What Causes Black Mold to Grow in a Toilet Water Tank?

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A toilet tank can provide the moisture mold needs to grow.

The water in your toilet tank should be clear and free of debris or contaminants. If you see black mold growth in your toilet, you'll need to take steps to remove the mold and prevent it from returning. Black mold can create health problems for those living in the house, especially if they have immune system or respiratory problems.

Health Concerns

Black mold poses serious health risks to anyone who inhales the spores, which lead to symptoms similar to a common cold. If you or someone else in the house has asthma, the mold spores may trigger a severe asthmatic attack. Wear an N-95 respirator while cleaning up black mold to avoid exposure. Wear gloves when touching the mold growth inside the toilet tank. (Purchase an N-95 respirator at a home improvement center.)

Mold Growth Conditions

Mold needs certain conditions to thrive. Organic surfaces such as the tank's walls and hard water deposits help supply mold with a nutrient source. Mold also grows well in moist environments such as your toilet tank and the lid. If the air inside your house is warm, the water inside your toilet tank will heat up, which is also conducive to mold growth.

Removing the Mold

You must remove the mold completely from the inside of the toilet tank. Start by closing the water supply line. Locate the shutoff on the wall behind the toilet and twist the valve completely clockwise to close. Flush the toilet to drain most of the water out of the tank. Use an ammonia-free soap and stiff-bristle brush to remove the mold from all surfaces inside the tank.

Preventing Future Growth

After scrubbing, wet the inside of the toilet tank with a mixture of 1/4 cup of bleach and 1 gallon of water. Keep the surfaces wet with the mixture for a minimum of 15 minutes, disinfecting the surfaces so mold won't grow again. To keep the tank water cool, install toilet tank insulation, which provides a layer between the tank's walls and the air outside the toilet.


Steven Symes

Steven Symes has been writing for six years. His articles have appeared on a number of websites, including some regular columns. Symes has been writing professionally since 2005. He currently holds a Bachelor of Arts in English from Brigham Young University and is partway through an Master of Arts in English at Weber State University.