Units with volatile gas vents can remove some volatile organic chemicals as well. With distillation, water is evaporated, leaving impurities behind. The steam is then cooled and becomes distilled water. But the distillation process is slow and consumes a lot of energy, making it expensive. It also consumes large amounts of water if the coolant used in the distillation process is water.
Distilled water can corrode materials such as iron and copper in plumbing systems.
45G. Reverse osmosis removes inorganic minerals such as radium, sulfate, calcium, magnesium, potassium, nitrate, fluoride, boron, and phosphorous. Water is filtered through a membrane that has passages smaller than the contaminant molecules. In addition, reverse osmosis is slow and wasteful of water, and filter replacement is costly. Some microorganisms may be small enough to pass through the reverse osmosis membrane and colonize the holding tank. It will remove dissolved iron and manganese when they are present in low concentrations.