From FDA.GOV
Flavored Water and Nutrient-Added Water Beverages
New types of flavored and/or nutrient-added water beverages have begun to appear in stores and on food service menus. Some are simply bottled water with flavoring, others may also contain added nutrients such as vitamins, electrolytes like sodium and potassium, and amino acids. The bottled water ingredients of these flavored and nutrient-added water beverages must meet the bottled water requirements if the term "water" is highlighted on the label as in, for example, a product named Berry Flavored Spring Water Beverage. In addition, the flavorings and nutrients added to these beverages must comply with all applicable FDA safety requirements and they must be identified in the ingredient list on the label.