In a 2019 study, researchers compared the hydration effects of plain water, seltzer, and a sports drink on 72 healthy adults. The verdict? Seltzer and still water performed identically in hydrating the body. None of the participants shriveled into raisins. Another study from the American Journal of Clinical Nutrition found that carbonated water actually improves digestion and may even help you feel fuller—so you’re less likely to chug a sugary soda that would dehydrate you. (See? The bubbles are working double duty.)
The only real caveat is sodium content. Some flavored seltzers or club sodas add salt, which can make you retain water—but that’s not dehydration, it’s just your ankles feeling poetic for a day. Check the label: if it has more than 50 mg of sodium per can, you’re basically drinking a very light mineral water. Still fine, not a crisis.
Seltzer Water Unhealthy
But Wait—Doesn’t Caffeine Cancel It Out?
Ah, you’re thinking of sparkling energy drinks or seltzers with added caffeine (looking at you, trendy “bubly bounce” or whatever). Caffeine is a mild diuretic, meaning it makes you pee more—but the water in the seltzer more than compensates. Studies show that up to 400 mg of caffeine (about 4 cups of coffee) doesn’t cause net dehydration if you’re also drinking fluids. So, unless you’re mainlining 10 cans of caffeinated seltzer while running a marathon in the desert, you’re fine. Your kidneys will just be slightly busier than usual.
