The process used to produce completely pure water is called distillation. Distillation involves boiling the water to create vapor and then condensing the vapor back into liquid form in a clean container, leaving behind impurities, minerals, and contaminants. This process results in highly pure water because solid contaminants remain in the boiling apparatus and do not evaporate with the water vapor. For even higher purity, double distillation (repeated distillation) can be used, especially in laboratory settings. Other advanced purification methods include reverse osmosis, deionization, and ultraviolet treatment, but distillation remains the fundamental process for producing completely pure water.