Distilled water is water purified to a high degree, primarily by removing the dissolved solids and minerals found in source water. The process is one of the oldest purification methods, designed to create a consistent product with minimal impurities. However, the uniformity of the final product is complex. The journey from source water to a sealed bottle involves variables that can introduce subtle differences, making understanding its production and handling key to determining if all distilled water is truly identical.
Defining Distilled Water: The Purity Process
Distillation is a water purification method that mimics the earth’s natural hydrological cycle of evaporation and condensation. The process involves heating untreated water until it vaporizes into steam, leaving behind non-volatile substances in the boiling chamber. The steam is then directed into a cooling chamber, where it condenses back into liquid water and is collected.
This process effectively removes nearly all inorganic compounds, such as mineral salts and heavy metals. It also inactivates biological contaminants like bacteria and viruses through the boiling stage. The resulting product is characterized by a very low Total Dissolved Solids (TDS) measurement, often as low as 1-2 parts per million (ppm).
Comparing Purity: Distilled Versus Other Treated Waters
While distillation provides a high baseline of purity, it is often confused with other methods that also produce highly treated water, such as Reverse Osmosis (RO) and Deionization (DI). These methods achieve purity through different mechanisms and target different types of contaminants, resulting in distinct chemical profiles.
Reverse Osmosis (RO)
Reverse Osmosis uses pressure to force water through a semipermeable membrane, which physically blocks up to 99% of dissolved solids, including most bacteria and viruses. However, RO water typically retains a higher level of ionic impurities and has greater conductivity than distilled water.
Deionization (DI)
Deionization specifically targets charged particles, or ions, using ion-exchange resins to replace mineral cations and anions with hydrogen and hydroxyl ions. DI water is exceptionally pure in terms of ionic content, often having higher electrical resistivity than distilled water. The limitation of deionization is that it does not effectively remove uncharged organic molecules or microorganisms, which is why it often requires pre-treatment with RO or filtration.
Distillation’s Unique Profile
Distilled water’s strength is its simultaneous removal of both non-volatile inorganic compounds and biological contaminants through the phase change. The final conductivity of distilled water is typically around 1 million ohm-centimeters (1 MΩ⋅cm) of resistivity, making it a consistent benchmark for pure water. While distillation is reliable, it is just one of several methods used to achieve different types of high-purity water, each with a unique chemical fingerprint.
Manufacturing and Storage: Factors Affecting Final Quality
Despite the highly consistent nature of the distillation process itself, the answer to whether all distilled water is the same is no, due to factors applied after condensation. One significant variable is the potential for contamination by Volatile Organic Compounds (VOCs), such as benzene or toluene, which have boiling points lower than water. These compounds can vaporize along with the water and re-condense in the final product if the distiller is not equipped with a post-distillation carbon filter.
Another major source of variation is the post-processing handling, which includes the quality of the equipment and storage. Water that has just been distilled is sterile, but it is highly susceptible to recontamination from piping, storage tanks, and spigots if they are not consistently sterilized. If a commercial distiller is idle for a period, bacteria can be reintroduced from the final outlet, allowing microbial growth during storage.
The container itself also introduces differences in final quality, as leaching from plastic or glass packaging can occur over time. Furthermore, water intended for laboratory or medical use often undergoes a second or third distillation (double or triple-distilled) and is subjected to stricter testing standards than commercially bottled drinking water. These different grades of handling and quality control mean that the final product sold to a consumer will not always test identically across all brands or batches.