Is There CO2 in Drinking Water? An Overview

December 8, 2025 •

4 min read

Nearly all natural water sources, from groundwater to surface water, contain some level of dissolved carbon dioxide (CO2). This naturally occurring gas is a normal part of the water cycle and is responsible for the slight acidity found in most water supplies.

Quick Summary

Yes, CO2 is present in drinking water, originating from natural processes and atmospheric absorption. When dissolved, it forms carbonic acid, which lowers the water's pH. Levels vary in still and sparkling varieties, with minimal health risks for most people, but potential for issues like tooth enamel erosion with excessive consumption of acidic, flavored versions.

Key Points

Natural Sources: CO2 enters drinking water naturally when rainwater absorbs it from the atmosphere and from decaying organic matter in groundwater.
Carbonic Acid Formation: When CO2 dissolves in water, it forms a weak carbonic acid, which lowers the water's pH and makes it slightly acidic.
Still vs. Sparkling: Still drinking water has low levels of naturally occurring dissolved CO2, while sparkling water contains significantly higher levels of intentionally added CO2 for effervescence.
Health Effects: Plain carbonated water is generally safe and hydrating but can cause gas and bloating in some individuals. Excessive intake of more acidic, flavored sparkling water can potentially harm dental enamel.
Corrosion: High levels of dissolved CO2 can make water corrosive, which can lead to the deterioration of plumbing systems over time.
Removal Methods: CO2 can be removed from water through aeration (air stripping), boiling, or advanced ion-exchange processes.

Sources of CO2 in Your Water

Carbon dioxide in drinking water originates from several sources, both natural and artificial. The most common natural occurrence is when rainwater absorbs CO2 from the atmosphere as it falls. As this water seeps through the ground, it may absorb additional CO2 from decaying organic matter or react with certain mineral formations. In fact, deep groundwaters, like those from a well, can have significantly higher levels of dissolved CO2 than surface waters.

Artificial sources are primarily found in bottled water products. Sparkling waters, seltzers, and club sodas are intentionally infused with pressurized CO2 gas to create effervescence. This process is known as carbonation and creates the bubbles that are the main feature of these drinks.

The Chemistry: From CO2 to Carbonic Acid

When carbon dioxide gas (CO2) dissolves in water ($H_2O$), it undergoes a chemical reaction to form carbonic acid ($H_2CO_3$). This is a weak acid that readily dissociates, creating hydrogen ($H^+$) and bicarbonate ions ($HCO_3^−$). The presence of these hydrogen ions is what lowers the water's pH, making it slightly acidic. The chemical reaction is a dynamic equilibrium:

$CO_2(aq) + H_2O(l) ightleftharpoons H_2CO_3(aq) ightleftharpoons H^+(aq) + HCO_3^−(aq)$

In still water, this process occurs naturally through exposure to the atmosphere. However, the effect is far more pronounced in artificially carbonated beverages, where high pressure forces large amounts of CO2 into the solution. The more CO2 dissolved in the water, the more acidic it becomes, which is why plain sparkling water typically has a pH of 3 to 4, significantly lower than the neutral pH of 7 found in pure water.

Potential Effects of Dissolved CO2

For most people, drinking water with dissolved CO2 is completely safe. The human body naturally regulates its pH levels, so consuming carbonated beverages has a negligible effect on overall body chemistry. However, the presence of CO2 can cause some aesthetic and health-related issues, particularly with high levels or in specific circumstances.

Health and Digestive Impacts

Dental Health: The primary concern with carbonated water is its effect on tooth enamel. While plain sparkling water is less damaging than sugary soft drinks, its mild acidity can still erode enamel over time with repeated, excessive exposure. Flavored seltzers with added citric acid are more erosive.
Digestive Comfort: For some individuals, especially those with irritable bowel syndrome (IBS) or gastroesophageal reflux disease (GERD), the carbonation in sparkling water can cause bloating, gas, and stomach discomfort. The bubbles can also temporarily increase feelings of fullness.

Water Quality and Plumbing Issues

High levels of CO2 can also affect tap water systems and well water. When dissolved CO2 is present in high concentrations, the resulting carbonic acid can make the water corrosive. This acidic water can then corrode copper and galvanized plumbing systems over time, leading to potential pipe damage and the leaching of metals into the drinking water.

Methods for Removing CO2 from Water

For applications where CO2 removal is necessary, such as in high-purity industrial processes or to protect plumbing, several methods exist:

Aeration (Air Stripping): This involves bubbling air through the water in a controlled tower system, which encourages the dissolved CO2 to off-gas into the atmosphere. This is a common method for municipal and large-scale industrial water treatment.
Heating/Boiling: The solubility of CO2 in water decreases as temperature increases. Boiling water is an effective way to drive off dissolved gases, including CO2. However, the water must be protected from re-absorption as it cools.
Ion Exchange: In deionization systems, specialized resins can remove the ionic forms of CO2 (bicarbonate and carbonate). This is used for creating highly pure water but is not a common household method for tap water.

Still vs. Carbonated Water: A Comparison

To better understand the differences, here is a comparison of still water and carbonated water.


Feature	Still Water	Carbonated Water (Seltzer/Sparkling)
Source of CO2	Minimal, from equilibrium with atmospheric air.	High, from forced injection of CO2 gas.
CO2 Levels	Typically low (under 10 ppm).	High, resulting in pronounced effervescence.
pH Level	Neutral (around 7.0) in pure water; higher with buffering minerals.	Mildly acidic (3-4 pH) due to carbonic acid.
Hydration Efficacy	Hydrates the body efficiently and quickly.	Equally hydrating but may slow consumption due to feeling of fullness from bubbles.
Primary Concern	Potential contaminants depending on the source.	Dental enamel erosion (especially with added acid/sugar) and digestive discomfort.
Target Consumer	General daily hydration, quick intake.	Beverage alternative for those who enjoy fizz and flavor without sugary additives.

Conclusion

In summary, yes, there is CO2 in drinking water. It is a natural component of both still and sparkling water, playing a key role in water's natural chemistry by affecting its pH. For still water, CO2 is present in small, harmless amounts absorbed from the air and ground. In sparkling water, it's a deliberate additive that creates the bubbly texture and taste. While plain carbonated water is a healthy, hydrating alternative to sugary sodas, people sensitive to its acidity should be mindful of potential dental effects and digestive issues. In contrast, high levels of natural CO2 in well water can cause corrosivity concerns for plumbing. Understanding these nuances helps consumers make informed choices about the water they drink. For further reading, explore the relationship between CO2 and water pH here.

Frequently Asked Questions

Yes, dissolved CO2 in drinking water is generally considered safe. The human body is equipped to handle and expel excess CO2, so the small amounts found in still water and the larger amounts in sparkling water pose no harm to overall health for most people.

No, drinking plain carbonated water has not been shown to harm bone health. The myth likely stems from studies linking dark sodas containing phosphoric acid to lower bone density, an effect not observed with carbonated water.

Cloudy or milky-looking tap water is often caused by harmless, dissolved gases, including CO2, coming out of the solution due to a change in temperature or pressure. If you let the glass sit, the water will clear from the bottom up as the gas escapes.

Yes, the simplest way to remove CO2 from tap water is by boiling it. Allowing the water to sit in an open container will also cause the gas to dissipate over time, a process that can be accelerated by stirring.

In plain sparkling water, CO2 gives a refreshing, bubbly, and slightly tangy or prickly sensation. In still water, the low levels of naturally dissolved CO2 are generally imperceptible to taste.

Both still and plain sparkling water are excellent choices for hydration. The 'better' option depends on personal preference and health considerations. Still water is less acidic and may be easier to consume in large volumes, while sparkling water can offer a satisfying alternative to sugary sodas.

Yes, when high concentrations of CO2 dissolve in water, they form carbonic acid, which can make the water more corrosive. This can lead to the corrosion of metal plumbing components over time.