Tap water in Charleston and some surrounding areas will be without cavity-fighting fluoride for most of this year, Charleston Water System officials said Friday.

The water system has not been fluoridated since November, when a leak was found in one of the tanks in Hanahan that holds the fluosilicic acid added as a water supplement.

Fluosilicic acid can be used to fluoridate water, but by itself the chemical can produce as a by-product toxic fluorine gas, so the leaking tank had to be taken off line.

While waiting for repairs to the leaking tank, water system officials found that a larger holding tank was also leaking.

As a result, there won’t be any fluoride in the system’s water until at least this fall.

The Charleston Water System serves the greater Charleston area, including the peninsula, West Ashley, Hollywood, Meggett, James Island, North Charleston, Daniel Island, Hanahan and Ladson.

In addition, St. Johns Water Co. buys water in bulk from the Charleston Water System, and Mount Pleasant Waterworks gets about half its water from the Charleston utility.

Three years ago, when the Charleston Water System also temporarily stopped adding fluoride to the water due to a tank leak, public health officials said not to worry.

“It’s not the end of the world,” Mark Barry, associate dean for clinical affairs at the MUSC College of Dental Medicine, said at the time. “What I would be concerned about is that people freak out and take too much fluoride.”

Some foods and beverages already contain fluoride, which is naturally present in some water supplies. In coastal South Carolina, some well water contains so much fluoride that it must be removed through treatment.

The right amount of fluoride helps prevent cavities, but if children whose teeth are still developing get too much fluoride, perhaps by swallowing toothpaste or drinking high-fluoride well water, it can cause permanent stains or pitting of the teeth, officials said. In children and adults, long-term exposure to excessive amounts of fluoride can cause a bone disease called skeletal fluorosis.

Fluoride supplements and topical treatments are available from dentists.

“With my kids, I would just have them brush their teeth,” Barry said during the previous fluoride outage.

In a typical year, the Charleston Water System spends about $150,000 adding fluoride to the water supply. Roughly two thirds of public water supplies in the United States are fluoridated.