Unfortunately, the answer is yes. Flavored water is a sneaky cause of tooth decay. You may be wondering why, since it’s usually sugar-free and there are no artificial sweeteners. The reason is that it’s most often citrus flavored: lemon, lime, grapefruit, and so forth. The citric acid in the flavored water eats away at your tooth enamel, which can cause stains, sensitivity, decay, and cavities.