Fluoride is a mineral that occurs naturally in many foods and water. Fluoride helps prevent tooth decay by making your tooth enamel more resistant to acid attacks from plaque bacteria in your mouth. Fluoride can also reverse early decay. City water often contains fluoride, so by drinking tap water, you will acquire fluoride. If your drinking water does not have fluoride, supplements are available. Talk to your dentist or dental hygienist about whether you are getting the daily amount of fluoride you need. The ADA recommends fluoride for adults as well as children.