I'm not sure of the exact brand you're referring to off the top of my head, but if it doesn't have any calories at all, most likely it is sweetened via Nutrasweet. Nutrasweet has been shown to be potentially toxic to brain cells. I didn't realize that before consuming large amounts of Wal-Mart's and K-Mart's generic flavored waters containing Nutrasweet over a period of time while dieting. That explained why I seemed to frequently get headaches after drinking large amounts. Unfortunately, they taste very good too. Now it's just lots of water with added lime, and more frequent brushings to minimize the acidic effect on my teeth.