Deionized water is highly purified water that has undergone processes to remove mineral ions and dissolved salts. While it may seem like the purest water, it is not considered suitable for drinking. Its characteristics make it valuable for industrial and scientific applications, but also problematic for human consumption. Understanding these properties clarifies why it is best left for its intended uses.
Understanding Deionized Water
Deionized water, often referred to as DI water or demineralized water, is characterized by the near-complete absence of mineral ions, such as sodium and calcium. Regular tap water contains these dissolved ions. Deionized water production relies on a process called ion exchange.
During ion exchange, water passes through beds of specialized resins. These resins have charged functional groups that attract and bind to the undesirable ions in the water. Positively charged ions (cations) are exchanged for hydrogen ions (H+), and negatively charged ions (anions) are exchanged for hydroxyl ions (OH-). The hydrogen and hydroxyl ions then combine to form pure water (H2O). This process effectively removes most dissolved impurities, resulting in water with very low electrical conductivity.
Cellular Impact of Deionized Water
Drinking deionized water affects human cells, particularly through osmosis. Osmosis is the movement of water across a selectively permeable membrane, like a cell membrane, from an area of higher water concentration to an area of lower water concentration. This movement occurs to equalize the concentration of dissolved substances, or solutes, on both sides of the membrane.
Human cells, including red blood cells, contain a specific concentration of solutes, creating an internal osmotic balance. When deionized water, which has almost no dissolved solutes, enters the body, it is considered hypotonic relative to the body’s cells. This means the concentration of water molecules is significantly higher outside the cells than inside. Consequently, water rushes into the cells to dilute their internal solutes and achieve equilibrium. This influx of water causes cells to swell and can lead to their bursting, a process known as lysis, particularly harmful to delicate cells like red blood cells.
Mineral Depletion and Other Risks
Beyond cellular impact, consuming deionized water can lead to longer-term health concerns due to its “hungry” nature. Deionized water lacks mineral ions, making it highly reactive and aggressive as it seeks to regain equilibrium by dissolving ions from its surroundings. When consumed, this pure water can actively pull essential minerals, such as calcium and magnesium, from the body’s tissues and fluids as it passes through the digestive system. While water is not the sole source of these minerals, its regular intake contributes to daily mineral needs, and chronic consumption of deionized water could lead to mineral imbalances or deficiencies over time.
Deionized water’s aggressive nature also poses a risk of re-contamination. As it flows through pipes or is stored in containers, it can leach trace amounts of metals or other substances from the materials it contacts. For instance, deionized water can corrode piping materials, increasing the potential for contaminants to dissolve into the water before consumption. This means that even if initially pure, deionized water can pick up impurities from its environment.
Everyday Applications of Deionized Water
Despite its unsuitability for drinking, deionized water is important in many industries and scientific applications due to its high purity. In laboratory settings, its lack of ions prevents interference with chemical reactions and ensures accurate experimental results. It is also used for rinsing and cleaning laboratory glassware and instruments, preventing residue buildup that could affect subsequent analyses.
Industrially, deionized water is important for processes where even trace amounts of minerals could compromise product quality or damage equipment. It is used in electronics manufacturing, including semiconductors, to prevent contamination that could lead to device malfunction. The pharmaceutical and cosmetic industries also rely on deionized water to ensure the purity and safety of their products. It is also employed in automotive cooling systems, steam irons, and car washes to prevent mineral deposits and water spots, ensuring optimal performance.