The Maine Center for Disease Control and Prevention has lowered the state limit on forever chemicals, or PFAS, in drinking water to align with rigorous federal standards established by the Biden administration.

The change reduces the maximum amount of the two most harmful forever chemicals to four parts per trillion (ppt) — roughly four drops in 20 Olympic-sized swimming pools — and no more than 10 ppt, for three others combined.

The new rule, adopted in December, will be rolled out in phases, from monitoring by 2027 to initial enforcement in 2028. When in full effect, Maine’s 1,900 public drinking water systems could face fines of up to $2,000 per day for exceeding the maximum contaminant limits.

“The (Department of Health and Human Services) has determined that these new requirements are necessary to protect public health,” it wrote in a rule summary. “The department will work with stakeholders to provide technical assistance and guidance where needed.”

Maine’s old limit was 20 ppt for the combined sum of six forever chemicals. The two most harmful, PFOA and PFOS, are now capped at four ppt each, which is a sharp decrease because they account for the bulk of most forever chemical readings in Maine.

Systems have until April 2029 to comply, which could require treating water, drilling new wells or hooking up to a clean water supply. Until then, Maine will use its 20 ppt limit to “cover the gap,” said DHHS spokeswoman Lindsay Hammes.

Forever chemicals have been used since the 1940s in consumer products and industry, including in nonstick pans, food packaging and firefighting foam. Even trace amounts are deemed harmful, linked to a host of health problems that range from immune deficiency to certain cancers.

State public health officials estimate it could cost $50 million to bring Maine’s public drinking water systems into full compliance with the new standard. The state plans to tap the federal safe drinking water revolving loan fund to cover those costs.

Maintaining each system could cost between $1,000 to $100,000 a year, public health officials predict.

An analysis of state data from 2023 by Defend Our Health, a Portland environmental nonprofit, determined that one in 10 Mainers — roughly 134,035 people — drinks from a public water supply that exceeds the limit Maine just adopted, including in Augusta, Sanford and Waterville.

The group’s data showed that more than 14,000 students and staff at 60 Maine schools, day cares, and colleges are drinking water that was below Maine’s old limit but are above its new limit, like Lake Region High School in Naples or Marshwood Middle School in Eliot.

The U.S. Environmental Protection Agency adopted its protective PFAS limits in April 2024. It said the limit would prevent thousands of premature deaths, serious adult illnesses, and immune and developmental impacts to children.

Private well owners remain responsible for ensuring their water is safe to drink. The quality and safety of private domestic wells are not regulated by the federal government, nor by most state laws. About half of Maine’s residents gets their drinking water from a private well.

Two of the four forever chemicals that had been regulated under the old state rule, PFDA and PFHpA, will not be regulated under the new rule. They are used in food packaging and stain-resistant coatings on rugs and furniture.

Advocates wanted these to count toward the new state limit, but officials say it’s not necessary; they only occur when there is too much PFOA or PFOS anyway. The state will still require the systems to monitor for these chemicals even though they won’t count toward the cap.

The new rule will also require Maine water systems to regulate two new forever chemicals: GenX and PFBS. These chemicals were created to replace PFOA and PFOS but have been found to pose similar health concerns.

Previously, the EPA had advised but not required a drinking water limit of 70 ppt. Many of Maine’s other PFAS advisory levels for milk, eggs, beef, crops, hay, fish or game are based on this old advisory.

State officials said they will use the new EPA standard, and the science supporting it, to inform Maine’s PFAS standards in other substances, but said it would happen over time, and that no one should expect Maine’s milk, beef and fish consumption advisories to change soon.

Maine has identified more than 600 residential wells near former sludge fields, military bases and industrial sites that test above Maine’s old PFAS limit, and that amount is likely to double under the new standard.

The Maine Department of Environmental Protection could not be reached for an interview about how the new limit will be used when deciding who among those living on sludge-impacted land will have their water remediation costs covered by the state.