Does Boiling Water Remove Alkalinity? The Surprising Chemistry Revealed

December 28, 2025 •

3 min read

While boiling is a common method for disinfecting water, it has a specific and nuanced effect on water's mineral content and alkalinity. Understanding this process requires looking beyond simple disinfection and into the underlying chemical reactions, especially how it impacts different types of water hardness.

Quick Summary

Boiling can remove temporary alkalinity caused by bicarbonates of calcium and magnesium, but it does not affect permanent alkalinity. The process involves decarbonation, causing minerals to precipitate and settle, while concentrating other non-volatile contaminants.

Key Points

Temporary Alkalinity Removed: Boiling only removes alkalinity caused by bicarbonates (temporary hardness), not sulfates or chlorides (permanent hardness).
Decarbonation Process: Heating drives off carbon dioxide, causing soluble bicarbonate minerals to precipitate as insoluble carbonates (limescale).
pH Increase: The removal of carbon dioxide, which forms carbonic acid, causes a slight increase in the water's pH.
Concentrates Contaminants: Boiling evaporates water but leaves non-volatile contaminants like nitrates and heavy metals behind, increasing their concentration.
Kills Pathogens: While altering alkalinity in specific ways, boiling's primary function is to disinfect water by killing microorganisms.
Not Complete Purification: Boiling does not produce distilled or completely pure water and is insufficient for removing all chemical contaminants.

The Core Chemistry: How Boiling Affects Water's Composition

Boiling is an accessible and effective method for killing pathogens in water, but its chemical impact is more complex. The key to understanding how boiling relates to alkalinity is the process of decarbonation, which primarily affects temporary water hardness and alkalinity.

The Science of Temporary Hardness and Alkalinity

Water hardness comes in two main forms: temporary and permanent.

Temporary Hardness: This is caused by dissolved bicarbonate minerals, specifically calcium bicarbonate ($Ca(HCO_3)_2$) and magnesium bicarbonate ($Mg(HCO_3)_2$).
Permanent Hardness: This is caused by dissolved minerals such as calcium sulfate ($CaSO_4$) and magnesium sulfate ($MgSO_4$).

Boiling water only removes temporary hardness. When water containing bicarbonates is heated, the following reaction occurs:

$Ca(HCO_3)_2 (aq) + heat → CaCO_3 (s) + H_2O (l) + CO_2 (g)$

In this process, heat drives off dissolved carbon dioxide ($CO_2$), causing the soluble calcium bicarbonate to convert into insoluble calcium carbonate ($CaCO_3$), or limescale. This precipitates out of the water and settles at the bottom of the pot or kettle, effectively removing both temporary hardness and the associated alkalinity.

What Happens to the pH?

Alkalinity is the water's capacity to neutralize acid and is influenced by bicarbonate and carbonate ions. Boiling can slightly increase the pH of water by driving off dissolved carbon dioxide. Carbon dioxide forms carbonic acid in water, which lowers the pH. By removing this acidic gas, the water's pH rises, making it slightly more alkaline. However, this pH change can be temporary and may return to normal upon cooling and exposure to the atmosphere. For more in-depth research on the effects of boiling and storage, a recent study by MDPI offers detailed findings on various water parameters.

Boiling vs. Other Methods for Reducing Alkalinity

Boiling is not the only way to alter water chemistry. Depending on the type of alkalinity present and the desired outcome, other methods may be more suitable. It is important to distinguish between removing alkalinity and simply killing bacteria.

Here are some of the key differences in water treatment methods:

Comparison Table: Methods for Water Treatment


Feature	Boiling	Distillation	Ion Exchange Softener	Reverse Osmosis (RO)	Acid Injection
Removes Temporary Alkalinity?	Yes, precipitates out	Yes, leaves minerals behind	Yes, replaces with sodium ions	Yes, removes all dissolved solids	Yes, neutralizes
Removes Permanent Alkalinity?	No	Yes	Yes, replaces with sodium ions	Yes	Yes, neutralizes
Removes Pathogens?	Yes	Yes	No	Yes	No
Removes Other Contaminants?	Concentrates non-volatile ones	Yes	May not remove all	Yes	No, focuses on pH/alkalinity
Suitability	Best for small batches and temporary hardness	Best for high-purity water, small scale	Best for whole-house treatment	Best for broad contaminant removal	Best for industrial or precise pH control

Does Boiling Water Address All Water Quality Concerns?

While boiling is useful, it has limitations, especially for tap water. It's crucial to understand what boiling can and cannot do before relying on it for complete water purification.

Pros of Boiling:

Kills Pathogens: Boiling for at least one minute is highly effective against bacteria, viruses, and parasites.
Removes Temporary Hardness: It can precipitate calcium and magnesium bicarbonates, which reduces temporary hardness.
Drives Off Volatile Gases: It removes volatile compounds like chlorine and dissolved carbon dioxide.

Cons of Boiling:

Concentrates Contaminants: Non-volatile chemicals like nitrates, lead, and other heavy metals remain in the water and become more concentrated as water evaporates.
Ineffective on Permanent Hardness: It does not remove permanent hardness caused by sulfates or chlorides.
Alters Taste: Removing dissolved gases can leave the water with a 'flat' taste.
High Energy Consumption: It can be inefficient for treating large quantities of water.

The Verdict on Boiling and Alkalinity

In conclusion, boiling water can remove alkalinity, but only the temporary type associated with bicarbonates. It is a specific chemical process that relies on decarbonation and precipitation, not a universal solution for all types of water chemistry issues. For comprehensive water treatment, especially against permanent hardness and other chemical contaminants, boiling is not sufficient and can even worsen the concentration of some harmful substances. Understanding your water's specific composition is key to choosing the correct treatment method.

Frequently Asked Questions

Boiling water generally increases its pH. This is because dissolved carbon dioxide is released during the heating process, and since carbon dioxide forms a weak acid in water, its removal makes the water less acidic and thus, more alkaline.

No. Boiled water is only considered 'softer' if it had temporary hardness caused by bicarbonates, which precipitate out. It does not remove permanent hardness from sulfates and chlorides, so it is not a complete softening solution.

Hardness refers to the concentration of multivalent metal ions, primarily calcium and magnesium. Alkalinity is the water's ability to neutralize acids, and is primarily caused by bicarbonate and carbonate ions. They often coexist but are not the same thing.

Boiling removes some minerals, specifically those associated with temporary hardness like calcium and magnesium bicarbonates, by causing them to precipitate as limescale. However, it concentrates other dissolved minerals, not removes them.

Boiled water tastes flat because the process of heating drives off dissolved gases, including oxygen and carbon dioxide, that contribute to its fresh taste. Aerating the water by pouring it between containers can help restore some of the taste.

Repeatedly boiling water is not advisable, as it can significantly increase the concentration of non-volatile contaminants and minerals in the remaining water. It is better to use fresh water for each boil.

Boiling is impractical and ineffective for treating the large volume of water in a swimming pool. Pool alkalinity is typically managed by adding acid to neutralize the bases and promote CO2 release, with careful chemical balancing.