Seltzer water hydrates you just as effectively as plain water. The only difference is dissolved carbon dioxide gas, which creates the bubbles. Your body processes the water content identically, and seltzer counts fully toward your daily fluid intake. That said, the carbonation does introduce a few minor differences worth knowing about.
Hydration: No Measurable Difference
Researchers have directly compared sparkling and still water using something called the beverage hydration index, which measures how much fluid your body actually retains after drinking. Sparkling water scored identically to regular water. Your kidneys don’t care whether the water arrived with bubbles or without.
The CDC lists sparkling water and seltzers alongside plain water as low-calorie hydration choices. If you prefer the fizz and it helps you drink more throughout the day, there’s no hydration penalty for choosing seltzer over tap.
What Seltzer Actually Is
Seltzer is plain water with pressurized carbon dioxide injected into it. That’s it. No added minerals, no sodium, no sweeteners. It’s the simplest form of carbonated water you can buy.
This makes it different from other bubbly drinks that often get lumped together:
- Club soda contains added minerals like sodium chloride and sodium bicarbonate. A 16-ounce can has roughly 100 milligrams of sodium, which gives it a slightly salty taste.
- Sparkling mineral water comes from natural springs and contains dissolved minerals like calcium, magnesium, and sodium. The FDA requires at least 250 parts per million of dissolved solids from the bottling source.
- Tonic water is a completely different product. It contains quinine (a bitter compound from tree bark) along with sugar or high-fructose corn syrup. A can of tonic water has calories comparable to a soft drink.
If you’re watching sodium intake, plain seltzer is the safest bet among carbonated options. Club soda’s sodium content is modest, but it adds up if you’re drinking several cans a day.
The Tooth Enamel Question
When carbon dioxide dissolves in water, it forms a weak acid called carbonic acid. This drops the pH of seltzer to somewhere between 4 and 5, making it more acidic than plain water (which sits around 7). Tooth enamel starts to soften below a pH of about 5.5, so seltzer does land in a mildly erosive range.
In practice, the risk is small for unflavored seltzer. The acidity is far weaker than what you’d get from orange juice, soda, or sports drinks. Flavored seltzers are a different story. Brands that add citric acid for a lemon or lime taste push the pH lower and become meaningfully more erosive over time. If you drink flavored seltzer regularly, sipping through a straw or rinsing with plain water afterward reduces contact with your teeth.
Effects on Digestion and Appetite
The carbon dioxide in seltzer expands in your stomach, which is why carbonated water can make you feel fuller than the same volume of still water. Some research suggests this increased sense of fullness may help people eat slightly less throughout the day.
One small animal study raised concerns that carbonated water might increase levels of ghrelin, a hormone that stimulates hunger. But that finding hasn’t been replicated in human research. The broader evidence points in the opposite direction: sparkling water tends to help control hunger rather than stimulate it. If you experience bloating or discomfort after drinking seltzer, that’s a normal reaction to the gas, not a sign of harm. People with irritable bowel syndrome or acid reflux may find the bloating aggravates their symptoms.
Bone Health Isn’t a Concern
The idea that carbonated drinks weaken bones has been around for years, but the evidence points squarely at cola, not carbonation itself. A clinical trial published in the British Journal of Nutrition compared postmenopausal women who drank about a quart of carbonated mineral water daily with those who drank the same amount of still water. After eight weeks, there was no difference in markers of bone breakdown between the two groups.
Larger studies have found the same pattern. Non-cola carbonated drinks showed no association with lower bone mineral density. Cola was linked to lower density at the hip in women, but researchers attributed this to the caffeine in cola rather than the carbonation. Plain seltzer doesn’t appear to contribute to osteoporosis or increase fracture risk.
Where Seltzer Falls Short
Tap water in many areas contains added fluoride, which strengthens tooth enamel over time. Most bottled seltzer does not. If seltzer is your primary water source throughout the day, you may be getting less fluoride than someone drinking tap water. This matters most for children whose teeth are still developing.
Plain water also has a neutral pH, so it never works against your enamel. And it’s free. Seltzer’s practical downside is cost: drinking four or five cans a day adds up compared to filling a glass from the faucet. For people who genuinely dislike still water, though, the tradeoff is worth it. Staying well hydrated with seltzer is far better than being chronically underhydrated because plain water doesn’t appeal to you.