A small study presented this week offers one, and it favors the sparkling water. Researchers at Purdue University measured how mouth acidity changed in 20 adults after they drank sugar-sweetened soda, regular unsweetened sparkling water, calcium-fortified sparkling water, and plain water. The full advantage of unsweetened sparkling water over soda is therefore probably larger than this measurement alone shows, but for a reason the study did not test. The central uncertainty is what any of this means over years, which a single-session pH study cannot address. Drink acidic beverages with meals rather than sipping all day, use a straw, rinse with plain water afterward, and keep regular dental checkups.