Tap water in the United States is a dire situation. Not just in rural areas or towns that occasionally pop up in the news, but in all 50 states. That’s because tap water contaminants are just about everywhere and can’t be adequately controlled by federal regulations alone.

Across the U.S., water is treated in large facilities where levels of 94 contaminants are regulated by the U.S. Environmental Protection Agency. If these requirements are met, the water is considered legal for drinking. But legal doesn’t mean safe. That’s because the regulations actually allow unhealthy levels of certain contaminants. And it doesn’t take much to reach these levels, sometimes only 1 drop in an Olympic-sized swimming pool.

Even worse, there are many contaminants known to cause cancer and other health concerns that aren’t regulated, even though they have been commonly found in U.S. tap water supplies. In some cases, even if water is legal when it leaves a treatment facility, it can become contaminated on its way through service pipes and into homes.

The threat these contaminants pose is real and you cannot rely on how your water tastes, smells, or looks to determine if it is safe to drink or not. These contaminants are dangerous at levels well below what any human can sense or detect. Click on a contaminant below to learn more about its prevalence, the dangers it poses to your health, and what you can do to reduce your exposure.