The Surprising Truth: Boiling Doesn't Remove Most Magnesium
Contrary to popular belief, simply boiling water does not effectively remove the majority of magnesium from it. Magnesium is a non-volatile mineral, meaning it does not evaporate with the water when heated. The boiling process is effective for killing microorganisms like bacteria and viruses, which is why it is often used for disinfection, but it does little to address dissolved inorganic substances. In fact, by evaporating a portion of the water, the concentration of all remaining dissolved minerals—including magnesium—actually increases. The change in magnesium levels depends entirely on the type of magnesium compound present in the water.
Understanding Water Hardness and The Role of Boiling
Water hardness is determined by the concentration of dissolved polyvalent metallic ions, primarily calcium and magnesium. The effect of boiling is different for the two types of water hardness:
Temporary Hardness: What Boiling Can Affect
Temporary hardness is caused by the presence of dissolved bicarbonate minerals, such as magnesium bicarbonate ($Mg(HCO_3)_2$). When you boil water containing these compounds, a chemical reaction occurs that drives off carbon dioxide ($CO_2$), leading to the precipitation of insoluble magnesium carbonate ($MgCO_3$) or magnesium hydroxide ($Mg(OH)_2$). This insoluble solid then settles at the bottom of the pot or kettle, forming what is commonly known as limescale or kettle fur. By converting some of the soluble magnesium into an insoluble solid, boiling effectively reduces the temporary hardness of the water.
$Mg(HCO_3)_2(aq) \rightarrow MgCO_3(s) + H_2O(l) + CO_2(g)$
Permanent Hardness: What Boiling Cannot Affect
Permanent hardness is caused by salts that are more stable and do not precipitate when heated, such as magnesium sulfate ($MgSO_4$) and magnesium chloride ($MgCl_2$). These salts remain dissolved in the water even after prolonged boiling. For this reason, boiling alone is not a comprehensive solution for softening all types of hard water. In water with high levels of permanent hardness, the magnesium content will not be reduced by boiling and will instead become more concentrated as the water volume decreases due to evaporation.
More Effective Methods for Removing Magnesium
For those who need to fully remove magnesium, perhaps due to sensitive machinery or for certain chemical processes, alternative methods are required that go beyond simple boiling. These include:
- Distillation: This process involves boiling the water and then collecting the steam, which is pure water vapor without the dissolved minerals. The steam is then condensed back into a liquid, resulting in purified, mineral-free water.
- Reverse Osmosis (RO): A filtration process that forces water through a semipermeable membrane. This membrane allows water molecules to pass through while trapping most dissolved salts, including magnesium.
- Ion Exchange: Used in water softeners, this method swaps out the magnesium and calcium ions with sodium ions, effectively softening the water.
- Chemical Treatment: Certain chemicals, like washing soda, can be used to precipitate out hardness-causing minerals.
Boiling vs. Advanced Water Treatment: A Comparison
| Feature | Boiling | Ion Exchange Softening | Reverse Osmosis | Distillation |
|---|---|---|---|---|
| Removes Magnesium? | Only precipitates some bicarbonate compounds, leaves others | Replaces most magnesium ions with sodium ions | Highly effective, removes nearly all dissolved minerals | Highly effective, removes nearly all dissolved minerals |
| Kills Pathogens? | Yes, effectively kills most microbes | No, does not disinfect water | No, does not disinfect water | Yes, effectively kills most microbes |
| Concentrates Minerals? | Yes, remaining minerals become more concentrated | No | No | No, separates minerals out completely |
| Creates Limescale? | Yes, precipitates cause limescale buildup | No | No | No |
The Takeaway: How to Approach Boiling and Magnesium
For most people, a small amount of magnesium from drinking water is not a health concern and can even contribute to daily intake. However, if you are concerned about water hardness due to taste, mineral deposits in appliances, or for specific health reasons, relying on boiling is only a partial solution. It can reduce temporary hardness, but it is not a substitute for a comprehensive filtration system designed to remove a broader spectrum of impurities. For pure, mineral-free water, distillation or reverse osmosis are far more effective methods than just bringing water to a boil. Always consider the specific water quality issue you are addressing before choosing a treatment method.
Conclusion
In summary, the notion that boiling water removes magnesium is only partially true for the magnesium compounds that cause temporary hardness. The majority of dissolved magnesium, especially from sulfates and chlorides, remains in the water, becoming even more concentrated as some water evaporates. For reliable and thorough magnesium removal, alternative methods like distillation, reverse osmosis, or ion exchange water softeners are necessary. Boiling is an excellent way to sanitize water from biological contaminants but should not be considered a mineral removal technique. For more information on water treatment, you can visit the Centers for Disease Control and Prevention website.
