Purified water is a common label on bottled water and in-home filtration systems, referring to water that has undergone extensive treatment to remove chemicals, contaminants, and dissolved solids. This rigorous process yields a product of high purity, which is attractive to consumers concerned about the quality of their tap water. Evaluating whether this highly processed water is the most beneficial choice for daily consumption requires understanding the trade-off between removing unwanted pollutants and removing beneficial substances.
Defining Purification Methods
Water becomes “purified” through processes engineered to drastically reduce its Total Dissolved Solids (TDS) content. TDS includes inorganic salts, organic matter, and other materials dissolved in the water, ranging from beneficial minerals to harmful contaminants. The two most common methods used to achieve this state are reverse osmosis (RO) and distillation.
Reverse Osmosis (RO) works by forcing water under high pressure through a semi-permeable membrane. This membrane allows water molecules to pass through while blocking up to 99.9% of dissolved solids, including ions, salts, and heavy metals. The result is water with an extremely low TDS measurement.
Distillation mimics the natural water cycle by heating the source water until it vaporizes into steam. As the water turns to steam, all non-volatile substances, such as minerals and salts, are left behind. The steam is then collected and cooled back into liquid water, producing a product that is exceptionally pure and mineral-free.
The Health Trade-Off: Safety vs. Mineral Content
The primary benefit of purified water is the assurance of safety, especially when the source water is questionable or known to contain pollutants. The removal of harmful contaminants like chlorine, lead, pesticides, and microbial pathogens makes purified water a reliable source of clean hydration. For individuals with compromised water infrastructure or those who are immunocompromised, this level of purity is a significant health advantage.
The downside of this aggressive purification is the loss of naturally occurring minerals, particularly calcium and magnesium. Water can contribute a meaningful percentage of the daily intake for these essential nutrients, which are important for bone health and cardiovascular function. Exclusive consumption of water devoid of these minerals shifts the entire burden of intake onto the diet.
Water with a very low TDS is considered hypotonic, meaning it has a lower concentration of solutes than the fluids in the body’s cells. When consumed, hypotonic water can lead to a shift in the body’s fluid balance as the body attempts to maintain osmotic equilibrium. This can increase the rate of urine output, potentially diminishing hydration efficiency and leading to a loss of essential electrolytes.
Practical Scenarios for Use and Avoidance
Purified water is recommended for applications where the absence of minerals is beneficial or necessary. For sensitive household appliances like steam irons, humidifiers, and CPAP machines, using purified or distilled water prevents the buildup of mineral scale, which can damage the equipment. Similarly, in medical and laboratory settings, highly purified water is required for procedures like sterilization or chemical testing to ensure accurate results.
For general daily hydration in healthy individuals, exclusive long-term consumption of purified water is advised against unless it has been remineralized. Many bottled water producers that use RO technology now add minerals back into the water for taste and health purposes. A more balanced daily choice is often filtered tap water, which reduces common contaminants while retaining natural minerals, or commercially available remineralized water.