Fresca is a crisp grapefruit-flavored soft drink (registered trademark by Coca-Cola) while aguas fresca are soft drinks made with different flavors (watermelon, mango, banana, strawberry etc.). The word "fresca" as such is italian and means "fresh", made out of natural ingredients in the context of e.g."pasta fresca". Depending now in which context the text is (if rather mexican or italian) I would pick the translation accordingly. Hope this helps!