OKLAHOMA CITY -- Experts recommend eight to 12 glasses of water per day to maintain health and to get an added boost of fluoride to improve smiles.

However, officials say that almost 90 percent of Oklahoma towns don't add fluoride to city tap water.

Dr. Mike Morgan said the recommended level by the U.S. Public Health Service is one milligram of fluoride per liter of water.

"Fluoridation at optimal levels is safe, is cost-effective and actually works," Morgan said of the naturally occurring mineral. "It reduces dental decay for both children and adults."

The American Dental Association's official position on fluoride is that it is completely safe for humans if controlled at below-recommended levels. Detractors of the mineral claim that it's responsible for osteoporosis, bone cancer and kidney problems.

"In some higher levels, we're talking very, very high levels, you can have some discoloration of the teeth," Morgan said.

The Department of Environmental Quality is responsible for making sure water supplies in cities that supplement with fluoride are tested twice a day. They must submit a sample once a month.

"If the municipality exceeds the recommended level of two milligrams per liter, then they are required to give public notice. In other words, they send out to all their customers a letter saying we have exceeded the standards, telling them what it is and usually telling them what methods they'll take to reduce it," said DEQ spokeswoman Monte Elder.

However, that standard is merely a recommendation. The DEQ cannot impose penalties for a high level.

While fluoride is readily available in toothpaste and mouthwashes, the debate over whether the benefits of the mineral outweigh its risks will continue.