Carbon dioxide gas dissolved under pressure is what makes sparkling water fizzy. When water is sealed in a bottle or can with CO2 forced into it, the gas stays trapped in the liquid. The moment you crack the seal, that pressure drops, and the dissolved gas escapes as the bubbles you see and feel.
How CO2 Gets Into the Water
Carbonation works because of a basic principle: gas dissolves more easily in liquid under higher pressure. In a bottling plant, CO2 is pumped into chilled water at pressures well above what you’d find in the open air. The gas molecules squeeze into the spaces between water molecules and stay there, invisible and dissolved, as long as the container stays sealed. Commercial sparkling water typically contains around 5 grams of dissolved CO2 per liter.
Temperature matters too. Cold water holds onto CO2 much better than warm water. That’s why a warm bottle of sparkling water erupts more aggressively when opened, and why a cold one keeps its fizz longer in your glass. Manufacturers carbonate water at low temperatures to pack in as much gas as possible before sealing.
What Happens When You Open the Bottle
The hiss you hear when you twist off a cap is pressurized CO2 escaping from the headspace above the liquid. With that pressure gone, the water is suddenly holding more dissolved gas than it can maintain at normal atmospheric pressure. It becomes supersaturated, and the CO2 starts leaving the liquid as bubbles.
Those bubbles don’t just appear anywhere, though. Spontaneous bubble formation in the middle of still liquid is essentially impossible from a physics standpoint. Bubbles need a starting point: tiny imperfections, scratches, or trapped air pockets on the surface of your glass, the walls of the bottle, or even microscopic fibers from a cloth. Scientists call these nucleation sites. Each little scratch or fiber acts as a launchpad where CO2 molecules gather, form a bubble, and grow until the bubble is buoyant enough to detach and float to the surface. That’s why you often see steady streams of bubbles rising from the same spot on the side of a glass.
Pouring also releases a burst of fizz. The turbulence of liquid splashing into a glass creates a cloud of bubbles all at once, which is why a freshly poured glass looks so lively compared to one that’s been sitting.
The Chemistry Behind the Tingle
Fizz isn’t just about bubbles. A small portion of the dissolved CO2 reacts with the water itself to form carbonic acid. This reaction is what gives sparkling water its slightly tart, acidic bite. Plain sparkling water typically has a pH between about 4.9 and 5.3, noticeably more acidic than still water, which sits closer to 7. S. Pellegrino, for example, measures around 4.96, while Perrier comes in at about 5.25.
That carbonic acid is also responsible for the tingling sensation on your tongue. Your mouth contains an enzyme called carbonic anhydrase that speeds up the conversion of CO2 into carbonic acid right inside your cells. The resulting drop in pH activates pain-sensing nerve receptors called TRPA1, which register the prickly, stinging feeling. Swedish scientists first demonstrated this connection in the 1960s by giving people a drug that blocks carbonic anhydrase. With the enzyme disabled, the tingle from carbonated water virtually disappeared.
Separately, the acidity triggers sour taste receptor cells on your tongue. So carbonation is really a two-part sensory experience: a physical tingle from nerve activation and a mild sour taste from acid detection. The bubbles bursting on the surface add a tactile element, but the signature “bite” of sparkling water is chemical, not mechanical.
Natural vs. Artificial Carbonation
Most sparkling water on store shelves is artificially carbonated, meaning CO2 is mechanically injected into still water. But some mineral waters emerge from the ground already fizzy. In volcanic and geologically active regions, underground water picks up CO2 from two main sources: the slow dissolution of carbonate rock layers (like limestone) deep below the surface, and direct release of gas from magma or mantle plumes. In parts of eastern Belgium, for instance, naturally carbonated springs draw their CO2 from carbonate rocks sitting 2 to 6 kilometers underground, combined with gas escaping from deep volcanic reservoirs.
The end result is the same, dissolved CO2 under natural geological pressure, but naturally sparkling mineral waters also pick up minerals along the way that affect flavor. That’s what distinguishes them from seltzer, which is just plain water with added CO2 and nothing else.
Seltzer, Club Soda, and Sparkling Mineral Water
All three are carbonated water, but the differences come down to what else is in the bottle. Seltzer is the simplest: water plus CO2, with no added minerals. Club soda starts the same way but includes salts like potassium sulfate and sodium citrate, giving it a slightly mineral, almost earthy taste designed to mimic natural mineral water. Sparkling mineral water comes from a natural spring and contains whatever minerals were present in the source, sometimes with additional CO2 added to boost the fizz.
Does the Acidity Harm Your Teeth?
Because carbonation creates carbonic acid, people reasonably wonder whether sparkling water erodes tooth enamel. The research paints a nuanced picture. Lab studies have shown that enamel exposed to carbonated water does show more surface erosion than enamel exposed to plain still water. However, plain sparkling water is far less acidic than sodas, citrus juices, or sports drinks, which can have pH values as low as 2 to 3. The pH of unflavored sparkling water hovers around 5, which is mild by comparison.
Flavored sparkling waters can be a different story, since added citric acid or other flavorings push the pH lower. If you’re drinking plain carbonated water, the erosive potential is minimal compared to virtually any other acidic beverage. The biggest risk factors for enamel erosion remain sugary sodas, fruit juices, and drinks with added acids.