Monday, February 23, 2009

Distillation Water Treatment

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. (Vis. 1)

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

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

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