Carbonated water is made by dissolving carbon dioxide gas into plain water under pressure. When the gas dissolves, it creates the bubbles, fizz, and slight tang that distinguish sparkling water from still. The process happens naturally in certain geological springs and is replicated industrially on a massive scale, but the underlying chemistry is the same.
How CO2 Gets Into the Water
Carbon dioxide dissolves into water more readily under two conditions: high pressure and low temperature. This is why commercial carbonation plants chill water before injecting CO2 under pressure, then seal it immediately in bottles or cans. As long as the container stays sealed, the pressure inside keeps the gas dissolved. The moment you crack the cap, pressure drops and the dissolved CO2 begins escaping as bubbles.
The relationship between pressure and solubility is straightforward. More pressure forces more gas into the liquid. Less pressure lets it escape. This is also why a half-empty bottle of sparkling water goes flat faster: there’s more headspace above the liquid, which means less pressure holding the CO2 in solution. Temperature matters too. Cold water holds gas better than warm water, which is why a warm seltzer fizzes out almost immediately when opened while a cold one stays bubbly longer.
The Chemistry Behind the Fizz
When carbon dioxide dissolves in water, it doesn’t just sit there as a gas in liquid form. Some of it reacts with the water to form carbonic acid. This is a weak acid, but it’s enough to lower the pH of the water and give carbonated water its mildly tart taste. Carbonic acid then partially breaks apart into hydrogen ions and bicarbonate, which is the same compound found in baking soda.
This reaction is reversible. As CO2 escapes from an open bottle, the carbonic acid converts back into water and gas. That’s why flat sparkling water tastes different from freshly opened sparkling water: the acid is gone along with the bubbles.
Where the Bubbles Form
Once you open a bottle and release the pressure, the water becomes supersaturated, meaning it contains more dissolved CO2 than it can hold at normal atmospheric pressure. The excess gas needs to escape, but it can’t just appear as a bubble anywhere. Bubbles form at what scientists call nucleation sites: tiny imperfections, scratches, or particles on a surface where gas molecules can cluster together and grow into a visible bubble.
This is why you see streams of bubbles rising from specific spots on the inside of a glass rather than forming uniformly throughout the liquid. A rougher, more textured surface creates more nucleation sites and releases more bubbles. A perfectly smooth surface suppresses them. Research on surface properties has shown this effect can be dramatic. In one experiment, pouring carbonated liquid into a cup with a superhydrophilic (extremely water-attracting) surface caused about 34% of the liquid’s mass to overflow from excessive foaming, while a superhydrophobic (water-repelling) surface suppressed bubble formation almost entirely after the initial pour. This same principle explains the famous Mentos-and-soda eruption: the candy’s pitted, water-attracting surface provides an enormous number of nucleation sites all at once.
Why Carbonation Tingles on Your Tongue
The fizzy sensation you feel when drinking sparkling water isn’t just from bubbles popping. Your tongue actually tastes the carbon dioxide through a dedicated biological pathway. Sour-sensing taste cells on your tongue carry an enzyme on their outer surface that converts CO2 into bicarbonate and hydrogen ions, the same breakdown products of carbonic acid. Those hydrogen ions activate the sour-sensing cells, creating the sharp, slightly acidic “bite” that carbonation is known for.
This is why even flat carbonated water that still contains dissolved CO2 can taste slightly different from plain water. The sensation isn’t purely mechanical. It’s a chemical signal your taste system is built to detect. People who find carbonation unpleasant are likely more sensitive to this sour-cell activation, while those who love it have learned to associate that mild acidic sting with refreshment.
Natural vs. Artificial Carbonation
Most carbonated water on store shelves is made artificially by injecting CO2 into purified or filtered water. But naturally carbonated water exists too. In places like Soda Springs, Idaho, underground water flows through carbonate rock formations where it picks up CO2 from geological activity. The slightly acidic groundwater reacts with these rocks, releasing carbon dioxide that dissolves into the water under the natural pressure of being underground. When this water reaches the surface through a spring, it arrives already fizzy.
Naturally sparkling mineral waters from volcanic regions work similarly. Volcanic activity produces CO2 deep underground, and water passing through these zones absorbs the gas along with dissolved minerals like calcium, magnesium, and silica. This is what gives natural mineral waters their distinctive taste compared to artificially carbonated water, which starts as a blank slate.
Seltzer, Club Soda, and Mineral Water
All carbonated waters share the same basic formula of water plus CO2, but the differences come down to what else is in the bottle. Seltzer is the simplest version: plain water with added carbonation and nothing else. Club soda starts the same way but includes added minerals and salts like sodium bicarbonate and potassium sulfate, which give it a slightly different taste and mouthfeel. These additions make club soda a closer match to naturally sparkling mineral water, though mineral water gets its minerals from the source rather than from a factory.
Tonic water is the outlier. It contains quinine (originally used as a malaria treatment), sweeteners, and sometimes other flavorings. It has significant calories and sugar, unlike the others, and is really more of a soft drink than a water.
Effects on Teeth and Hydration
Because dissolved CO2 creates carbonic acid, carbonated water is more acidic than still water. A study analyzing 32 commercially available carbonated waters found that none had a pH above 6.8, and ten fell below 5.2, which is the critical threshold where tooth enamel begins to dissolve. That sounds concerning, but context matters. Plain carbonated water is far less acidic than sodas, fruit juices, or sports drinks, and you’d need prolonged, frequent exposure for it to cause meaningful enamel erosion. Flavored sparkling waters with added citric acid are more of a concern than plain versions.
On the hydration front, carbonated water performs identically to still water. A randomized trial developing a Beverage Hydration Index found no difference in hydration status between sparkling and flat water. The carbonation doesn’t interfere with absorption. The only practical difference is that the bubbles can make you feel fuller, which may cause you to drink less in situations where you need a high volume of fluid, like during intense exercise.