Non-carbonated water is simply water that contains no dissolved carbon dioxide gas. It’s what most people drink every day from the tap, a filter pitcher, or a standard bottle of water. You might also see it called “still water” or “flat water,” especially on restaurant menus or European bottle labels, where the distinction from sparkling water matters more.
The term exists mainly to differentiate from carbonated (sparkling) water, which has carbon dioxide dissolved into it under pressure. That dissolved gas is what creates bubbles, a slightly tangy taste, and a lower pH. Remove the gas, and you have non-carbonated water.
How It Differs From Sparkling Water
The core difference is carbon dioxide content. Carbonated water typically contains between 3 and 7 grams of dissolved CO₂ per liter. Non-carbonated water has essentially none. That single variable changes the taste, the mouthfeel, and the acidity of the water.
A study analyzing 73 brands of bottled still water found an average pH of 6.81, with a range spanning from about 5.0 to 9.6 depending on the brand and mineral content. By comparison, 32 brands of carbonated water averaged a pH of 5.46, with some dipping as low as 4.22. For context, pure water is neutral at pH 7, and tooth enamel begins to soften below a pH of roughly 5.5. So most still water sits comfortably in the neutral-to-slightly-acidic range, while a significant share of sparkling waters fall below that enamel-safety threshold.
Types of Non-Carbonated Water
Not all still water is the same. The FDA recognizes several distinct categories for bottled water, and most of them are non-carbonated by default.
- Purified water has been processed through distillation, reverse osmosis, or deionization to remove dissolved solids and contaminants. Most large bottled water brands start with municipal tap water and run it through these treatments. Labels may say “distilled water” or “reverse osmosis water” depending on the method used.
- Spring water comes from an underground formation where water naturally flows to the surface. It must be collected at the spring itself or from a borehole tapping the same underground source, and it retains whatever minerals were present at the point of emergence.
- Mineral water is natural water containing at least 250 parts per million of total dissolved solids, things like calcium, magnesium, and bicarbonate. No minerals can be added after the fact. The mineral profile must remain consistent from batch to batch.
- Artesian water comes from a well that taps a confined aquifer, an underground layer of rock or sand where water is trapped under natural pressure. The water level in an artesian well sits above the top of the aquifer.
- Well water is drawn from a hole drilled into the ground that taps an underground water source. It’s the broadest and simplest category.
Tap water, of course, is also non-carbonated. It’s treated by municipal systems and regulated by the EPA rather than the FDA, which governs bottled water.
Hydration Compared to Sparkling Water
Still and sparkling water hydrate you equally well. A randomized trial that developed a “beverage hydration index” to compare how different drinks affect hydration status found no meaningful difference between the two. Your body absorbs the water the same way regardless of whether CO₂ was dissolved in it.
Where the difference shows up is comfort. Carbonated water causes the stomach to hold food higher up in the digestive tract. One study found that when people drank carbonated water with a meal, the upper portion of the stomach retained significantly more of both solids and liquids compared to still water (74% vs. 56% for solids, 43% vs. 27% for liquids). Overall digestion speed was the same, but that temporary distension in the upper stomach is what creates the bloated, full feeling some people notice with sparkling water. Non-carbonated water doesn’t produce this effect.
Effects on Teeth
This is one area where non-carbonated water has a genuine advantage. Dissolving carbon dioxide in water creates carbonic acid, which lowers the pH and can soften tooth enamel over time. Research on home soda makers found that highly carbonated water produced measurably greater enamel surface changes than low-carbonation water, and both caused more softening than still water. Adding calcium to the carbonated water helped offset some of that damage, but didn’t eliminate it entirely.
Plain still water, with its near-neutral pH, poses no risk to enamel. About 93% of still water brands tested in one large analysis had a pH above the 5.5 threshold where enamel erosion begins. Only a single brand out of 73 fell below 5.2. For sparkling water, nearly a third of brands tested fell below that same 5.2 mark. If you sip water throughout the day, choosing still over sparkling is easier on your teeth.
When the Label Says “Still”
In the United States, bottled water doesn’t need to be labeled “non-carbonated” or “still” because the absence of carbonation is the default. If carbon dioxide has been added, the label will say so, usually as “sparkling” or “carbonated.” In Europe and in restaurants, you’re more likely to be asked to choose between still and sparkling, which is why the terminology feels more familiar in those settings.
Some naturally carbonated mineral waters exist, where CO₂ is present in the underground source. These are labeled “naturally sparkling.” If a bottle of mineral water doesn’t carry that label, it’s non-carbonated.