Why Cold Water Tastes Better: The Science of Dissolved Oxygen and Why Steam Systems Remove It
- MTS DNC ENERGY CONSULTANTS LIMITED
- Jul 5
- 3 min read
Have you ever noticed that cold water usually tastes fresher than warm water? The answer lies in the amount of dissolved oxygen the water contains.
This same scientific principle is also one of the most important considerations in steam generation, boiler design, and industrial heating systems. While oxygen improves the taste of drinking water, it becomes one of the biggest causes of corrosion in steam systems.
In this article, we explain why temperature affects dissolved oxygen, how this changes the taste of water, and why oxygen removal is essential for boilers and steam applications.
💧 Why Does Cold Water Taste Better?
Fresh drinking water contains small amounts of dissolved oxygen (O₂) absorbed naturally from the atmosphere.
At lower temperatures, water molecules move more slowly, allowing more oxygen to dissolve and remain in the water.
The result is water that tastes:
Crisp
Fresh
More refreshing
This is one reason chilled water is generally preferred over warm water.
🌡️ What Happens When Water Is Heated?
As water temperature increases, its ability to hold dissolved oxygen decreases dramatically.
As the water warms:
Water molecules gain kinetic energy.
Oxygen molecules escape from the liquid.
Dissolved gases are released into the atmosphere.
By the time water reaches boiling point, almost all dissolved oxygen has been removed.
This is why previously boiled water often tastes "flat" compared with fresh cold water.
📊 Dissolved Oxygen at Different Temperatures
The table below shows the approximate amount of dissolved oxygen freshwater can hold at atmospheric pressure.
Water Temperature | Dissolved Oxygen |
0°C | 14.6 mg/L |
10°C | 11.3 mg/L |
20°C | 9.1 mg/L |
40°C | 6.3 mg/L |
60°C | 4.6 mg/L |
80°C | 2.8 mg/L |
90°C | ≈2.0–2.5 mg/L |
100°C (boiling) | ≈0 mg/L |
At 90°C, water typically contains only around 2 mg/L of dissolved oxygen—roughly 20–25% of what it can hold at room temperature.
⚙️ Why Is Oxygen Removed in Steam Systems?
Although oxygen makes drinking water taste better, it is highly undesirable inside boilers and steam systems.
When dissolved oxygen comes into contact with steel at elevated temperatures, it causes corrosion.
The basic chemical reaction is:
Iron + Oxygen + Water → Iron Oxide (Rust)
Even very small amounts of oxygen can cause:
Corrosion of boiler tubes
Pitting of steel pipework
Damage to valves and heat exchangers
Reduced equipment lifespan
Increased maintenance costs
Reduced steam quality
For this reason, boiler feedwater is carefully treated before entering the boiler.
🔥 How Is Oxygen Removed?
Modern steam systems typically remove oxygen using three methods.
1. Thermal Deaeration
Water is heated close to its boiling point (typically 102–105°C under pressure inside a deaerator).
Heating greatly reduces oxygen solubility, allowing dissolved gases to escape.
2. Mechanical Venting
The released oxygen and other non-condensable gases are safely vented to atmosphere.
3. Chemical Oxygen Scavengers
Small traces of oxygen are removed using specialist chemicals such as:
Sodium Sulfite (Na₂SO₃)
Carbohydrazide
DEHA (Diethylhydroxylamine)
These chemicals react with the remaining oxygen before it can attack the steel surfaces.
❓ Why Isn't Simply Boiling Water Enough?
Boiling removes most dissolved oxygen, but industrial steam systems continuously receive fresh make-up water containing new dissolved gases.
Therefore, modern boiler plants combine:
Thermal deaeration
Mechanical venting
Chemical treatment
Together, these methods can reduce dissolved oxygen to less than 0.005 mg/L (5 ppb)—far lower than the approximately 2 mg/L present in water at 90°C.
🏭 Why This Matters in Building Services Engineering
Understanding dissolved oxygen is important when designing:
Steam boiler systems
Heating plant rooms
Heat exchangers
Industrial process systems
Pharmaceutical facilities
Food production plants
District heating systems
Correct water treatment significantly extends equipment life, improves efficiency, and reduces maintenance costs.
At MTS DNC Energy Consultants and NEXUS M&E Design, we design mechanical systems that prioritise long-term performance, reliability, and energy efficiency through sound engineering principles and best practice.
✅ Key Takeaways
✔ Cold water contains more dissolved oxygen, giving it a fresher taste.
✔ As water temperature increases, its ability to hold oxygen decreases.
✔ At 90°C, water typically contains only about 2 mg/L of dissolved oxygen.
✔ Boiling removes almost all dissolved oxygen from water.
✔ Steam and boiler systems intentionally remove oxygen to prevent corrosion and extend equipment life.
✔ Modern boiler plants use thermal deaeration, mechanical venting, and chemical oxygen scavengers to achieve extremely low dissolved oxygen levels.
📍 Disclaimer
The content shared in these posts is intended for informational purposes only and should not be interpreted as design advice, specifications, or a calculation template. For professional guidance or design services, please contact us through our contact form.
