CN) – Most Americans think of their drinking water is safe, but a new cumulative assessment of risks from 22 carcinogenic contaminants found in the nation’s water supply found chemical pollutants could be responsible for more than 100,000 cancer cases.

Scientists from Environmental Working Group used a new analytical framework to calculate the combined health impacts of carcinogens in 48,363 community water systems in the United States.

The U.S. Environmental Protection Agency identifies contaminants for regulation to protect public health, setting legal limits on over 90 contaminants in drinking water. EPA rules also set water-testing schedules and methods that water systems must follow, as required by the Safe Drinking Water Act.

But EPA regulations may not be enough to fully assess the safety of our water.

“Drinking water contains complex mixtures of contaminants, yet government agencies currently assess the health hazards of tap water pollutants one by one,” said Sydney Evans, lead author of the paper and a science analyst at the Environmental Working Group. “In the real world, people are exposed to combinations of chemicals, so it is important that we start to assess health impacts by looking at the combined effects of multiple pollutants.”

It’s common to use a cumulative approach to assess the health impact of air pollutants, but the paper published Wednesday in the journal Heliyon represents the first time the approach has been applied to a national dataset of drinking water contaminants.

The model used for this study builds on a cumulative cancer risk assessment of water contaminants in California and offers a deeper insight into national drinking water quality.

Most of the increased cancer risk identified in the study is due to arsenic, disinfection byproducts and radioactive elements such as uranium and radium.

The study found water systems with the highest risk tended to be those in smaller communities which rely on groundwater. Larger systems aren’t in the clear, however, especially given the high presence of disinfection byproducts.

“The vast majority of community water systems meet legal standards,” said Olga Naidenko, the Environmental Working Group’s vice president for science investigations. “Yet the latest research shows that contaminants present in the water at those concentrations – perfectly legal – can still harm human health. We need to prioritize source water protection, to make sure that these contaminants don’t get into the drinking water supplies to begin with.”

The EPA recommends that consumers learn about their local water quality by contacting their local water supplier and requesting an annual water quality report, sometimes called a consumer confidence report. This can help consumers select a water filtration device targeted to the specific contaminants in their tap water.