What Are the Causes of Mold in a Toilet Bowl?

If you have hard water, as many homes do, mineral deposits such as magnesium, calcium and lime may build up in your toilet bowl. Such deposits can give mold and a mildew a surface to cling to and colonize on if the bowl is grimy. Because of this, it's important to not only keep your toilet bowl clean but to also remove any mineral buildups. Most toilet bowl mold isn't the toxic black mold -- magnesium spots can be black -- so you can remove it using basic household products.

White toilet bowl in a bathroom
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A clean toilet is free of any mold or mildew.

Why Mold Grows in Toilets

Mold thrives in dark, moist environments, so toilet bowls are prime targets. If your toilet is dirty, the buildup of dirt and grime will also feed the mold, allowing it to grow quickly. Scaly mineral deposits inside the bowl also contribute to mold growth as they give it a surface to attach to and grow upon. Also, a lack of adequate air flow inside a bathroom can also encourage mold to form and multiply.

Removing Mold With Oxygen Bleach

One way to remove toilet bowl mold is with oxygen bleach; avoid using chlorine bleach, which kills bacteria needed for septic systems. First, turn on your bathroom exhaust fan or open a window to provide ventilation. Flush the tank to allow clean, fresh water into the bowl and then pour 1 cup of bleach into the tank and 1 cup of bleach into the bowl. Use a toilet brush to distribute the bleach all over the inside of the bowl, making sure to get under the rim as well. Close the toilet lid and allow the bleach to sit for an hour before scrubbing the mold away with the bowl brush. Add another cup of bleach to the tank and flush one more time to wash away the mold. If your toilet is prone to mold growth, add 1 cup of bleach to the tank every week for maintenance.

Removing Mold with Vinegar

Another way of removing mold from your toilet bowl is with vinegar. Pour 1 cup of distilled white vinegar in the toilet bowl and 1 cup in the tank. Sprinkle baking soda all around the toilet bowl and under the rim. Close the toilet lid and allow the vinegar and baking soda mixture to sit in the bowl for one hour. Next, scrub the mold away using an abrasive toilet brush. Close the lid and allow the mixture to rest another 15 minutes before flushing the toilet. Again, you can add 1 cup of vinegar to the tank every week as maintenance.

Preventing Future Toilet Mold

The key to keeping your toilet bowl mold-free is cleaning it regularly, especially if you have hard water. In addition to keeping your toilet bowl clean, remove any mineral buildup as soon as possible with an abrasive cleaner or product, such as baking soda or steel wool. The longer grime or mineral stains sit in a toilet bowl, the higher the chances for mold growth. Also, install an exhaust fan in your bathroom or open a window a crack during a shower to reduce moisture and encourage good air flow.