What Happens to Mineral Water When You Boil It?
When you bring mineral water to a boil, you trigger several physical and chemical changes that are distinct from boiling standard tap water due to the presence of dissolved minerals. The primary goal of boiling water is to kill harmful microorganisms like bacteria and viruses, a process unnecessary for commercially bottled water, which is already microbiologically pure. The real effects of boiling are on the water's mineral content, taste, and potential contaminants.
Concentration of Minerals
As mineral water boils, pure water evaporates as steam, but the inorganic minerals and salts, such as calcium, magnesium, and sodium, remain behind. This causes the remaining water to have a higher concentration of these minerals. The effect is typically minimal with a single boil but becomes more pronounced if the water is repeatedly boiled or if a significant amount evaporates. High concentrations of minerals can lead to scale buildup (limescale) in kettles and pots, which is the same chalky residue found in regions with hard tap water.
Alteration of Taste and Texture
Boiling also drives off dissolved gases, primarily oxygen and carbon dioxide, which gives water its fresh taste. The loss of these gases results in boiled water having a flatter, less refreshing taste. For mineral water, this can diminish the specific flavor profile that comes from its unique mineral balance. Pouring the water back and forth between two clean containers after it has cooled can help re-aerate it and improve the taste.
Potential for Chemical Concentration
This is one of the more serious, though less common, concerns when boiling mineral water. If the source water contained any non-volatile chemical contaminants like nitrates, heavy metals (e.g., lead or arsenic), or pesticides, the process of evaporation would concentrate these substances in the remaining water. For regulated, high-quality bottled mineral water, this risk is very low. However, for well water or other untreated sources high in chemicals, boiling is ineffective and potentially dangerous, as it would only increase the concentration of these harmful compounds.
Impact on Water for Specific Uses
For Baby Formula
While some guidelines suggest boiling water for infant formula, using bottled mineral water is not recommended for this purpose, especially for newborns. The high concentration of minerals, particularly sodium and sulfates, can be difficult for an infant's developing kidneys to process. It is safer to use tap water that has been tested for safety, or a different type of commercially bottled water explicitly designated for infant use.
For Coffee and Tea
Boiling mineral water can significantly affect the flavor of hot beverages. Coffee experts often favor water with a specific mineral composition to achieve optimal flavor extraction. Excessive hardness from concentrated minerals can mute acidity in coffee, leading to a duller, more bitter taste. For those particular about the taste of their coffee, using filtered tap water or specially formulated water is often preferable to boiling mineral water.
Comparison: Boiling Mineral Water vs. Tap Water
| Feature | Boiling Mineral Water | Boiling Tap Water |
|---|---|---|
| Disinfection | Unnecessary, as it's already microbiologically pure. | Necessary for potentially contaminated sources to kill pathogens. |
| Mineral Content | Naturally high mineral content becomes more concentrated during boiling. | Mineral content depends on local source; can become more concentrated. |
| Taste | Altered; becomes flatter due to the loss of dissolved gases. | Altered; often loses some of its chlorine taste but can taste flat. |
| Chemical Contaminants | Concentrates existing non-volatile chemicals if present, though typically low in commercial products. | Concentrates heavy metals, nitrates, and other non-volatile chemicals if present. |
| Scale Build-up | High potential for scale, especially with hard mineral water. | Varies based on local water hardness; can cause scale. |
| Purpose | Primarily for making hot beverages or cooking, not for purification. | For disinfection during boil advisories or when using untreated water. |
Conclusion
While boiling mineral water is not inherently harmful from a microbiological standpoint, it is a largely unnecessary practice with several potential downsides. The process can change the water's taste and increase mineral concentration, potentially affecting the flavor of beverages and causing scale buildup. For some applications, like preparing infant formula, it is strongly discouraged due to the risk of excessive mineral content. Ultimately, the quality and safety of packaged mineral water are already assured, making boiling a redundant and sometimes counterproductive step. For safe drinking water, it is best to rely on a trusted source, whether bottled or appropriately filtered tap water. For more information on water safety and quality, the Centers for Disease Control and Prevention offers comprehensive guidance on making water safe in an emergency.
