The authority's target fluoride level has increased from 0.80 milligrams per liter to 0.85 mg/L, a difference that General Manager Glenn Page said customers are unlikely to notice.
"It's a very small change," he said. "We're just following the regulatory requirements we have."
Fluoride, which is also found in dental products, helps to prevent tooth decay, and the Centers for Disease Control and Prevention has listed it as one of the top 10 public health achievements of the 20th century. But overexposure at early ages can cause damage to teeth in children under 8, and adults exposed to excessive fluoride over a lifetime may be more at risk of bone fractures, according to the CDC.
For more than 40 years, water systems in Georgia have been required by law to have fluoride levels of at least 0.70 mg/L and no more than 1.2 mg/L, a range set by the CDC and the state Department of Health and Human Services.
But then in January, the CDC lowered its recommended fluoride limit to a flat 0.70 mg/L. The CDC notes on its website that consumers have greater access to fluoride now than when the mandatory fluoridation was started in 1962.
So the water authority dropped its levels to .75 mg/L, to reduce the amount of fluoride while still staying within the state guidelines.
In May however, the Cobb authority received a notice from the Georgia Department of Community Health saying the new level was to be 0.85 mg/L.
"The memo we received from the Department of Community Health was not dated, not signed and indicated it was from the director Brenda Fitzgerald, telling us we had a new target. It was going to be 0.85, which was more than we were used to," Page said.
The authority kept the fluoride level at 0.75 mg/L while it sought direction from the state, he added.
A few weeks later, the authority learned its official fluoride target was 0.85 mg/L, as directed by the nonprofit Georgia Rural Water Association, which the state pays to enforce its fluoridation measures.
Jerry Stapp, a fluoride instructor for the rural water association, said the difference between 0.70 and 0.85 is "like splitting hairs" when it comes to water levels.
"In the water industry and feeding process, you have that kind of fluctuation daily," he said. "Fluoride is a natural thing. We're just trying to optimize it to where it's effective."
Based on studies, the range previously set by the CDC is where fluoride is the most effective at preventing tooth decay, said Stapp.
"Below 0.70 is like a waste of fluoride and anything higher than 1.2 is too much," he said.
Because the levels can fluctuate daily, if the regulatory level were set at 0.70, sometimes the consistencies may fall below that minimum level of effectiveness, Stapp said.
A dilution system at water-treatment plants adds the fluoride, and the levels are tested once per day, as opposed to contaminants, which are tested hourly, Page said.
Fluoridation has become increasingly controversial as national groups urge an end to the mandatory practice, out of fear of fluorosis and other health factors.
The issue will continue to be examined by the federal, state and local agencies though, Page said.
"It's a dynamic thing. They're still waiting for a more firm directive from the federal level. CDC and Health and Human Services are all continuing to study the fluoride issue," he said.
Marietta dentist David Kurtzman said he supports fluoridation in water.
"You're not getting harmed by it more than the other chemicals and things found in the water," Kurtzman said. "Because of fluoride, there was a documented decrease in the amount of dental decay that got better and better until about seven or eight years ago," he said. Increased sugar in food and drinks are partly to blame for the uptick in cavities in recent years, he said.
The Cobb County-Marietta Water Authority is the second largest provider of drinking water in Georgia and provides treated drinking water to Cobb County, Paulding County, the Douglasville-Douglas County Water and Sewer Authority, the Cherokee County Water and Sewerage Authority, Marietta, Smyrna, Austell, Powder Springs, Mountain Park, Woodstock and Lockheed Martin.