The fizzy water aisle lines up seltzer, club soda, sparkling water, and tonic water on the same shelf, and most shoppers grab whichever bottle looks familiar. The four drinks are not the same thing.
They carry different sodium loads and different sugar counts. They also get pulled into the same old health debates about teeth and bones, debates that usually cite research that never actually tested plain sparkling water.
A 2026 Purdue University study finally measured what happens in someone’s mouth after a real sip of the real product, not a stand in for it. The results settle more than one worry at once.
The short version
- Labels differ: seltzer has no added minerals, club soda adds about 75 mg of sodium per can, and tonic water carries about 32 grams of sugar.
- Teeth: in the Purdue study, plain and calcium fortified sparkling water never pushed mouth pH below the 5.5 enamel erosion threshold. Flavored seltzers with citric acid were not tested.
- Bones: the bone density link traces to cola’s phosphoric acid and caffeine, not carbonation.
- Hydration: sparkling water hydrates just as well as still water.
- Home carbonation: filter tap water first, since carbonating does not remove chlorine taste.
The four labels do not mean the same thing
Federal rules define some of these terms, and the differences show up on the sodium line of the nutrition label well before they show up in taste.
Seltzer and club soda
Seltzer is the plainest of the four. It starts as filtered water and gets injected with carbon dioxide gas, with no minerals added, which is why most seltzer brands list zero milligrams of sodium on the label.
Club soda starts the same way but does not stay plain. Manufacturers add potassium sulfate, sodium bicarbonate, and sodium chloride for flavor.
That combination puts roughly 75 milligrams of sodium into a 12 ounce can, about 3 percent of a day’s recommended intake. That is not a lot on its own, but it adds up if you are tracking sodium closely.
Sparkling water and sparkling mineral water
Sparkling water carries a stricter definition than either of those. Under FDA rule 21 CFR 165.110, a product labeled sparkling bottled water has to contain the same amount of carbon dioxide it had when it emerged from its source. That gas can occur naturally or get restored after treatment.
Sparkling mineral water goes a step further and has to meet the FDA’s mineral water standard too: at least 250 parts per million of total dissolved solids pulled from a protected underground source.
We cover that standard in full in our guide to what mineral water actually is.
Tonic water
Tonic water breaks the pattern entirely. It gets its bitterness from quinine, extracted from cinchona bark, and most brands sweeten that bitterness with real sugar, not a diet sweetener.
A 12 ounce serving carries about 124 calories and 32 grams of sugar, close to what a can of cola carries. Reaching for tonic water instead of soda does not accomplish what people assume it does.
Does carbonation actually wear down tooth enamel
Every dentist who has weighed in on this question starts from the same number, so it is worth knowing before anything else makes sense.
Tooth enamel begins to dissolve once the mouth’s pH drops below 5.5. That threshold is where the old sparkling water worry comes from, since carbonation forms a weak acid, carbonic acid, the moment carbon dioxide dissolves into water.
What the Purdue study measured
A team at Purdue University, led by graduate researcher Wajiha Zulfiqar, tested that worry directly and presented the results at the NUTRITION 2026 conference.
Twenty adults drank four different beverages while researchers tracked salivary pH in real time, rather than just measuring the drink’s acidity in a lab:
- Sugar sweetened soda: dropped mouth pH the most and kept it low at both the 2 minute and 20 minute marks.
- Plain sparkling water and calcium fortified sparkling water: caused only a brief dip in the first few minutes, then recovered close to baseline by the 20 minute mark. Neither pushed pH below the 5.5 erosion threshold at any point measured.
- Still water: the comparison baseline.
Where the study stops
That is a real result, but it comes with real limits:
- No flavored seltzers. The study did not test the lime, grapefruit, or black cherry seltzers that make up a large share of what people actually buy. Those typically add citric acid for taste, which lowers pH more than carbonation alone does.
- Preliminary findings. The results were presented at a conference rather than published in a peer reviewed journal.
- Small sample size. Twenty adults is a starting point, not a final word.
The reassurance applies to plain and mineral fortified sparkling water. It does not automatically extend to a can of black cherry seltzer.
The bone density warning points at the wrong ingredient
This particular claim has circulated for two decades, and most of that time it has been missing one detail that changes the whole picture.
A 2006 analysis of Framingham Osteoporosis Study data, run out of Tufts University and published in the American Journal of Clinical Nutrition, found that women who drank cola three or more times a week had measurably lower bone mineral density in the hip.
Other carbonated drinks in that same dataset showed no comparable effect. The researchers pointed to phosphoric acid and caffeine, both concentrated in cola specifically, as the likely mechanism, not the carbonation itself.
Plain sparkling water and seltzer contain neither phosphoric acid nor caffeine. No study since has tied carbonation on its own to lower bone density.
The bone warning that keeps getting repeated about sparkling water in general is really a warning about cola, mislabeled somewhere along the way and never corrected.
The same kind of mislabeling shows up around alkaline water claims, where a real chemistry detail gets stretched into a health claim the research never actually supported.
Hydration and sodium are the two questions actually worth asking
Set the bone and enamel debate aside for a moment. These two questions decide whether sparkling water fits an actual daily routine, not a hypothetical one.
Hydration
A beverage hydration index study comparing thirteen common drinks against still water found sparkling water hydrates just as effectively, with no meaningful difference in the fluid retained.
An earlier study reached the same conclusion testing carbonated and plain water side by side. The bubbles do not interfere with how the body absorbs the water around them.
Sodium
Sodium is the number actually worth checking, and it depends entirely on which of the four drinks is in the glass. Seltzer and true sparkling water run close to zero. Club soda runs closer to 75 milligrams per can.
If you are managing blood pressure, kidney disease, or heart failure on a sodium restricted diet, read the label rather than assume all four are interchangeable. The gap between them stops being trivial once a few cans a day are involved.
Carbonating tap water at home skips a step worth not skipping
Home carbonation machines pull water straight from the kitchen tap, and that detail matters more than the marketing admits.
A countertop carbonator adds carbon dioxide. It does not filter anything out first.
If the tap water going into the machine carries a chlorine taste, that taste rides straight through and comes out the other side in the sparkling water. Carbonating water does nothing to remove chlorine taste on its own.
Running the water through a carbon filter before it goes into the machine solves that. It is the same fix we recommend for anyone dealing with chlorine taste at the tap generally.
A basic carbon filter pitcher or faucet filter gets tap water to pure-tasting water in under a minute, cheaper than buying bottled sparkling water by the case.
For most healthy adults, plain sparkling water or seltzer is a reasonable stand in for soda. The research available right now does not support the old worries once carbonation gets separated from cola’s phosphoric acid, tonic water’s sugar, and a squeeze of added citrus.
If you are managing blood pressure, kidney disease, or active dental erosion, still check the sodium line on club soda and the sugar line on tonic water specifically. Those two numbers are the real thing worth watching, not the bubbles themselves.
Jay
Jay is a health and wellness enthusiast with expertise in water quality and nutrition. As a knowledgeable advocate for holistic well-being, Jay successfully manages Type 2 Diabetes through informed lifestyle choices. Committed to sharing reliable and authoritative insights, Jay combines firsthand experience with a passion for enhancing health."