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Distillation is one of the oldest methods of water treatment and is still in use today though not commonly as a home treatment method. It can effectively remove many contaminants from drinking water, including bacteria, inorganic and many organic compounds.
Note that home water treatment is considered only a temporary solution. The best solutions to a contaminated drinking water problem are to either end the practices causing the contamination or change water sources. Distillation is a process that relies on evaporation to purify water. Contaminated water is heated to form steam. Inorganic compounds and large non-volatile organic molecules do not evaporate with the water and are left behind. The steam then cools and condenses to form purified water.
Distillation is most effective in removing inorganic compounds such as metals (iron and lead) and nitrate; hardness (calcium and magnesium); and particulates from a contaminated water supply. The boiling process also kills microorganisms such as bacteria and some viruses. The effectiveness of distillation in removing organic compounds varies, depending on such chemical characteristics of the organic compound as solubility and boiling point. Organic compounds that boil at temperatures greater than the boiling point of water (some pesticides) can be effectively removed from the water. Organic compounds that boil at temperatures lower than the boiling point of water (ex., benzene and toluene) will be vaporized along with the water. If these harmful compounds are not removed prior to condensation, they will recontaminate the purified product.
Distillation Units
Distillation units or stills generally consist of a boiling chamber, where the water enters, is heated and vaporized; condensing coils or chamber, where the water is cooled and converted back to liquid water; and a storage tank for purified water. 
Distillation units are usually installed as point- of-use (POU) systems. They are generally placed at the kitchen faucet and used to purify water intended for (drinking and cooking purposes only. Stills vary in size, depending on the amount of purified water they produce. The production rate varies from 3 to 11 gallons per day. Home stills can be located on the counter or floor, or attached to the wall.
Models can be fully or partially automated, or manual. Some stills have columns or volatile gas vents to eliminate organic chemicals with boiling points lower than water, thus ensuring uncontaminated water.
Operation, Maintenance and Cost
As with all home water treatment systems, stills require some level of regular maintenance to keep the unit operating properly. Unevaporated pollutants remaining in the boiling chamber need to be regularly flushed to the septic or sewer system. Even with regular removal of the residual water that contains unevaporated pollutants, a calcium and magnesium, scale will collect at the bottom of the boiling chamber. This scale eventually needs to be removed, usually by hand scrubbing or by an application of acid.
Heating water to form steam requires energy. This means that operating costs for distillation units are generally higher than those of other forms of home water treatment. The distillation process also removes oxygen and some trace metals from water. Some people claim this leaves the water tasting flat.
This information comes from Michigan State University Extension bulletin WQ 22, Distillation for Home Water Treatment.
Source: MSU Extension
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