Distilled water

Distilled water is water that has virtually all of its impurities removed through distillation. Distillation involves boiling the water and re-condensing the steam into a clean container, leaving most if not all solid contaminants behind.

Applications
In chemical and biological laboratories, as well as industry, cheaper alternatives such as deionized water are preferred over distilled water. However, if these alternatives are not sufficiently pure, distilled water is used. Where exceptionally high purity water is required, double distilled water is used.

Distilled water is also commonly used to top up lead acid batteries used in cars and trucks. The presence of other ions commonly found in tap water will cause a drastic reduction in an automobile's battery lifespan.

Distilled water is preferable to tap water for use in automotive cooling systems. The minerals and ions typically found in tap water can be corrosive to internal engine components, and can cause a more rapid depletion of the anti-corrosion additives found in most antifreeze formulations.

Using distilled water in steam irons for pressing clothes can help reduce mineral build-up and make the iron last longer. However, many iron manufacturers say that distilled water is no longer necessary in their irons.

Some people use distilled water for household aquariums because it lacks the chemicals found in tap water supplies. It is important to supplement distilled water when using it for fishkeeping; it is too pure to sustain proper chemistry to support an aquarium ecosystem.

Distilled water is also an essential component for use in cigar humidors. Mineral build-up resulting from the use of tap water (including bottled water, such as Dasani or Aquafina) will reduce the effectiveness of the humidor.

Drinking distilled water
Drinking distilled water is quite common.

Many beverage manufacturers use distilled water to ensure a drink's purity and taste. Bottled distilled water is sold as well, and can usually be found in supermarkets. Water purification, such as distillation, is especially important in regions where water resources or tap water is not suitable for ingesting without boiling or chemical treatment.

Water filtration devices are common in many households. Most of these devices do not distill water, though there continues to be an increase in consumer-oriented water distillers and reverse osmosis machines being sold and used. Municipal water supplies often add 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 does eliminate nearly all of these impurities.

Distilled water is also used as drinking water in arid seaside areas which do not have sufficient freshwater, by distilling seawater. It is quite common on ships, especially nuclear powered ships, which require a large supply of distilled water as coolant. The drinking water is produced in desalination plants, although it is very expensive due to the large amount of fuel needed to boil water. Alternative technologies like reverse osmosis are becoming increasingly important in this regard due to their greatly reduced costs.

Pros and cons
The drinking of distilled water has been both advocated and discouraged for health reasons. 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 concluded, "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," and further encouraged individuals 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, supplemental mineral intake through diet is needed to maintain proper health.

It is often observed that consumption of "hard" water, or water that has some 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. Since distilled water is free of minerals, it will not have these potential benefits.

It has been suggested that -- because distilled water lacks fluoride ions that are added by many governments (e.g. municipalities in the United States) at water treatment plants using fluoridation for its supposed effect on the inhibition of cavity formation -- the drinking of distilled water may increase the risk of tooth decay due to a lack of this element.

The costs associated with water distillation have generally been prohibitive. However, distilling water with solar water distillers is becoming increasingly popular around the world; they can be relatively simple to design and build.

Myths
A popular myth about distilled water is that it has the dangerous property of being more easily heated above its normal boiling point without actually boiling (as seen in Mythbusters) in a process known as superheating. When superheated water is disturbed or has impurities added to it, a nucleation center for bubbles form. These bubbles are then new nucleation centers, and a sudden, explosive boiling can occur, possibly causing serious injury to those nearby. However, distilled water and tap water do not differ in their ease of or danger in being superheated. The dissolved impurities in motionless tap water do not present enough disturbance to inhibit superheating.