Dissolved Gases in Drinking Water: Why Molecular Size Matters

Dissolved gases in drinking water include oxygen, carbon dioxide, chlorine, and sometimes hydrogen. These gases dissolve at a molecular level and can affect taste, chemistry, and measurable properties like ORP. Molecular size influences how easily gases dissolve, diffuse, and escape from water.

Water Is More Than Just H₂O

Pure water consists of hydrogen and oxygen atoms bonded together as H₂O. However, drinking water in real-world conditions almost always contains additional dissolved substances.

These may include:

• Minerals such as calcium and magnesium
• Trace elements
• Dissolved gases

Dissolved gases are often overlooked because they are invisible. Yet they can significantly influence taste, chemistry, and measurable properties like oxidation-reduction potential (ORP).

Understanding dissolved gases helps clarify many conversations around water quality and hydrogen-rich water.

What Are Dissolved Gases?

A dissolved gas is a gas that has mixed uniformly into a liquid at the molecular level.

Common dissolved gases in drinking water include:

• Oxygen (O₂)
• Carbon dioxide (CO₂)
• Chlorine (in treated municipal water)
• Hydrogen (H₂), when intentionally infused

These gases are not visible as bubbles when properly dissolved. Instead, they exist between water molecules in solution.

The amount of gas that dissolves depends on factors such as pressure, temperature, and molecular properties.

How Gases Dissolve in Water

Gas solubility follows basic physical chemistry principles.

In general:

• Higher pressure allows more gas to dissolve.
• Lower temperature increases gas solubility.
• Smaller molecules tend to diffuse more easily.

When you open a carbonated beverage, pressure drops and carbon dioxide escapes as bubbles. The same principle applies to other dissolved gases.

Hydrogen behaves similarly. When dissolved in water under pressure, it remains in solution temporarily. Once exposed to air, it gradually diffuses out.

Oxygen and Carbon Dioxide in Drinking Water

Oxygen is naturally present in many water sources. It dissolves from the atmosphere and through water movement in rivers and reservoirs.

Dissolved oxygen influences taste and freshness. Highly aerated water can taste crisp.

Carbon dioxide, on the other hand, forms carbonic acid when dissolved, which slightly lowers pH. This is why sparkling water tastes mildly acidic.

These gases are naturally occurring and part of normal water chemistry.

Chlorine as a Dissolved Gas

In municipal water systems, chlorine or chloramine is often added for disinfection.

Chlorine increases oxidation potential and helps prevent microbial contamination during distribution. The World Health Organization emphasises the importance of maintaining disinfectant residuals in public water systems to protect against pathogens.

While chlorine improves safety, it can affect taste and odour. Activated carbon filters are commonly used to reduce chlorine levels for this reason.

Molecular Size and Why It Matters

Hydrogen (H₂) is the smallest molecule in existence. It consists of just two hydrogen atoms bonded together.

Because of its small size:

• It diffuses rapidly.
• It can move through membranes more easily than larger molecules.
• It escapes from water relatively quickly once exposed to air.
• This small molecular size is central to research exploring hydrogen’s biological behaviour. Some studies suggest that molecular hydrogen may interact selectively with certain reactive oxygen species. This area of research remains ongoing.
  
  

However, small size also means hydrogen does not remain dissolved indefinitely. Storage conditions matter.

Dissolved Hydrogen in Water

When hydrogen gas is infused into purified water, it becomes a dissolved gas.

Unlike carbonation, hydrogen does not significantly change taste, smell, or appearance. Its presence is typically measured using specialised dissolved hydrogen meters rather than visual cues.

Hydrogen can influence measurable properties such as ORP, often shifting readings toward negative values due to its reducing potential.

Stability and Storage

Because hydrogen molecules are so small, they can escape from water over time, particularly if:

• The container is not sealed
• The temperature increases
• The surface area exposed to air is large

This is why hydrogen-rich water is typically consumed soon after generation.

It is also why container quality and sealing mechanisms are important in hydrogen water systems.

For more on how hydrogen water differs from regular water, see our science-based overview.

Do Dissolved Gases Affect Hydration?

From a hydration standpoint, the body primarily requires water and balanced electrolytes.

Dissolved gases do not significantly change the basic hydrating function of water. Once consumed, gases like oxygen and hydrogen are either absorbed, metabolised in specific contexts, or exhaled.

Hydration depends mainly on:

• Total fluid intake
• Kidney function
• Electrolyte regulation
• Climate and activity level

Dissolved gases influence chemical properties, but they are not substitutes for proper hydration habits.

If you would like a refresher on how the body manages fluid balance, our article on how hydration works in the body explains the process clearly.

Common Misconceptions

“Bubbles mean more hydrogen.”
Visible bubbles are not a reliable indicator of dissolved hydrogen concentration.

“Gas-free water is more natural.”
Most natural water contains dissolved oxygen and other gases. Completely gas-free water is rare outside laboratory settings.

“All dissolved gases are harmful.”
Many dissolved gases occur naturally and safely in drinking water. Context and concentration matter.

Why This Topic Matters

Understanding dissolved gases provides clarity in a space that can sometimes feel confusing.

Water quality discussions often focus on minerals and contaminants, but dissolved gases also influence chemistry and measurement tools like ORP.

Recognising that hydrogen is simply another dissolved gas — with unique molecular properties — helps bring balance to the conversation.

Hydrogen water should be understood within the broader context of water chemistry, not separated from it.

Final Thoughts

Dissolved gases are a normal and often overlooked component of drinking water. They influence taste, measurable chemistry, and, in the case of hydrogen, ongoing areas of scientific research.

Understanding how gases dissolve — and how molecular size affects stability — allows for a clearer, more grounded conversation about water quality and hydrogen technology.

Hydration remains simple at its core: clean water, consumed consistently.

Medical Disclaimer:
This article is for educational purposes only and does not provide medical advice. Hydrogen water and dissolved gas discussions are not intended to diagnose, treat, cure, or prevent any disease. Always consult a qualified healthcare professional for medical concerns.