Officials were continuing to investigate Monday what caused high levels of fluoride in the public drinking water system that serves Madison, Anson and Embden.

In the meantime, the Anson-Madison Water District has stopped fluoridating its water until the problem is identified, Superintendent Matthew Demers said Monday.

The high level of fluoride — an additive aimed at promoting dental health — led to a “do not drink” order for the entire system Friday evening. It was lifted for Madison customers Saturday morning and for users in the other towns that afternoon, around 1:45 p.m.

“There was some malfunction of the chemical feed system that caused the overfeed,” Demers said in a phone interview.

Testing Friday showed a level of 5.0 milligrams per liter, Demers said. That exceeded the 4.0 mpl maximum set in federal guidelines, he said.

The district typically aims for a fluoride concentration of 0.7, and water typically tests in the range of 0.5-1.2, Demers said. Staff tests the water for fluoride every day.

“During regular plant checks Friday, District staff identified a potential issue with the fluoride treatment system,” the district said in a news release Monday. “Follow-up testing confirmed fluoride levels above the District’s normal operating level. Staff immediately shut down the fluoride feed system and began flushing water from the treatment facility and distribution system.”

The district sources its water from Hancock Pond in Embden. Fluoride is added to the water after filtration at the treatment plant, also in Embden. From there, water flows by gravity to North Anson, and then on to Anson and Madison.

“District staff and additional personnel worked throughout Friday night and into Saturday morning to isolate the affected portion of the system, flush the water mains and conduct testing at multiple locations,” the district said its news release. “Testing allowed crews to determine where the affected water had traveled and confirmed that it had not reached the Anson Reservoir.”

That is why the order was lifted in Madison first, Demers said. Madison was the farthest away from the source of the excess fluoride.

While they lifted the order initially in Madison, district officials decided it would be clearer for the public to keep the order in effect for all of Anson and Embden, rather than list specific addresses in Anson that were unaffected, Demers said.

The district worked with the state Drinking Water Program throughout the testing and flushing.

The Somerset County Emergency Management Agency and Anson’s local emergency management staff made bottled water available while the order was in effect.

Demers said he had not yet talked to the district’s board about what people can do if they feel they were affected by the “do not drink” order, such as if someone bought their own bottled water.

“If you are concerned about your health or your family, call your health care provider,” the district said in a notice to customers.

The quasi-governmental Anson-Madison Water District has about 2,100 service connections throughout the three towns it serves. It is governed by a board of trustees who are elected by voters in Anson and Madison. 

Since the end of 2021, amid the controversy that led to ultimately-dismissed criminal charges against former Superintendent Michael Corson, the board has contracted with the Richmond-based Maine Rural Water Association to operate the district.

Sixty-five public water systems in Maine, serving 133 communities and 520,000 people, fluoridate their water as a public health measure for reducing the incidence of dental cavities, according to the Maine Center for Disease Control and Prevention Drinking Water Program, part of the state Department of Health and Human Services.

The decision to fluoridate a water supply is made at the local level, the Maine CDC says. Neither the Environmental Protection Agency nor the state requires it.

Fluoride can also enter drinking water from the erosion of natural deposits in the bedrock or from discharges from fertilizer and aluminum factories, according to the Maine CDC.

Anson and Madison have had fluoridated water supplies since 1983, Maine CDC records show. Embden has had a fluoridated water supply since 1981.

The Maine CDC says excessive exposure to the chemical over a lifetime can cause increased likelihood of bone fractures in adults and may cause bone pain and tenderness. In children younger than 8 years old, excessive fluoride can negatively affect teeth.

“It is important to note, however, that fluoride is a chronic (not acute) contaminant, meaning that negative effects may occur only after extended exposure,” Maine DHHS spokesperson Lindsay Hammes said in a statement.

Critics of fluoridated drinking water — including U.S. Health and Human Services Secretary Robert F. Kennedy Jr. and other followers of the “Make America Healthy Again” movement — have long pointed to a host of other health risks they believe come with exposure to fluoride, including neurodevelopmental issues.

The U.S. EPA has undertaken what it calls an expedited review of new scientific information on potential health risks of fluoride in drinking water, using “gold standard science.” The agency says the maximum level of 4.0 milligrams per liter was set in 1986 and most recently reviewed in 2024.