A report from the Environmental Working Group (EWG) found that the tap water of 218 million Americans contains levels of chromium-6. Chromium-6, or hexavalent chromium, are a pack of carcinogens that were at the center of the film’s legal case. The National Toxicology Program describes chromium as a naturally occurring element present in various states. Trivalent chromium is most commonly found in nature and proposed to be an essential nutrient. Hexavalent chromium compounds are the next most stable forms of chromium. However, hexavalent chromium rarely occurs naturally and is typically associated with industrial sources.

In 2008, a two-year study by the National Toxicology Program found that drinking water with chromium-6 caused cancer in laboratory rats and mice. In humans it has been linked to lung cancer, liver damage, reproductive problems and developmental harm.

Between 2013 and 2015, the Environmental Protection Agency (EPA) ordered utility companies to test for chromium-6 in drinking water. The EWG report came after utilities took more than 60,000 samples of drinking water and found chromium-6 in more than 75 percent of them.

The EPA regulates the level of contaminants in drinking water “at which no adverse health effects are likely to occur.” The current federal drinking water standard for total chromium is 0.1 mg/l or 100 ppb (that includes chromium-3 and chromium-6.) While the EWG report shows low levels of chromium-6 in drinking water, research shows that even at low levels of exposure the carcinogen can be dangerous.

States have responded differently to regulating chromium-6.

In July of 2014, California set a public health goal of “0.010-milligram per liter MCL for hexavalent chromium equivalent to 10 micrograms per liter (µg/L),” making it the only state with a legally enforceable limit in drinking water. Yet California has one of the highest average statewide levels, according to the EWG analysis. In 2011, California’s Office of Environmental Health Hazard Assessment set a public health goal of 0.02 parts per billion. EWG’s report says those levels “would pose negligible risk over a lifetime of consumption.” It illustrates that: “one part per billion is a single drop in an Olympic-size swimming pool.”

New England’s water showed very low levels of chromium-6 and the source of where it’s coming from isn’t clear. That’s made it hard for officials to treat the water. Rhode Island Public Radio reports, “there’s some evidence that certain chemicals used to make drinking water safer could actually cause the nutrient chromium-3 to convert to chromium-6. Or it could be leaching from distribution pipes.”

In Pennsylvania’s Borough of State College, the EWG study found an average of 0.37 ppb in 24 samples, the highest containing 0.60 ppb. John Lichman, the Executive Director for State College Burrough Water Authority told The Daily Collegian, “We’re aggressively replacing our infrastructure that needs to be replaced. What good is having the greatest, most pristine drinking water in the world if you’re putting it through a hundred year old system? We don’t want State College to end up like Flint, Michigan.” Flint has been at the epicenter of water contamination from chromium-6 and other toxic elements.

The EWG estimates that if left untreated, chromium-6 in tap water will cause more than 12,000 excess cases of cancer by the end of the century.

So, is it possible to get chromium out of the water at home? Yes, but it comes with drawbacks. PBS’s News Hour interviewed Ian Webster, president of Project Navigator, an environmental engineering project management company that represented the Hinkley community (of the Erin Brokovich case.) He says, “there are filters you can buy to remove the chemical from your tap water. The most effective way to remove chromium-6 from drinking water is with an ion exchange water treatment unit.” It also removes arsenic and manganese. The unit must be maintained regularly to maintain its effectiveness and its maintenance can be expensive.

In the meantime, researchers from Arizona State University, Yale University, University of Texas at El Paso and Rice University have teamed with private industry to create a water filter for chromium that promises to be easier to use and less expensive.

If in doubt about drinking tap water, go for filtered bottled water. The CDC offers an extensive guide to keeping your drinking water safe.