Drinking water is fundamental, and the search for “pure” water often leads to questions about demineralized water. The fear that this water could be deadly is based on a theoretical scientific understanding of how the human body works. While consuming massive amounts in a short timeframe could potentially cause a fatal imbalance, under normal circumstances, it will not kill you. The actual risks are not acute poisoning but rather long-term nutritional deficiencies and cellular stress from exclusive, sustained consumption.
Defining Demineralized Water
Demineralized water, sometimes called deionized or distilled water, has undergone processes to remove virtually all dissolved mineral salts and ions. This purification results in extremely low levels of Total Dissolved Solids (TDS), often measuring near zero parts per million (ppm). Typical tap water, by comparison, ranges from 100 to 500 ppm. The removed solids include common elements like calcium, magnesium, sodium, and potassium.
The creation of this highly purified water involves methods such as distillation, reverse osmosis (RO), or ion exchange. This ultra-pure water is primarily used in industrial, laboratory, and medical settings. For example, it is used for cleaning contact lenses or in pharmaceutical manufacturing, where the presence of ions could interfere with processes.
Physiological Effects of Pure Water
The theoretical danger of demineralized water lies in the principles of cell biology, specifically the process known as osmosis. Osmosis describes the movement of water across a semi-permeable cell membrane to balance the concentration of solutes on both sides. Human cells, including red blood cells, are suspended in a fluid that has a certain concentration of salts and electrolytes.
When a person drinks a large volume of demineralized water, it enters the bloodstream and creates a hypotonic environment, meaning the fluid outside the cells has a much lower solute concentration than the fluid inside them. To equalize this difference, water rushes into the body’s cells, causing them to swell. This cellular swelling, or lysis, is particularly dangerous for brain cells, leading to symptoms like headache, nausea, and confusion, which can progress to seizures and coma.
A simultaneous danger is the rapid dilution of the body’s essential electrolytes, primarily sodium, in the bloodstream, a condition known as hyponatremia. The pure water pulls sodium and other ions out of the body’s reserves and increases urine output, leading to a negative mineral balance. Severe, acute hyponatremia from massive water intake can cause brain swelling and death. This extreme outcome typically requires consuming many liters of water in a short period.
Real-World Safety and Consumption
The risk of death from demineralized water is confined to scenarios of acute water intoxication, which can happen with any type of water consumed in dangerous excess. For normal daily consumption, the primary concern is the long-term impact of lacking minerals. Tap water and most bottled waters contain measurable amounts of beneficial minerals like calcium and magnesium, which contribute to daily dietary intake.
The World Health Organization (WHO) notes that exclusive, long-term consumption of water with extremely low Total Dissolved Solids (TDS) may increase the risk of health problems. These risks include cardiovascular disease and bone density issues. Cooking with water stripped of minerals can also cause a significant loss of calcium and magnesium from vegetables, sometimes as high as 60%.
The lack of dissolved salts causes demineralized water to be aggressively corrosive. This means it tends to leach minerals from pipes and containers. This property can inadvertently increase the intake of potentially toxic metals if the water is stored or transported through old piping systems. Therefore, while a few glasses are harmless, it is not recommended as a primary, sustained source of hydration.