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Distilled water is water that has been purified by boiling it into water vapor then condensing it back into liquid in a separate container. Impurities in the original water that do not boil below or near the boiling point of water remain in the original container.
In general, non-purified water could cause or interfere with chemical reactions as well as leave mineral deposits after boiling away. One method of removing impurities from water and other fluids is distillation.
For example, ions commonly found in tap water would drastically reduce lifespans of lead–acid batteries used in cars and trucks. These ions are not acceptable in automotive cooling systems because they corrode internal engine components and deplete typical antifreeze anti-corrosion additives. Pollution Prevention Fact Sheet Antifreeze Recycling & Disposal. Utah Department of Environmental Quality, US
Any non-volatile or mineral components in water are left behind when the water evaporates or boils away. Water escaping as steam, for example from a boiler of heating system or steam engine, leaves behind any dissolved materials leading to mineral deposits known as boiler scale.
Low-volume humidifiers such as cigar can use distilled water to avoid mineral deposits.
Certain biological applications require controlled impurities, especially in experiments. For example, distilling water to be added to an aquarium would remove known and unknown non-volatile contaminants. Living things require specific minerals; adding distilled water to an ecosystem, such as an aquarium, would reduce the concentration of these minerals. Fish and other living things that have evolved to survive in lakes and oceans should be expected to thrive at mineral ranges found in their original habitat.
Controlled impurities as well as equipment reliability are critically important in medical applications where, for example, distilled water is used in continuous positive airway pressure (CPAP) machines to humidify air for breathing. Distilled water will not leave contaminants behind when the humidifier in the CPAP machine evaporates the water.
It is also possible for brewers to blend distilled water with hard water to mimic the soft waters of Plzeň.
Another application was to increase the density of the air to assist early airplane jet engines during takeoff in 'hot and high' atmospheric conditions, as was used on the early Boeing 707. Down the Susquehanna to the Chesapeake by John H. Brubaker, Jack Brubaker – page 163
can be relatively simple to design and build, with very cheap materials.
Distilling water with commercial equipment will almost completely remove all dissolved minerals such as calcium, magnesium, sodium, fluoride, potassium, iron, and zinc leaving a TDS of <1PPM, and reduce its electrical conductivity to <2 μS/cm. Typical tap water has electrical conductivity in the range of 200–800 μS/cm. The pH of distilled water is always slightly lower than 7 (neutral) because distilled water will absorb small amounts of carbon dioxide gas from the atmosphere which forms traces of carbonic acid and lowers the pH of distilled water to around 5.8 pH (very weakly acidic).
Municipal water supplies almost always contain trace components at levels which are regulated to be safe for consumption. Some other components such as trace levels of aluminium may result from the treatment process. Fluoride and other ions are not removed through conventional water filter treatments. However, distillation eliminates most impurities.
Distilled water is also used for drinking water in arid seaside areas lacking sufficient freshwater, via desalination of seawater. (Chapter 12 of the World Health Organization report Nutrients in drinking-water)
Water filtration and distillation devices are becoming increasingly common in households. Municipal water supplies often have minerals added or have trace impurities at levels which are regulated to be safe for consumption. Much of these additional impurities, such as volatile organic compounds, fluoride, and an estimated >75,000 other chemical compounds are not removed through conventional filtration; however, distillation and reverse osmosis eliminate nearly all of these impurities.
The drinking of distilled water as a replacement for drinking water has been both advocated and discouraged for health reasons. Distilled water lacks minerals and ions, such as calcium, that play key roles in biological functions, such as in nervous system homeostasis, and are normally found in Drinking water. The lack of naturally occurring minerals in distilled water has raised some concerns. The Journal of General Internal Medicine published a study on the mineral contents of different waters available in the US. The study found that "drinking water sources available to North Americans may contain high levels of calcium, magnesium, and sodium and may provide clinically important portions of the recommended dietary intake of these minerals". It encouraged people to "check the mineral content of their drinking water, whether tap or bottled, and choose water most appropriate for their needs". Since distilled water is devoid of minerals, mineral intake through diet is needed to maintain good health.
The consumption of hard water (water with minerals) is associated with beneficial cardiovascular effects. As noted in the American Journal of Epidemiology, consumption of hard drinking water is negatively correlated with atherosclerotic heart disease.
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