Deionized (DI) water is a highly purified form of water used primarily in industrial and laboratory settings, where the presence of even trace minerals can interfere with sensitive processes. Its extreme purity has generated public concern regarding its safety for consumption. Understanding the nature of DI water and how the body handles its unique composition addresses questions about immediate cellular effects and long-term nutritional consequences.
Defining Deionized Water
Deionized water is defined by the near-total removal of mineral ions, such as calcium, magnesium, sodium, and chloride. This purification uses ion exchange, where water passes through specialized resins that capture charged mineral particles. The resins release hydrogen (H+) and hydroxyl (OH-) ions, which combine to form pure H2O. This process results in water with extremely low electrical conductivity, making it ideal for electronics manufacturing and laboratory work. While DI water is purer than standard distilled water in terms of ionic contaminants, the process does not reliably remove uncharged organic molecules, pathogens, or bacteria. This hyper-pure water is primarily technical and is not produced for potable use.
The Immediate Osmotic Effect on Cells
When deionized water is swallowed, the immediate physiological effect relates to the principle of osmosis within the digestive tract. Osmosis dictates that water moves from low solute concentration to higher solute concentration to equalize the solvent concentration. The cells lining the stomach and intestines are bathed in bodily fluids rich in dissolved salts and electrolytes. Because DI water contains virtually no solutes, it creates a steep concentration gradient when it contacts these cells. This causes water to rapidly move into the cells, which can cause temporary, slight swelling of the epithelial cells.
However, the stomach contains highly concentrated acid and food particles, which instantly mix with the ingested water. This mixing quickly introduces ions and solutes back into the DI water, neutralizing its osmotic effect before it reaches the bloodstream. Consequently, drinking a small volume of deionized water is harmless because the body rapidly buffers the osmotic difference.
Impact on Mineral Intake and Electrolyte Balance
The long-term effects of consuming deionized water are tied to its complete lack of dissolved minerals, which affects the body’s electrolyte balance. Chronic and exclusive consumption of mineral-lacking water can minimally contribute to deficiencies in essential elements like calcium and magnesium. While drinking water is a supplementary source of these nutrients, the long-term absence can be a factor, especially if the diet is poor.
More significantly, consuming large volumes of demineralized water can lead to increased elimination of electrolytes, including sodium, potassium, and chloride, through urine. The intestine must pull electrolytes from the body’s reserves to aid in the absorption of the pure water, which dilutes the body’s internal electrolyte balance. The World Health Organization (WHO) states that demineralized water is not considered ideal for drinking without further enrichment due to these potential health risks.
Non-Physiological Safety Concerns
Beyond the direct biological effects, deionized water presents safety concerns related to its chemical nature and storage. Because DI water is aggressively pure, it acts as a highly effective solvent, sometimes called “hungry water.” This powerful solvent readily attempts to dissolve and absorb any materials it contacts to regain ionic balance.
If DI water is stored in non-inert containers, such as certain plastics or metal piping, it can leach contaminants from the container material into the water. This leaching can introduce toxic metal compounds or other chemicals, making the water unsafe to drink due to external contamination rather than its initial purity. Furthermore, when exposed to air, DI water rapidly absorbs carbon dioxide, which forms a weak carbonic acid, slightly increasing its conductivity and acidity.