Fluoridated water causes cancer. More than half of Americans drink water that contains fluoride. A connection between fluoride in drinking water and cancer has been debated and studied for many years. The Centers for Disease Control (CDC) summarized extensive research findings and concluded that studies to date have produced "no credible evidence" of an association between fluoridated drinking water and an increased risk for cancer. Fluoridated water and toothpaste help keep teeth firm and more resistant to cavities.