Plain seltzer water hydrates you just as well as still water and poses no serious health risks for most people. It can affect your digestion, your teeth, and even your swallowing reflexes in ways that are worth understanding, but the overall picture is reassuring. Here’s what actually happens when you drink it.
It Hydrates You Like Still Water
The carbonation in seltzer doesn’t reduce its ability to hydrate you. Researchers developed a beverage hydration index to compare how well different drinks maintain fluid balance, and sparkling water performs the same as flat water regardless of sex or body mass. The bubbles might make you drink slightly less in one sitting because of the fullness they create, but the water itself is absorbed and used by your body identically.
How It Affects Your Stomach and Digestion
When carbon dioxide dissolves in water, it forms a weak acid called carbonic acid. Once you swallow it, the CO2 expands as it warms in your stomach, which is why seltzer can make you feel temporarily bloated or gassy. Studies show that carbonated water doesn’t change how quickly your stomach empties overall, but it does shift where food sits inside the stomach, pushing more of the meal into the upper portion. That temporary distension in the upper stomach is what creates the sensation of fullness.
For people dealing with chronic indigestion or constipation, the news is surprisingly positive. In a clinical trial, participants who drank carbonated water for several weeks saw meaningful improvements in both conditions. Dyspepsia scores dropped from about 7.9 to 5.4, while constipation scores fell from 16.0 to 12.1. The tap water group saw no change. Carbonated water also improved gallbladder emptying, which plays a role in digestion after meals.
If you have acid reflux or irritable bowel syndrome, though, the gas release can aggravate symptoms. The distension in your stomach can temporarily lower the pressure at the valve between your esophagus and stomach, making reflux more likely in people already prone to it.
What It Does to Your Teeth
This is where seltzer deserves a closer look. Tooth enamel begins to dissolve at a pH of about 5.5, and plain carbonated water typically falls in the range of 3.5 to 4.5, which is below that threshold. That sounds alarming, but context matters. The carbonic acid in plain seltzer is extremely weak compared to the phosphoric acid in cola or the citric acid in lemon-flavored drinks, and your saliva quickly neutralizes it.
The real concern is with flavored seltzers. Many contain added citric acid for tartness, which lowers the pH further and clings to enamel more aggressively than carbonic acid alone. Drinking flavored seltzer throughout the day, sipping slowly over hours, gives your teeth repeated acid exposure without time to recover. If you drink a lot of it, using a straw and rinsing with plain water afterward can reduce contact with your enamel.
No Evidence It Weakens Your Bones
The idea that carbonated drinks leach calcium from your bones has persisted for years, but the evidence points squarely at cola, not seltzer. A large study found that cola intake was associated with lower bone mineral density at the hip in women, but non-cola carbonated drinks showed no such association. The likely culprit in cola is phosphoric acid, not carbonation itself.
A clinical trial published in the British Journal of Nutrition tracked healthy postmenopausal women, a group particularly vulnerable to bone loss, who drank about a quart of carbonated mineral water daily for eight weeks. Blood and urine markers of bone turnover were identical to those in women drinking the same amount of flat water. Seltzer does not contribute to osteoporosis or increase fracture risk.
It May Suppress Hunger Hormones Slightly
Carbonation appears to influence ghrelin, the hormone that signals hunger. In one study, drinking a non-caloric carbonated beverage before a solid meal reduced ghrelin levels to roughly the same degree as drinking plain water. A non-carbonated version of the same beverage produced a smaller ghrelin drop. The practical effect was modest: despite the hormonal shift, participants didn’t actually eat less food. So while seltzer may briefly take the edge off hunger, it’s not a meaningful appetite suppressant.
It Can Help People Who Struggle to Swallow
One of the more interesting findings involves people with swallowing difficulties, a condition called dysphagia that’s common after strokes and in neurodegenerative diseases. The fizz in carbonated water activates touch and chemical receptors in the throat that still water doesn’t reach. This extra sensory input signals the brain’s swallowing centers more intensely, which can help trigger a stronger, more coordinated swallow. Multiple studies have confirmed that carbonated liquids benefit the swallowing reflex in people with neurological damage, making them a simple therapeutic tool.
Kidneys Are Fine With Plain Seltzer
Research linking carbonated beverages to kidney stones and chronic kidney disease has focused on sugar-sweetened sodas and colas specifically. Cola contains phosphoric acid, which changes urine composition in ways that promote calcium oxalate stone formation. In a randomized trial, men with a history of kidney stones who kept drinking phosphoric acid beverages had higher recurrence rates than those who switched to citric acid drinks. Plain seltzer water contains neither phosphoric acid nor sugar, so it doesn’t carry the same risk. Staying well-hydrated with any type of water is one of the most effective ways to prevent kidney stones.
Plain vs. Flavored vs. Club Soda
Not all bubbly water is the same, and the differences matter for your body.
- Plain seltzer is just water plus carbon dioxide. It contains no sodium, no calories, and no sugar.
- Flavored seltzer adds flavor compounds and often citric acid, which increases acidity and can be harder on tooth enamel. Most flavored seltzers still have zero calories and no sodium.
- Club soda contains added minerals like sodium bicarbonate and potassium sulfate, which give it a slightly salty, mineral taste. If you’re watching sodium intake, check the label.
- Sparkling mineral water comes from natural springs and contains varying levels of calcium, magnesium, and sodium depending on the source.
For the most neutral impact on your body, plain unflavored seltzer is the cleanest option. It gives you the same hydration as tap water with no meaningful downsides beyond temporary bloating if you drink a lot at once.