Water distillation is a purification method that mimics the natural hydrologic cycle of evaporation and condensation to produce highly pure water. The fundamental process involves converting liquid water into steam and then cooling the steam back into a liquid state in a separate container. This technique is extremely effective at separating water molecules from many contaminants, achieving a very high degree of purity.
The Mechanism of Separation
The purification mechanism in distillation is based on the significant difference between the boiling point of water and most chemical contaminants. When the source water is heated to its boiling point of 100° Celsius (212° Fahrenheit), it changes state into steam. This steam is essentially pure water vapor, leaving behind substances that do not easily vaporize at that temperature.
The steam then travels into a cooling coil or condenser, where it releases its heat and transitions back into liquid water. This newly formed liquid, called the distillate, is collected separately from the original boiling chamber. The non-volatile chemicals and solid impurities remain concentrated in the residue left at the bottom of the heating vessel.
Contaminants Effectively Removed
Distillation excels at removing inorganic chemicals and heavy metals because these compounds have boiling points far exceeding that of water. Substances like lead, arsenic, mercury, and barium are non-volatile and cannot transition into the steam phase.
Inorganic minerals, often referred to as “hard water” elements, are also effectively eliminated by this process. Calcium, magnesium, sodium, and fluoride, along with nitrates and various salts, remain as solid residue. The high heat also successfully inactivates and removes biological contaminants, such as bacteria, viruses, and protozoan cysts, ensuring the resulting water is microbiologically safe. Distillation typically achieves a removal rate of 99.9% for total dissolved solids, including large, non-volatile organic molecules like certain pesticides and herbicides.
Compounds That Remain
The primary limitation of distillation is its reduced effectiveness against Volatile Organic Compounds (VOCs) and certain other chemicals with low boiling points. VOCs are organic chemicals that vaporize easily, sometimes at temperatures lower than or close to water’s boiling point. These compounds, which include industrial solvents like benzene, toluene, and trichloroethylene, may vaporize alongside the water vapor.
Once vaporized, these volatile chemicals are carried with the steam into the condenser and re-condense back into the purified water. A common example is trihalomethanes, which are disinfection byproducts often found in chlorinated municipal water supplies. To address this issue, modern water distillers frequently incorporate a final activated carbon filter to adsorb any remaining VOCs from the collected distillate.
The Impact of Distillation on Water’s Mineral Content
A direct consequence of distillation’s efficacy in removing dissolved solids is the removal of naturally occurring inorganic minerals. The process eliminates calcium, magnesium, and potassium, which contribute to water hardness and are often considered beneficial. The resulting product is known as demineralized or distilled water, which has a noticeably flat taste due to the lack of these dissolved solids.
While these minerals are important for the body’s function, the majority of a person’s daily mineral intake comes from food, not drinking water. For individuals consuming a balanced diet, the lack of minerals in distilled water is generally not considered a health risk. However, some studies suggest long-term, exclusive consumption of demineralized water without adequate dietary compensation could potentially lead to minor mineral imbalances.