Distillation and reverse osmosis (RO) are two common and effective methods for purifying water by removing contaminants and impurities. Both processes yield water significantly cleaner than standard tap water. The choice between distilled water and RO water depends entirely on the intended application, as neither is universally superior. Understanding the distinct processes and resulting chemical profiles is necessary to determine the ideal option for specific needs.
The Purification Method: Distillation
Distillation mimics the Earth’s natural hydrologic cycle of evaporation and condensation. The process begins by heating source water until it converts entirely into steam. Since most inorganic compounds, heavy metals, and minerals have higher boiling points than water, they are left behind as solid residue. The steam rises into a cooling chamber, condenses back into liquid, and is collected as distilled water. This heating process also effectively kills microbiological contaminants like bacteria and viruses, ensuring high purity.
The Purification Method: Reverse Osmosis
Reverse osmosis (RO) is a pressure-driven filtration method that forces water through a highly selective semi-permeable membrane. The system works by applying external pressure that is greater than the naturally occurring osmotic pressure of the water solution. This pressure differential causes only the smaller pure water molecules to pass through the membrane’s microscopic pores. A standard residential RO system is usually multi-staged, beginning with pre-filters like sediment and activated carbon filters. These initial stages remove larger particles, chlorine, and certain organic chemicals, which protects the delicate RO membrane. The membrane then acts as the final barrier, rejecting the majority of dissolved inorganic solids and other impurities that are subsequently flushed away in a separate wastewater stream.
Chemical Differences: Purity and Mineral Content
The fundamental difference between the two purification methods is reflected in the final water chemistry, particularly the Total Dissolved Solids (TDS) count. Distilled water is created by separating the water from all dissolved substances, resulting in a product with a TDS level that is virtually zero parts per million (ppm). This level of purity means distillation is particularly effective at removing non-volatile substances like salts, hardness minerals, and heavy metals such as lead and arsenic.
Reverse osmosis is highly effective, removing up to 99% of dissolved solids; however, it rarely achieves the absolute zero TDS of distilled water. While distillation is excellent for non-volatile contaminants, it can sometimes allow volatile organic compounds (VOCs) with low boiling points to vaporize along with the water and re-condense. Modern RO systems, thanks to their pre- and post-carbon filters, are often more effective at removing these specific VOCs than a simple distiller.
The presence of minerals is another defining factor, as distillation removes nearly everything, including beneficial minerals like calcium and magnesium. RO systems are designed to remove undesirable dissolved solids. However, some consumer models include a post-filter stage to reintroduce trace amounts of healthy minerals. This remineralization process balances the water’s pH and contributes to a more natural and palatable final product.
Deciding Factors for Use: Drinking, Appliances, and Equipment
For applications where preventing mineral buildup is the primary concern, distilled water is the superior choice. Its near-zero mineral content prevents the formation of scale, which can clog internal components and reduce equipment lifespan. Distilled water is the standard recommendation for use in humidifiers, steam irons, and car batteries.
For daily consumption, reverse osmosis water is generally the more popular option. The complete absence of minerals in distilled water gives it a flat taste that many find unappealing. RO water, especially when remineralized, retains a crisp, fresher taste that is more palatable for long-term daily intake.
The long-term consumption of highly demineralized water is a common public concern, favoring RO water for drinking. Although the body primarily gets necessary minerals from food, RO systems can retain or add back a balanced profile of minerals. Therefore, for consistent household use where both purity and taste are desired, a multi-stage RO system is often the most practical solution.