stains, you can either choose one or both of these options. All of them require the same steps: ventilate the area as much as possible and wear your protective gear.

You will need the following tools and materials:

  • Gloves
  • A breathing mask
  • Eye protection or face shield
  • Vinegar
  • Use Magic Eraser, a scrub brush, or a toilet brush
  • Bleach
  • Spray bottle
  • Borax OR baking soda


Flush and drain the toilet.

Clear views of black spots and water lines are important.

Sprinkle baking soda or Borax on the surface, and then spray vinegar

Concentrate on getting the baking soda and Borax onto the waterline, as well as any black spots. Don’t forget to reach below the rim! Spray the vinegar on top of the baking soda. Once you have the vinegar removed, add about a cup of the vinegar to the tank along with the water. This will also help to clean any other growth in the tank.


Allow the solution to sit in the bowl for approximately 1-1.5 hours. Use a scrub brush, a toilet brush, or Magic Eraser to scrub the bowl. You can also clean the toilet tank with a scrub brush or Magic Eraser, but please be mindful of all parts. You may have to replace parts or damage them if you do.

Flush the Toilet

Allow the bowl to sit in the solution for 15 minutes. Then, flush.

Bleach OR Hydrogen Peroxide

Toss in bleach

You should add about 1 cup of bleach or hydrogen peroxide to your toilet bowl. Make sure you pour it in the toilet water as well as around the bowl. Don’t forget the underside! You can also add approximately 1 cup of bleach or hydrogen peroxide to your toilet tank.


Use your scrubbing tools to scrub the bowl. You can also clean the tank, but be careful! ).

Let it sit

Allow it to sit for at most 15 minutes so that the hydrogen peroxide or bleach can kill any bacteria.


You can continue to flush the toilet a few times until all of the cleaning solutions are gone.

black stains in toilet bowl

What Is Wrong With Your Water?

The water is probably fine. However, it is possible that the black stains are caused by hard water buildup. This is normal and generally harmless.

There is always a possibility that the water supply is not working properly. You should check with the person responsible for the water supply in your region if you suspect this to be the case. They might already be aware of the problem and have solutions.

Why is there black residue in the toilet after flushing?

After flushing, you may notice blackened water. This could indicate that mold has grown in your water supply pipes.

Pipes can be rusty or leaking, making them a perfect breeding ground for mold. Mold could be coming in with water from your pipes leading to your toilet.

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