Distillation has been a mainstay in water treatment for thousands of years, being touted by Aristotle as an effective means of purification as far back as 350 B.C.E.
The process begins by heating water to the boiling point, causing it to vaporize and rise into a condenser. Here the water vapor cools and condenses so it can be collected and stored.
Distilled water has a variety of household applications. Car batteries are filled with distilled water because impurities or additives in the water would reduce the life and performance of the battery. Mineral ions in untreated water are also corrosive to internal engine components, so distilled water is highly recommended for use in automotive cooling systems.
A combined solution of propylene glycol and distilled water is used in cigar humidors to maintain a steady level of relative humidity and avoid cigar rotting or aging. Solar stills, in which the heat of the sun drives evaporation from humid soil, can be designed and built using household materials, although they produce a relatively minor amount of water.
Distillation has historically been used for desalination purposes to convert sea water into potable water. It is also an effective means of removing soluble minerals like calcium and magnesium, as well as harmful bacteria.
While it has become significantly cheaper and more efficient in modern times, distillation is still a relatively expensive method of water treatment due to the energy requirements in heating the water to the boiling point. Additionally, synthetic chemicals such as pesticides, herbicides, and chlorine have lower boiling points than water, and are not removed through distillation.