Seltzer water hydrates you just as well as still water, with a few extra effects worth knowing about. It can ease digestive discomfort, it’s mildly acidic enough to warrant some dental awareness, and it may temporarily make you feel more bloated or hungry. Here’s what happens in your body when you drink it.
Seltzer vs. Club Soda vs. Tonic Water
Seltzer is the simplest option in the sparkling water aisle. It’s plain water with added carbon dioxide and nothing else. Club soda contains added minerals and salts like sodium bicarbonate and potassium sulfate, which give it a slightly different taste and mouthfeel. Sparkling mineral water is similar to club soda, but its minerals come naturally from the spring rather than being added during production.
Tonic water is the odd one out. It’s sweetened (usually with corn syrup in the U.S.) and contains quinine, which gives it that distinctive bitter flavor. A serving of tonic water can have as many calories and as much sugar as a soft drink. If you’re reaching for something to replace soda, plain seltzer is the one that’s essentially calorie-free and additive-free.
It Hydrates You the Same as Still Water
Carbonation doesn’t reduce how well water hydrates you. Studies measuring the short-term hydration potential of different beverages have found that sparkling water performs the same as flat water. The carbon dioxide bubbles don’t interfere with fluid absorption or cause you to lose water faster. If you find it easier to drink enough water when it’s fizzy, that’s a net positive for your hydration.
One caveat: the bubbles can make you feel full faster, which might mean you drink less during intense exercise. For everyday hydration, though, seltzer and still water are interchangeable.
It Can Help With Digestion and Constipation
This is one of seltzer’s more surprising benefits. In a controlled study of people with functional dyspepsia (chronic indigestion) and constipation, drinking carbonated water significantly improved both conditions compared to tap water. Dyspepsia scores dropped from about 7.9 to 5.4 after two weeks of carbonated water, while tap water produced no change. Constipation scores dropped from 16.0 to 12.1 with carbonated water, again with no meaningful improvement in the tap water group.
Carbonated water also improved gallbladder emptying, which helps your body digest fats more efficiently. The gallbladder contraction rate jumped from about 40% to nearly 54% in the carbonated water group. If you deal with sluggish digestion or irregular bowel movements, seltzer may genuinely help.
What Happens to the Gas in Your Stomach
When you swallow carbonated water, the dissolved carbon dioxide is released as gas once it hits the warmth of your stomach. If the expanding gas creates enough pressure, it triggers a belching reflex. This is why seltzer makes you burp more than flat water.
Bloating and discomfort typically only show up when you drink more than about 300 ml (roughly 10 ounces) of a carbonated beverage in one sitting. Below that threshold, most people won’t notice any gastric distress. The carbon dioxide is almost entirely absorbed before it reaches your lower digestive tract, so it’s unlikely to cause intestinal gas or flatulence.
The Effect on Your Teeth
Seltzer is acidic, but not nearly as acidic as soda. When carbon dioxide dissolves in water, it forms carbonic acid, which lowers the pH. Commercial carbonated waters typically range from a pH of about 4.2 to 5.9. Enamel begins to dissolve at a pH below 5.5, which means some seltzers fall right around that critical threshold while others sit safely above it.
Flavored seltzers are a bigger concern. Lemon, lime, and citrus flavors often contain citric acid, which pushes the pH lower and increases the erosive potential. Sports drinks, fruit juices, and regular sodas are all significantly more acidic than plain seltzer, so context matters. Plain seltzer is a massive improvement over soda for your teeth, but it’s not as gentle as still water.
A few practical habits reduce the risk: don’t sip seltzer slowly over hours (prolonged acid exposure is worse than a quick drink), don’t swish it around your mouth, and wait about 30 minutes before brushing your teeth after drinking anything acidic, since brushing softened enamel can cause more damage.
It Won’t Weaken Your Bones
The old concern that carbonated drinks leach calcium from bones applies to cola, not seltzer. The mechanism behind cola’s association with lower bone density involves phosphoric acid, caffeine, and the sugar or sodium that increase calcium loss through urine. Plain seltzer contains none of these. There is no evidence that the carbonation itself, the dissolved carbon dioxide, has any negative effect on bone mineral density or calcium absorption.
It Might Make You Hungrier
One animal study found that rats drinking carbonated beverages had elevated levels of ghrelin, the hormone that signals hunger, and ate more food than rats drinking flat beverages. A parallel experiment in 20 healthy men showed the same ghrelin spike after drinking carbonated drinks. The researchers suggested that the carbon dioxide itself, not the sugar or flavorings, triggered the hormonal response.
This is still a single study, and the effect size in humans hasn’t been well characterized. But if you notice you feel hungrier after drinking seltzer, there may be a real physiological reason. It’s worth paying attention to, especially if you’re using seltzer as a strategy to feel full between meals and finding it doesn’t work as well as you expected.
Sodium in Club Soda and Mineral Water
Plain seltzer contains no sodium. Club soda and some mineral waters do, and the amounts vary by brand. For most people this is negligible, but if you’re on a sodium-restricted diet for blood pressure or heart health, check labels carefully. The Cleveland Clinic notes that tap water is the healthier choice for people actively trying to limit sodium. If you’re drinking plain seltzer, this isn’t a concern at all.