Alkaline water is defined as water with a potential of hydrogen (\(\text{pH}\)) level typically above 7.5, often ranging between \(\text{pH}\) 8 and \(\text{pH}\) 9. This elevated alkalinity is achieved either through ionization or by the addition of alkaline minerals, such as bicarbonates and hydroxides of calcium and magnesium. Subjecting this specially prepared water to high temperatures introduces chemical and physical changes that alter its composition. Boiling fundamentally affects dissolved gases, mineral concentration, and the overall stability of the water’s alkaline state.
The Chemical Impact of Boiling on \(\text{pH}\) Levels
Boiling water initiates degassing, expelling dissolved gases from the liquid. The most significant gas affecting water \(\text{pH}\) is carbon dioxide (\(\text{CO}_2\)), which dissolves to form carbonic acid (\(\text{H}_2\text{CO}_3\)). Carbonic acid slightly lowers the \(\text{pH}\) of natural water. When alkaline water is boiled, the \(\text{CO}_2\) is driven out, removing this acid-forming component. This removal can cause the water’s \(\text{pH}\) to temporarily increase, making it slightly more alkaline immediately after boiling.
For ionized alkaline water, however, the chemical impact is more complex. Boiling reduces the water’s negative Oxidation-Reduction Potential (\(\text{ORP}\)), which is often promoted as its antioxidant value. Studies on electrolyzed water have shown that boiling can cause a measurable decrease in the \(\text{pH}\) level from its initial, unboiled state. This suggests that heat disrupts the ionic structures that contribute to the artificially high \(\text{pH}\) and antioxidant capacity of ionized water.
Mineral Concentration and Sediment Formation
Alkaline water often contains a higher concentration of dissolved inorganic salts, specifically “hardness minerals” like calcium and magnesium. These minerals are non-volatile, meaning they do not evaporate with the water vapor during boiling. Consequently, as the water boils away, the remaining liquid volume shrinks, but the total mass of dissolved minerals stays constant. This evaporation leads to a progressive increase in the concentration of these minerals in the residual water.
The physical consequence of this concentration is a chemical reaction that converts the soluble forms of these minerals into insoluble solids. Specifically, soluble calcium bicarbonate (\(\text{Ca}(\text{HCO}_3)_2\)) is converted by heat into insoluble calcium carbonate (\(\text{CaCO}_3\)). This reaction, known as thermal decomposition, is responsible for the formation of the visible white residue often seen on the interior of kettles and pots, commonly referred to as limescale or sediment.
The precipitation of calcium carbonate and magnesium hydroxide means that the compounds contributing to the water’s alkalinity are removed from the solution. This leaves behind a volume of water with a significantly altered mineral profile and a reduced buffering capacity compared to the original water.
Implications for Perceived Health Properties
Alkaline water is frequently marketed with claims related to improved hydration, the neutralization of body acidity, and antioxidant properties. The process of boiling directly impacts the chemical characteristics associated with these claims.
The primary component affected is the Oxidation-Reduction Potential, or \(\text{ORP}\), which is a measure of the water’s capacity to act as an antioxidant. Boiling is a highly energetic process that introduces heat, which can rapidly diminish the negative \(\text{ORP}\) value often found in ionized alkaline water. Research indicates that this antioxidant property is significantly decreased or eliminated entirely when the water is brought to a boiling temperature. This change undermines one of the key advertised health benefits of consuming the water in its original form.
Furthermore, the physical precipitation of alkaline minerals into limescale means that the mineral structure the consumer is seeking is no longer fully available in the solution. Although boiling serves the practical purpose of sterilization by killing pathogens, it fundamentally transforms the water’s intended chemical and ionic profile. The final boiled product is therefore a chemically different substance from the original alkaline water, which may negate the specific reasons for its purchase.