On Wednesday, the Environmental Protection Agency finalized limits on certain common types of PFAS chemicals in drinking water. It is the first time a nationwide limit on so-called forever chemicals has been imposed on water providers. EPA Administrator Michael Regan called it the biggest action the agency has ever taken on PFAS, saying the rule will reduce exposure for 100 million people.

The regulation represents a new era for public health and drinking water. The Biden administration has also proposed new rules that would force utilities to remove harmful lead pipes. It’s part of their overall goal to making tap water safer. Utilities are alarmed at these new requirements and the billions of dollars they will cost.

Here are the essential things to know about the family of chemicals and EPA’s latest action:

WHAT ARE PFAS?

PFAS, or perfluoroalkyl and polyfluoroalkyl substances, are a group of chemicals that have been around for decades and have now spread into the nation’s air, water and soil.

They were manufactured by companies such as 3M, Chemours and others because they were incredibly useful. They helped eggs slide across non-stick frying pans, ensured that firefighting foam suffocates flames and helped clothes withstand the rain and keep people dry.

The chemicals resist breaking down, however, which means they stay around in the environment.

SO, WHAT’S THE PROBLEM?

Environmental activists say that PFAS manufacturers knew about the health harms of PFAS long before they were made public. The same attributes that make the chemicals so valuable – resistance to breakdown – make them hazardous to people.

PFAS accumulates in the body, which is why EPA set their limits for drinking water at 4 parts per trillion for two common types — PFOA and PFOS — that are phased out of manufacturing but still are present in the environment. Health experts say low doses of the chemicals can build up in the body over time, so even small amounts are a problem.

There’s a wide range of health harms now associated with exposure to certain PFAS, many largely phased out. Cases of kidney disease, low-birthweight and high cholesterol in additional to certain cancers can be prevented by removing PFAS from water, according to the EPA.

The guidance on PFOA and PFOS has changed dramatically in recent years as scientific understanding has advanced. The EPA in 2016 said the combined amount of the two substances should not exceed 70 parts per trillion. Now the EPA says no amount is safe.

WHAT DOES THE NEW RULE DO?

In short, the rule sets limits on several common types of PFAS. The EPA says there is enough evidence to limit PFOA and PFOS at the lowest level they can be reliably detected.

For some other types, the limit is 10 parts per trillion, and there are also limits on certain PFAS combinations.

Water providers will have three years to test for PFAS. They’ll also need to tell the public if results are too high.

And if results are a concern, utilities have two more years to install treatment. The EPA estimates that 6% to 10% of water systems will have levels above the EPA’s new limits.

As a result of the rule, the EPA says nearly 10,000 fewer deaths will occur in the coming decades and tens of thousands of severe illnesses will be avoided.

WHAT ARE PEOPLE SAYING ABOUT IT?

Well, quite a lot.

Environmental and public health groups have argued that limits should have been in place long ago, but they are generally thrilled with the announcement. They like that it sets limits for PFOA and PFOS at very low level s and that the agency did not agree with some utility groups that wanted a more lenient limit.

They are happy the Biden administration has finally acted to reduce PFAS in tap water, a source of PFAS that’s easier to address than others. They acknowledge it will cost a lot for communities to install treatment facilities, but say that billions of dollars are available from the infrastructure law and court settlements will provide billions more.

Water providers are not the ones that put PFAS in the environment, but now they face mandates to remove it. That’s going to be a big change for them.

They’ve said the EPA’s $1.5 billion annual cost estimate is too low, water bills for consumers will go up and the health benefits of the rule aren’t big enough, especially at low PFAS concentrations, to justify all the expense.

In addition, they say this rule will hurt small communities that have fewer resources and will have a harder time complying.

Then there are the practical challenges. Utilities say they will struggle to find enough experts and workers and the material needed to remove PFAS.

And there are concerns that consumers who hear about high levels of PFAS in their drinking water might stop consuming tap water altogether, further deteriorating trust in an important public resource.

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