Ever notice red or pink slime forming inside your toilet or on your shower walls? It’s a bacterium called Serratia marcescens, and it can grow in wet areas.

Chlorine in city water helps prevent it, but if you have an activated charcoal filter you’re removing the chlorine, according to the North Dakota State University Extension Service.

Water from a private well has no chlorine either. This bacterium has been known to cause pneumonia, wound infections and urinary tract infections in hospital settings, so it’s important to get rid of it.

Stains are easy to remove with a general-purpose cleaner containing chlorine bleach. You can also add 1/4 cup of bleach to your toilet tank, let it sit for 20 minutes, and then flush the toilet a few times to remove all the bleach. Don’t leave it in your tank—it can damage rubber valves and seals.