Ionized water is water that has been processed through electrolysis to modify its chemical characteristics. This process separates the water into two streams: one alkaline and one acidic. The primary interest for consumers lies in the alkaline stream, where the molecular structure and composition have been intentionally altered. The core concern is how long these desirable properties remain stable once the water has been dispensed, which dictates the effective window for consumption.
The Defining Characteristics of Ionized Water
Ionization affects two main properties of water: the potential of hydrogen (pH) and the Oxidation-Reduction Potential (ORP). The pH scale measures the concentration of hydrogen ions, determining if a substance is acidic (below 7), neutral (7), or alkaline (above 7). Ionized drinking water is specifically sought for its elevated pH, which typically ranges from 8.5 to 9.5, signifying a higher concentration of hydroxide ions (\(\text{OH}^-\)) than regular tap water.
The second defining feature is a negative ORP, measured in millivolts (mV), which indicates the water’s propensity to act as a reducing agent. Standard tap water usually carries a positive ORP value. A negative ORP value suggests the water has a surplus of electrons available to donate, a property associated with antioxidant potential. For the consumer, the longevity of the ionized water’s benefits hinges entirely on the stability of this high pH and, more significantly, this negative ORP.
Factors Causing Rapid Property Loss
The delicate chemical balance achieved during the ionization process is immediately vulnerable to interaction with the environment. The most significant factor causing the rapid decay of alkaline properties is the absorption of atmospheric carbon dioxide (\(\text{CO}_2\)). When water is exposed to air, \(\text{CO}_2\) from the surrounding environment readily dissolves into the liquid.
Once dissolved, the carbon dioxide reacts with the water to form carbonic acid (\(\text{H}_2\text{CO}_3\)). This acid neutralizes the alkalinity, causing the elevated pH level to steadily drop back toward a neutral 7.0. Any exposure to air, such as leaving the water in an open glass or a partially filled container, accelerates this process.
Furthermore, the negative ORP is particularly sensitive to oxidation, which occurs when the water is exposed to oxygen in the air or to light. Heat also accelerates the degradation of both the pH balance and the antioxidant content. This means the water begins to revert to its original state almost instantly upon exiting the ionizer.
The Practical Shelf Life of Ionized Water
The two properties of ionized water—negative ORP and high pH—decay at distinctly different rates, which dictates the practical shelf life. The negative ORP, cited as the antioxidant benefit, is highly sensitive to air exposure and generally begins to diminish within minutes of being dispensed.
Under typical conditions, the negative ORP often disappears entirely within 12 to 24 hours, even when stored in a sealed container. Therefore, to gain the maximum antioxidant potential, the water should ideally be consumed immediately after ionization. Waiting more than a day means the water has likely lost the majority of its reducing potential.
The alkalinity, or high pH, is more stable than the negative ORP. If stored properly in an airtight container, the pH level may be maintained for several days, sometimes up to a week. However, improper storage, particularly exposure to air, can cause the pH to drop significantly within 48 to 72 hours due to the absorption of atmospheric \(\text{CO}_2\). While the water remains safe to drink after these properties are lost, it functions essentially as ordinary filtered water.
Acidic ionized water, which is sometimes used for cleaning or skin applications, is generally more stable than its alkaline counterpart. Its pH remains constant for longer periods. In shaded and sealed conditions, its properties have been observed to persist for a year, though exposure to light can cause other properties to become inert within a few days.
Maximizing Stability Through Proper Storage
To counteract the rapid decay caused by air, light, and heat, proper storage is necessary. The choice of container material plays a significant role in preserving the water’s properties. Glass containers are preferred because they are chemically inert and will not interact with the water’s alkaline nature.
Vacuum-sealed stainless steel bottles or food-grade plastics, such as those marked #1 PETE or #2 HDPE, are also effective options. Standard metal containers should be avoided, as the high alkalinity may react with certain metals, altering the water’s composition and taste.
The most effective strategy for slowing the loss of negative ORP is to eliminate air space within the container. Containers should be filled completely to the brim before being tightly sealed, which minimizes the water’s contact with oxygen and carbon dioxide. Storing the water in a cool, dark environment, such as a refrigerator, further slows down the chemical reactions that cause property degradation.