The U.S. Environmental Protection Agency is adding some "forever chemicals" to the list of toxins in drinking water that must be reported. That is going to require a lot of infrastructure investment.

"We are now in the process of establishing a drinking water standard for about six different PFAS," Radhika Fox, assistant administrator for the EPA's Office of Water, told CNBC. PFAS is an abbreviation for per- and polyfluoroalkyl substances.

The EPA is considering a rule that would require tap water utilities to report information about the levels of PFAS above four parts per trillion in drinking water. The rule has not been finalized.

"These per- and polyfluorinated alkyl substances, they're made by different companies that take fluorine and they attach it to two carbon molecules and they stick around forever. That's why they got the nickname 'forever chemicals,'" explained Tom Neltner, senior director of safer chemicals at the Environmental Defense Fund.

PFAS are chemicals that have been released into the environment through textile manufacturing, plating facilities, and aviation manufacturing as well as plastics, resins, molds, and more, according to the Utah Department of Environmental Quality.

Cheryl Norton, chief operating officer for American Water, the largest publicly traded water and wastewater utility company in the country, said meeting this reporting requirement is going to be expensive. "It's going to cost about $47 billion in infrastructure investments across the U.S. to treat for PFAS at four parts per trillion. And we think that the ongoing costs are going to be about $700 million a year."

About 300 million people in the U.S. receive their water from a public water system, according to the EPA. At least 45% of tap water in the U.S. is known to have PFAS in it, according to the U.S. Geological Survey.

"We have been monitoring for PFAS for some time, and we see that it's occurring in drinking water systems at levels of concern," said Fox.

"Not only is it a carcinogen, but that chemical also undermines our immune system. It undermines the effectiveness of vaccines, which is a big issue," Neltner said.

Sydney Evans, a senior science analyst at the Environmental Working Group, said, "Most tap water is probably not going to have a system set up at the treatment plant where PFAS is going to be able to be treated. In the future, hopefully, that will happen, but at the moment there's still PFAS in a lot of people's water."

In the meantime, Evans says, some additional filtration for water is needed. Most experts agree that filtering the water at home is a temporary solution to a massive health concern.

"We really believe that the people who are responsible for the contamination should have to pay for this, not our customers," said Norton. Without additional funding from Congress, the infrastructure upgrades will likely be funded through the rates consumers pay for water usage.

In addition to the rule the EPA is considering that would require water utilities to report on PFAS, a new EPA rule took effect Nov. 30 that will require companies that manufacture, process, or use some PFAS chemicals to report information about PFAS.

Watch the video above to learn more about how safe tap water is in the U.S.

Correction: This article and video have been updated to reflect that the EPA is considering a rule that would require tap water utilities to report information about the levels of PFAS above four parts per trillion in drinking water. A separate rule took effect Nov. 30 that requires companies that manufacture, process, or use some PFAS chemicals to report information about PFAS. Previous versions of the article and video incorrectly indicated that the water utilities rule was finalized and had taken effect.