Cancer-causing contaminants may be in your drinking water, according to a new study published in the journal Heliyon.

Scientists at the Environmental Working Group (EWG) analyzed pollutants in tap water from 2010 to 2017. They found 22 carcinogenic contaminants — including arsenic, disinfection byproducts, and radioactive contaminants, such as uranium and radium — in drinking water nationwide, which researchers estimate could, over the course of an average lifetime (about 70 years), lead to 100,000 cases of cancer.

The analysis found that water systems with the highest risk tend to be small groundwater systems. “These systems typically lack the resources, funding, and infrastructure to effectively manage water contamination, and arsenic — a potent carcinogen — is typically found in groundwater,” says Evans.

But larger water systems aren’t necessarily safer. Evans says they also show “consistently elevated risk” because they contain disinfection byproducts, which are a result of required disinfection. “There are contaminants in drinking water that pose health risks other than cancer,” she says. So the disinfection of water is extremely important! And immediate action.