Boiling water does not make it distilled; it is only the first part of a two-step purification method. Distillation is a physical separation process that relies on a change of state, involving both evaporation and subsequent condensation, to remove contaminants. Simply boiling water and leaving it in the original container does not create a purified product.
What Boiling Water Actually Does
Raising water to its boiling point of 100°C (212°F) is an effective method for immediate disinfection. This thermal process successfully eliminates biological contaminants, including most bacteria, viruses, and other disease-causing microorganisms. The high temperature denatures the proteins and disrupts the cell structures of these pathogens, rendering the water microbiologically safe.
Boiling also causes dissolved gases, such as carbon dioxide and chlorine, to escape into the atmosphere, which can subtly change the flavor profile. However, non-volatile impurities present in the original water do not vaporize with the water molecules.
As the pure water converts to steam and leaves the vessel, the remaining water volume decreases. Substances like heavy minerals, salts, and metals are left behind, causing their concentration to increase in the residual liquid. The final product of simple boiling is water that is free of pathogens but chemically more concentrated with inorganic solids.
The Complete Process of Distillation
The actual distillation process requires a closed system to complete the separation of water molecules from impurities. It begins with heating the water to its boiling point, causing it to vaporize into steam. This evaporation stage leaves the vast majority of non-volatile contaminants, such as calcium, lead, and other salts, behind in the boiling chamber.
The second, and most distinguishing, step is condensation, where the purified steam is directed into a separate, cooled container. As the steam contacts the cooler surface, it changes back into liquid water, known as the distillate. This collected liquid is chemically separated from the substances that remained in the original vessel, resulting in exceptionally pure water.
A secondary consideration involves volatile organic compounds (VOCs), which have lower boiling points than water and may vaporize along with the steam. To prevent these compounds from re-contaminating the distillate, commercial distillers often incorporate a venting mechanism or a post-distillation carbon filter. The combination of evaporation and condensation achieves the high purity standard of distilled water.
Comparing Purity Levels and Uses
The key difference between the two types of water is their final chemical composition. Boiled water is considered microbiologically safe due to the destruction of pathogens, but it retains its original content of Total Dissolved Solids (TDS), which are often concentrated. This makes it suitable for emergency drinking and cooking, where biological safety is the primary concern.
In contrast, distilled water is characterized by an extremely low TDS count, meaning it is virtually free of minerals, salts, and other inorganic compounds. This high level of purity makes it the required standard for laboratory experiments, medical sterilization equipment, and manufacturing processes. Distilled water is used in household appliances like steam irons and humidifiers to prevent the mineral buildup and scaling that would occur with boiled or tap water.