Alkaline water has a potential hydrogen (pH) level higher than standard tap water, typically ranging between 8.0 and 9.0, compared to neutral water at 7.0. Consumer interest stems from the belief that this higher pH can help neutralize acidity in the body, leading to its popularity as a hydration choice. However, the alkaline property is not permanent and diminishes over time due to chemical and environmental factors. The stability of the elevated pH depends on the source of the alkalinity and the storage conditions.
The Origin of Alkaline Water
The stability of alkaline water depends entirely on how its higher pH is achieved. Naturally alkaline water flows over rocks, picking up dissolved alkaline minerals like calcium, magnesium, and bicarbonate compounds. These mineral-rich compounds act as strong chemical buffers, resisting changes in pH when exposed to acids. This mineral-based alkalinity is highly stable and can maintain its pH for months or even years when kept sealed.
A second, less stable type is alkaline ionized water, created artificially through electrolysis. A water ionizer separates the water into acidic and alkaline streams using an electrical charge. This process achieves a high pH but lacks the robust mineral buffers of naturally sourced water. The resulting alkalinity is chemically fragile and susceptible to rapid degradation upon exposure to air.
Environmental Factors That Reduce Alkalinity
The primary factor reducing alkalinity in stored water is the absorption of carbon dioxide (\(\text{CO}_2\)) from the surrounding air. When exposed to the atmosphere, \(\text{CO}_2\) dissolves into the liquid and reacts with water molecules to form carbonic acid (\(\text{H}_2\text{CO}_3\)). This weak acid neutralizes the alkaline compounds, such as hydroxide or bicarbonate ions, causing the water’s pH level to gradually drop toward a neutral 7.0. This process accelerates significantly in open containers where the surface area is directly exposed to the air.
The type of alkalinity dictates the speed of neutralization. Ionized alkaline water, lacking mineral buffering capacity, loses its properties quickly. If left in an open glass, the effective alkalinity can diminish within a few hours, and the pH may drop substantially within 12 to 24 hours. Commercially bottled alkaline water, which is often mineral-enhanced, remains stable for a much longer period—sometimes several months—as long as the seal is intact.
Temperature also affects the rate of chemical degradation. Warmer temperatures accelerate the chemical reactions leading to \(\text{CO}_2\) absorption and carbonic acid formation. Storing alkaline water in a warm environment speeds up the loss of its elevated pH compared to a cool, stable environment. Even under optimal conditions, the inherent instability of ionized water limits its effective shelf life to about one to two weeks before a noticeable pH drop occurs.
Maintaining pH Levels Through Proper Storage
Maximizing alkalinity requires minimizing exposure to degradation factors. The most effective strategy is using airtight containers to create a physical barrier against atmospheric \(\text{CO}_2\). Filling the container completely, leaving minimal airspace, further reduces the amount of trapped \(\text{CO}_2\) that can react with the water.
The choice of container material influences pH maintenance. Glass containers are recommended because they are non-porous and non-reactive, helping preserve the water’s properties, including its pH and Oxidation-Reduction Potential (ORP). High-quality, BPA-free plastic is an alternative, and specialized vacuum-sealed stainless-steel bottles are also effective at preserving the alkaline charge and pH.
Cool, dark storage conditions slow down chemical activity. Storing the water in a refrigerator or cool pantry inhibits the reactions that cause \(\text{CO}_2\) absorption and pH reduction. Avoiding direct exposure to sunlight or heat is important, as both hasten the loss of alkalinity.
For ionized water, the best practice is to consume it as soon as possible after production, ideally within a few hours, to benefit from the highest pH. While sealed mineral-based alkaline water can last for months, once opened, it should be consumed within a few days to a week to ensure the pH remains in the desired alkaline range.