Deionized (DI) water is water that has been processed to have virtually all of its mineral ions removed. This purification method targets charged particles like sodium, calcium, chloride, and magnesium, resulting in water with extremely low conductivity and high purity. Because of this high purity, DI water is utilized heavily in industrial, laboratory, and manufacturing settings, where dissolved minerals could interfere with processes. The question for general consumers, however, is whether this highly purified water, which is not intended for drinking, is safe to ingest.
How Deionization Works
Deionization is a water purification method that relies on a chemical exchange process to strip the water of ionic impurities. This process differs from distillation and reverse osmosis. The core mechanism involves passing water through specialized resin beads, known as ion exchange resins.
These resins come in two types: cation resins, which exchange positively charged ions for hydrogen ions, and anion resins, which exchange negatively charged ions for hydroxyl ions. When the liberated hydrogen and hydroxyl ions combine, they form a pure water molecule. The resulting water has a total dissolved solids (TDS) concentration approaching zero, making it exceptionally pure from a mineral standpoint. This process is highly effective at reducing conductivity but does not reliably remove uncharged contaminants such as bacteria, viruses, or organic molecules.
Immediate Risks: Contamination and Leaching
A significant safety concern regarding DI water is its lack of inherent protection against biological contaminants. Municipal tap water contains residual disinfectants, such as chlorine, that inhibit bacterial growth within the distribution system. Deionization removes these residual disinfectants completely, leaving the pure water vulnerable to microbial growth if stored in non-sterile tanks or piping systems.
The purity of DI water also makes it an aggressive solvent, often described as “hungry water,” actively seeking to dissolve materials it contacts. This aggressive nature causes the water to leach trace amounts of materials from its storage containers, pipes, and fittings. For instance, DI water can quickly extract metals like lead or copper from plumbing, or plasticizers and other chemical compounds from plastic tanks, introducing toxic substances into the water. This leaching effect means that the water’s quality can rapidly decline after treatment, making it unsafe for consumption.
The Physiological Impact of Zero Mineral Content
The primary health risk associated with regular consumption of deionized water stems from its lack of dissolved minerals, which affects the body’s fluid balance. Human body fluids maintain a precise concentration of electrolytes like sodium, potassium, and chloride. When mineral-free water is ingested, the body attempts to balance the concentration difference through a process called osmosis.
This osmotic pressure gradient causes the mineral-free water to pull electrolytes and minerals out of the body’s tissues, including the cells lining the digestive tract. Continuous intake of water with low mineral content can disrupt the body’s water and mineral metabolism, potentially leading to an electrolyte imbalance. Symptoms of this imbalance can include fatigue, weakness, muscle cramps, and headaches, reflecting the depletion of essential minerals.
While a single glass of DI water is unlikely to cause severe damage, regular or exclusive consumption is strongly discouraged. The lack of minerals also contributes to a diuretic effect, increasing urine output and accelerating the loss of essential electrolytes. Studies suggest that drinking water with a total dissolved solids level below 50 mg/L may have negative effects on metabolism and mineral absorption.