More than a hundred drinking water sources across Colorado — ranging from cities and counties to elementary schools and campgrounds — contain what are now considered to be potentially hazardous levels of PFAS, toxic “forever chemicals” linked to a slew of health problems, data from 2020 shows.

And many more drinking water sources across the state are probably similarly contaminated but haven’t yet been tested, experts say, which is cause for concern and immediate action.

RELATED: What are PFAS, or “forever chemicals?”

Not only should water officials in Colorado and the rest of the country, ramp up testing efforts but they should also invest in new ways to clean drinking water, pinpoint contamination sources and cut out products that use the harmful compounds.

“There’s really no safe level of these chemicals,” Linda Birnbaum, former director of the National Institute for Environmental Health Sciences told The Denver Post.

PFAS, a broad chemical group containing thousands of different specific compounds, are linked to cancer, birth defects, diabetes and autoimmune problems.

The Environmental Protection Agency sharply reduced its health advisory levels for the chemicals last month. Those levels are meant as a preliminary warning while the EPA develops more formal and enforceable regulations for the compounds.

Previously acceptable levels for two types of chemicals, one called perfluorooctanoic acid (PFOA) and another called perfluorooctanesulfonic acid (PFOS), sat at 70 parts per trillion. But on June 15 the EPA lowered those levels to .004 parts per trillion for PFOA and .02 parts per trillion for PFOS.

For context, 1 part per trillion amounts to a single drop of chemicals in 500,000 barrels of water, Thornton officials said in a release.

Federal officials recommend that any water provider with PFAS concentrations higher than those trace amounts should notify their customers, EPA spokesman Rich Mylott said. But that notification isn’t specifically required, Mylott said.

A round of state-funded PFAS tests in 2020 showed that more than 100 public drinking water sources in Colorado have concentrations of the chemicals. Under the EPA’s old standard of 70 parts per trillion, most of those sources fell well below the federal health advisory level. Under the EPA’s new standards, however, none of them do.

“Almost everyone is going to exceed the new health advisory levels,” Birnbaum said.

Thornton announced Monday that its drinking water had a concentration of PFOA more than 1,000 times the EPA’s new level. City officials called it a concern but not a crisis.

But Thornton isn’t alone. Arapahoe County, Aurora, Brighton, Crowley County, Sterling, Englewood, Frisco and Lafayette are among those water providers that showed elevated levels of the compounds, data collected by the Colorado Department of Public Health and Environment shows. Schools, campgrounds and fire protection districts also have elevated levels.

Despite the 2020 test results, no action is yet required from any water providers with elevated PFAS levels. The EPA’s new guidelines aren’t legally enforceable and the agency isn’t expected to propose its more formal regulations until later this year. Finalizing those new regulations could take several more years, Birnbaum said.

Increased federal and local scrutiny of PFAS is good but overdue, Philippe Grandjean, adjunct professor of environmental health at Harvard, said. Scientists, regulators and the companies producing these chemicals have known of the risks involved for years or decades.

“This is quite scary when you see these low numbers and you realize that it’s just about everybody that’s exposed to these amounts,” Grandjean said.

Broadly speaking, the experts agreed that four things must now happen. First, more testing is needed to detect contaminated drinking water.

While Thornton already alerted its customers about the chemicals, other places are holding out for additional tests.

For example, in 2020 one source of Aurora’s drinking water tested 800 times higher than the new federal levels for PFOA and 105 times higher for PFOS.

Rory Franklin, a spokeswoman for Aurora, said the city has since improved its ability to clean its water of the compounds but “until we complete our current round of tests, we don’t have the data to show that we have improved.”

Testing equipment also often isn’t sensitive enough to detect such small, but still potentially dangerous, traces of PFAS, Timothy Strathmann, a professor of civil and environmental engineering at the Colorado School of Mines, said.

While tests in the past two years didn’t detect any PFAS in Colorado Springs Utilities’ water, spokeswoman Jennifer Jordan noted that the utility is “not aware of testing technology that allows for accurate testing below 2.0 parts per trillion.”

That’s still 500 times higher than the EPA’s health advisory level for PFOA and 100 times higher for PFOS.

Colorado Springs Utilities is “awaiting further guidance” from the Colorado Department of Public Health and Environment on how to better test their water, Jordan said.

CDPHE officials did not answer questions about whether new rounds of tests are likely or how they plan to overcome that technological barrier.

After new rounds of water tests, providers who find contaminants must then clean their water, Birnbaum said. One method using granular activated charcoal can remove some of the compounds but new ways are needed to clean the water of other types of chemicals, she said.

Cleaning or filtering the water takes time and money, Grandjean added. In the short term, people concerned about their water — especially those who are pregnant, breastfeeding or raising young children — can buy their own filters.

To ensure the water stays free of the contaminants, however, officials must also track down the sources of contamination and clean them up, Grandjean said. That’s another massive and expensive undertaking.

At the same time, Arlene Blum, a scientist and executive director of the California-based nonprofit Green Science Policy Institute, said legislators must work to reduce the amount of PFAS used in everyday products. Not only do the products themselves expose people to the harmful chemicals but the factories that produce them are also significant sources of pollution.

Grandjean praised Colorado’s recent legislation to phase out certain products made with PFAS, but said more work must be done.

And much of that work depends on the EPA’s next steps. Blum said whatever enforceable regulations the federal agency proposes likely won’t be as strict as its health advisory levels.

States like Massachusetts, Michigan, New Jersey, New York and Vermont already have their own regulations for some PFAS ranging from 8 parts per trillion to a combined limit of 20 parts per trillion for a mix of six compounds. Colorado doesn’t have its own regulations for PFAS.

Existing and upcoming regulations for PFAS represent progress, Grandjean said. But much more action is needed to clean drinking water across the country, not to mention combatting other sources of the hazardous chemicals. Those efforts have been put off far too long and they’re only growing more expensive.

“We have to accept that we have ignored this problem for years and we have forgotten that our priorities should be the next generation,” Grandjean said.

Ultimately, Grandjean said, it’s the next generations that will have to pay the price.