What Is the Black Soot in My Basement Toilet When It's Not Used for Weeks?

Significance

• Mold spores ride air currents throughout your home. If they land in a spot that is dark and wet, they will reproduce, eventually becoming visible mold growth. Severe mold growth can be dangerous to people with allergies or with weakened immune systems, such as infants, seniors or the ill.

Cleaning

• Black lines in toilets typically are mold growth. The simplest solution is to clean your toilet frequently to inhibit the mold growth. Bleach-containing bathroom cleaners often work best, but with enough scrubbing, less harsh cleaners should work as well.

Basements

• Basement bathrooms are especially prone to mold problems. Many basements have poor ventilation, meaning humidity is often high enough to promote mold growth. Also, you might not use your basement bathroom as frequently as others in your home, so you rarely turn the lights on and stagnant water remains in the toilet for a long time.

Warm Water

• Plumbers sometimes recommend feeding hot and cold water to a toilet rather than just cold. The warmer water keeps the toilet's exterior from getting too cool and developing condensation that promotes mold growth. This approach can backfire, however; the warmer water can promote mold growth within the toilet. Leaving the lid open might lessen the problem by allowing heat to escape and the above-water bowl surfaces to dry quickly after each use.

Dehumidifier

• Install a dehumidifier in your basement to solve the problem permanently. The dehumidifier will keep the air dry, making condensation and resulting mold growth less likely. To find the right dehumidifier for your basement, calculate its square footage and shop for a model that can handle the space.