Alkaline water has a higher pH level than standard drinking water, typically ranging from 8.0 to 9.5. The pH scale measures acidity or basicity, with 7.0 being neutral and values above 7.0 indicating alkalinity. The question of how long alkaline water is “good for” is not about safety, as water does not expire, but how long it retains its elevated pH. Since the high pH is chemically unstable in an open environment, the longevity of alkaline water depends almost entirely on storage and exposure to air.
Why Alkaline Water Doesn’t Maintain pH Forever
The primary reason alkaline water loses its high pH over time is its interaction with the atmosphere, specifically through the absorption of carbon dioxide (\(\text{CO}_2\)). This interaction is a natural chemical process that begins the moment the water is exposed to air. When atmospheric \(\text{CO}_2\) dissolves into the water, it reacts with the water molecules to form a weak acid called carbonic acid (\(\text{H}_2\text{CO}_3\)). The formation of this carbonic acid introduces hydrogen ions (\(\text{H}^+\)) into the water, which directly lowers the pH. Continuous exposure to an acidic compound like carbonic acid causes the water to gradually return to a more neutral pH.
Shelf Life of Sealed Commercial Alkaline Water
Commercial alkaline water sold in sealed bottles generally has a long shelf life, often similar to that of regular bottled water, which can be up to two years. The water is not losing its alkaline properties significantly during this time because the tight seal prevents the entry of atmospheric carbon dioxide. The packaging acts as a barrier, effectively halting the chemical process that would otherwise lower the pH. The expiration date printed on these bottles is not a safety date for the water itself, but rather a quality date related to the packaging. Over extended periods, chemicals from the plastic bottle can potentially leach into the water, which is the primary reason manufacturers recommend a time limit.
Maximizing the Longevity of Opened or Homemade Water
Once a commercial bottle is opened or water is produced at home, the shelf life of the elevated pH drops dramatically. For freshly made or ionized alkaline water, the alkalinity begins to decrease significantly within 12 to 24 hours of exposure to air. This rapid change necessitates immediate consumption or careful storage to retain the water’s beneficial properties.
To slow the \(\text{CO}_2\) absorption, the water must be stored in an airtight container. Glass or high-quality, BPA-free plastic containers are preferred because they are less reactive and do not introduce foreign chemicals into the water. When filling the container, minimizing the air space between the water and the lid reduces the amount of \(\text{CO}_2\) available to dissolve, helping to preserve the high pH.
Storing the water in a cool, dark place, such as a refrigerator, is also recommended because heat and light can accelerate the degradation process. By following these strict storage protocols, opened or homemade alkaline water can maintain its elevated pH for up to 1 to 3 days, or in ideal, airtight conditions, possibly up to two weeks.