Alkaline water has a pH level above 7.0, typically ranging between 8.0 and 9.0, making it less acidic than standard tap or bottled water, which usually hovers around a neutral 7.0. While many people consume alkaline water for its potential health benefits, the state of alkalinity is not permanent. The question of how long alkaline water remains alkaline depends heavily on the storage method and the specific way the water was originally produced.
How Atmospheric Exposure Causes pH Degradation
The primary enemy of alkaline water is the air we breathe, specifically the carbon dioxide (CO2) it contains. When alkaline water is exposed to air, CO2 molecules readily dissolve into the liquid. Once dissolved, the CO2 reacts with water molecules (H2O), forming a weak acid known as carbonic acid (H2CO3). This chemical process shifts the water’s balance toward acidity. The carbonic acid then releases hydrogen ions (H+) into the water, and the presence of these positively charged ions lowers the pH value. This reaction continues until the water’s pH drops significantly, often moving back toward a neutral level. The rate of this degradation is directly proportional to the amount of surface area exposed to the air. A wide-mouth glass left on a counter will lose its alkalinity much faster than a tightly sealed bottle.
Practical Storage Guidelines and Timeframes
Commercially bottled alkaline water, when sealed and stored correctly, will maintain its pH for the longest duration. If kept in its original, unopened container and stored in a cool, dark location, the alkalinity can remain stable for up to one to two weeks. Once opened, it is best to consume the product within two to three days to retain the intended pH level.
Freshly produced alkaline water, such as that made by a home water ionizer, is even more sensitive to degradation. The beneficial antioxidant properties in this water can begin to diminish in as little as 18 to 24 hours. To slow degradation, the most effective strategy is to limit air exposure. Freshly ionized water should be stored in an airtight, sealed container, ideally made of glass or BPA-free plastic, to prevent the absorption of atmospheric CO2. When stored this way, the elevated pH can be maintained for up to 72 hours for optimal quality. Refrigeration also helps by slowing the chemical reaction between the water and dissolved gases, further extending the stability of the alkalinity.
Stability Differences: Ionized Versus Mineral Water
The method used to create the alkaline water fundamentally affects its long-term stability. There are two primary types of alkaline water: ionized and mineral-buffered. Ionized water is produced through electrolysis, which separates the water into acidic and alkaline streams. The alkalinity in ionized water is primarily due to the presence of unstable dissolved gases and hydroxyl ions (OH-). Because these components are highly reactive and temporary, the elevated pH in ionized water is not as robust. This type of water loses its alkalinity and its antioxidant potential, often measured by a negative Oxidation-Reduction Potential (ORP), much more quickly than its mineral counterpart.
In contrast, mineral-buffered alkaline water achieves its high pH through the presence of naturally occurring or added stable minerals, such as calcium and magnesium bicarbonates. These minerals act as chemical buffers, making them highly resistant to changes in pH. The mineral compounds are capable of neutralizing the carbonic acid formed from atmospheric CO2 without immediately losing their own alkaline properties. Consequently, alkaline water created with mineral buffers is significantly more stable and maintains its pH level for a longer duration under the same storage conditions.