The chemicals once seemed near magical, able to repel water, oil and stains.

By the 1970s, DuPont and 3M had used them to develop Teflon and Scotchgard, and they slipped into an array of everyday products, from gum wrappers to sofas to frying pans to carpets. Known as perfluoroalkyl substances, or PFAS, they were a boon to the military, too, which used them in foam that snuffed out explosive oil and fuel fires.

It’s long been known that, in certain concentrations, the compounds could be dangerous if they got into water or if people breathed dust or ate food that contained them. Tests showed they accumulated in the blood of chemical factory workers and residents living nearby, and studies linked some of the chemicals to cancers and birth defects.

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Now two new analyses of drinking water data and the science used to analyze it make clear the Environmental Protection Agency and the Department of Defense have downplayed the public threat posed by these chemicals. Far more people have likely been exposed to dangerous levels of them than has previously been reported because contamination from them is more widespread than has ever been officially acknowledged.

Moreover, ProPublica has found, the government’s understatement of the threat appears to be no accident.

The EPA and the Department of Defense calibrated water tests to exclude some harmful levels of contamination and only register especially high concentrations of chemicals, according to the vice president of one testing company. Several prominent scientists told ProPublica the DOD chose to use tests that would identify only a handful of chemicals rather than more advanced tests that the agencies’ own scientists had helped develop which could potentially identify the presence of hundreds of additional compounds.

The first analysis, contained in an EPA contractor’s PowerPoint presentation, shows that one chemical — the PFAS most understood to cause harm — is 24 times more prevalent in public drinking water than the EPA has reported. Based on this, the Environmental Working Group, an advocacy organization whose scientists have studied PFAS pollution, has estimated that as many as 110 million Americans are now at risk of being exposed to PFAS chemicals.

In the second analysis, ProPublica compared how the military checks for and measures PFAS-related contamination to what’s identified by more advanced tests. We found that the military relied on tests which are not capable of detecting all the PFAS chemicals it believed to be present. Even then, it underreported its results, sharing only a small part if its data. We also found that the military’s own research programs had retested several of those defense sites using more advanced testing technology and identified significantly more pollution than what the military reported to Congress.

Even before the troubling new information about PFAS chemicals emerged, the government had acknowledged problems relating to them were spreading. Past EPA water testing, however incomplete, identified drinking water contamination across 33 states that Harvard researchers estimated affected some 6 million people. The military suspected drinking water at more than 660 U.S. defense sites where firefighting foam was used could be contaminated; earlier this year, it announced it had confirmed contamination in 36 drinking water systems and in 90 groundwater sites on or near its facilities.

The new analyses suggest these findings likely represent just a fraction of the true number of people and drinking water systems affected.

In written responses to questions, the EPA did not directly address whether it had understated contamination from PFAS chemicals. The agency said it had confidence in its current testing procedures and had set detection limits at appropriate levels. It also stated that it is taking steps towards regulating some PFAS compounds and registering them as “hazardous substances,” a classification that triggers additional oversight under waste and pollution laws.

The agency will “take concrete actions to ensure PFAS is thoroughly addressed and all Americans have access to clean and safe drinking water,” then-EPA Administrator Scott Pruitt, who recently resigned, said in the written statement to ProPublica in May.

The Department of Defense also responded to questions in writing, defending its testing methods as the best available and calling it difficult to fully assess risks from PFAS because the EPA has not regulated these chemicals. A DOD spokeswoman said the Pentagon’s research group has a program underway aimed at enhancing the test methods and detecting more PFAS compounds, but suggested that no alternatives were ready for use. She did not answer questions about why the agency reported contamination levels for only two chemicals to Congress when it would have had data on many more, stating only that the Pentagon “is committed to protecting human health and the environment.”

Environmental experts aren’t convinced.

“Widespread contamination may be harming the health of millions or even tens of millions of Americans and the government is intentionally covering up some of the evidence,” said Erik Olson, a senior director for health, food and agriculture initiatives at the Natural Resources Defense Council, in an interview. The EPA and Defense Department “have done all they can to sort of drag their feet and avoid meaningful regulatory action in making significant investment in cleanups.”

In May, a Politico report revealed that the EPA and the White House, along with the Defense Department, had pressured a division of the Centers for Disease Control and Prevention to withhold a health study expected to warn that people exposed to PFAS chemicals face greater health risks than were previously understood. That report was quietly released in mid-June and, indeed, estimated safe levels of exposure are seven to 10 times smaller than what the EPA has said.

Such a determination could spur stricter limits on exposure than the EPA appears to have considered. Paired with an emerging realization that testing by the EPA and DOD hasn’t captured the true extent of contamination, the government could be forced to reconceive its approach to these compounds, said David Sedlak, the director of the Institute for Environmental Science and Engineering at the University of California, Berkeley, who helped develop one of the most advanced commercial tests for PFAS substances.

“Not talking about it isn’t going to make the problem go away,” Sedlak said. “And because these compounds are forever — they aren’t going to degrade on their own — eventually there is going to be a day of reckoning.”

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