Deionized water, often referred to as DI water, is a form of highly purified water from which almost all mineral ions have been removed. This extreme lack of dissolved solids directly influences its sensory experience. When consumed, deionized water is frequently described as having a noticeably “flat” or “bland” profile, lacking the familiar crispness of tap or bottled water. This absence of flavor is sometimes accompanied by a slight metallic or even bitter sensation, which sets it apart from ordinary drinking water.
Defining Deionized Water and the Role of Ions
Deionized water is defined by the removal of ions, which are electrically charged atoms or molecules. These ions represent dissolved minerals and salts, such as calcium, magnesium, sodium, chloride, and sulfate, naturally present in water sources. For sensitive applications in laboratories and manufacturing, these charged impurities must be virtually eliminated. Deionization achieves this high purity using specialized materials called ion exchange resins.
The water is passed through a column containing a mixture of two types of resin beads: cation resin and anion resin. The cation exchange resin attracts and captures positively charged ions (cations) from the water, releasing a hydrogen ion (H+) in their place. Following this, the anion exchange resin captures the negatively charged ions (anions), releasing a hydroxide ion (OH-). These released H+ and OH- ions immediately combine to form a molecule of pure water (H2O), effectively replacing all the dissolved mineral salts with pure water. This process is highly efficient at removing charged particles, resulting in water with extremely low electrical conductivity suitable for industrial use.
The Unique Sensory Profile
The most significant characteristic of deionized water’s flavor is its striking emptiness, often perceived as “flat.” It lacks the complex mixture of dissolved solids that give ordinary water its characteristic taste. The flavor in tap or spring water comes from trace minerals like calcium and magnesium, which contribute subtle notes of sweetness or mouthfeel. Without these mineral ions, DI water has no inherent flavor to stimulate the taste receptors, leading to blandness.
Interestingly, some people report a distinct metallic or slightly bitter note when drinking deionized water. This taste is not from the water itself but results from the extreme purity making the water highly “aggressive” and reactive. The water may leach trace amounts of materials, such as metal ions from plumbing or a stainless steel bottle, which can then be tasted.
The Saliva Dilution Effect
Another explanation is a sensory effect where the pure water rapidly dilutes the saliva in the mouth. Since saliva contains a natural concentration of salts and minerals, the sudden dilution changes the chemical environment on the tongue. The brain interprets this change as a strange, sometimes metallic or tingly, flavor.
The flat flavor of deionized water stands in sharp contrast to the distinct tastes of other water types. Hard tap water, which contains high levels of calcium and magnesium, may have a noticeable chalky or mineral profile. The absence of charged particles also means the water feels different in the mouth, contributing to the overall unusual sensory experience.
Health and Consumption Considerations
While occasional consumption of deionized water is generally not dangerous, it is not recommended for long-term use as a primary source of hydration. The primary concern relates to osmolarity, which describes the concentration of solutes in a solution. Deionized water is hypotonic, meaning it has a much lower concentration of dissolved ions than the fluids inside the body’s cells.
If consumed in large quantities, this hypotonic water can create an osmotic imbalance, causing water to move into cells to equalize the solute concentration. This process can potentially cause cells to swell and affect the delicate balance of electrolytes within the body. Electrolytes, such as sodium and potassium, regulate nerve and muscle function, and DI water offers none of these necessary dietary components.
The highly reactive nature of deionized water means it readily dissolves substances it contacts, which can lead to contamination. If the water is not sourced and stored properly, it can leach toxic metal compounds from the pipes and containers it travels through. Drinking water is better sourced from mineralized options to maintain proper internal balance and mineral intake.