Water distillation is a purification method that mimics the natural rain cycle to achieve extremely high water purity. It separates water from contaminants by leveraging the difference in boiling points between water and impurities. This physical process involves a phase change: liquid water is converted into vapor and then back into liquid. The resulting product is water nearly devoid of all dissolved solids and minerals.
The Mechanical Process of Water Distillation
The purification process begins by heating the source water in a boiling chamber, which requires a significant amount of energy. As the water reaches its boiling point of 212°F (100°C) at sea level, it transforms into steam, or water vapor. This vaporization is the mechanism that achieves separation, as most contaminants have a much higher boiling point than water and cannot turn into a gas.
The pure steam then rises, separating from the impurities left in the boiling chamber. This vapor is directed into a cooling chamber known as the condenser. Inside the condenser, the steam is rapidly cooled, often by circulating cool air or water around the coils.
As the water vapor loses thermal energy, it undergoes condensation and reverts back to its liquid state, becoming purified water. This newly formed liquid, called the distillate, is then collected in a separate, clean container. Some distillation units incorporate an activated carbon filter at the end of this process to capture any remaining volatile organic compounds that may have vaporized with the water.
Impurities That Distillation Effectively Removes
Distillation effectively removes non-volatile substances. This includes nearly all inorganic compounds, which remain in the boiling chamber as concentrated residue. Examples of these removed contaminants are hardness minerals like calcium and magnesium, salts, and heavy metals such as lead and mercury.
The intense heat used in the boiling stage also makes distillation an excellent method for eliminating biological threats. The sustained boiling effectively inactivates microorganisms, including bacteria, viruses, and protozoan cysts. This results in a product that is free from nearly all total dissolved solids (TDS), achieving a purity level of up to 99.5 percent.
Primary Applications of Distilled Water
The unique purity of distilled water makes it necessary for specific applications. In laboratory and medical settings, it is used for preparing chemical solutions, rinsing sensitive equipment, and sterilizing instruments like autoclaves, where mineral deposits could skew results or cause damage. Kidney dialysis machines also require ultra-pure water to filter waste from the blood.
Distilled water is also the preferred choice for many small household and industrial appliances. Using it in steam irons, CPAP machines, and humidifiers prevents the mineral buildup, or scaling, that can shorten the lifespan of the equipment and interfere with its operation. In the automotive field, its use in lead-acid batteries and cooling systems helps prevent corrosion and mineral deposits on metal components.
Distilled Water Compared to Other Purified Water
Distilled water is often confused with other types of purified water, but a key difference is the level of total dissolved solids (TDS). Water from standard carbon filtration systems, like pitcher filters, removes chlorine and improves taste but leaves most dissolved minerals intact. This filtered water still contains a significant level of TDS and is not considered highly purified.
Reverse osmosis (RO) is another common purification method that forces water through a very fine semi-permeable membrane. While RO effectively removes up to 99% of contaminants and most dissolved solids, it often retains some level of trace minerals, resulting in a low but measurable TDS. Distilled water, by contrast, is virtually mineral-free, making it less practical for everyday drinking due to its flat taste. The distillation process is also more energy-intensive and slower than RO, making RO a more cost-effective and convenient solution for high-volume home use.