Natural water usually contains a number of microscopic contaminants, along with dissolved minerals such as calcium and iron. One way to remove these elements from water is to boil it until it changes to steam, a process known as distillation. When this steam is allowed to cool down and condense into liquid form again, the result is a purified form called distilled water. Distilled water should ideally be nothing but hydrogen and oxygen molecules, with a PH level of 7 and no additional gases, minerals or contaminants.

The distilling process relies on the principle that most solid materials found in water are heavier than the water molecules themselves. When water is heated in a distiller, any dissolved solids such as salt, bacteria, calcium or iron remain solid while the pure water converts to a much lighter steam and is drawn out for condensation. Distilled water has a noticeably bland taste because all of the minerals which give water its flavor have been removed.

Distilled water is safe to drink, but it is used more often for research purposes where water purity is essential or industrial uses where mineral deposits can cause damage over time. Distilled water may also be used in steam irons to prevent calcium build-up, but this requirement has generally been relaxed in recent years. Certain baby formulas may use distilled water as a mixing liquid as well. Pediatric bottled water formulated with additional electrolytes may use a distilled water base as well.

There is some controversy over the use of distilled water as a healthier alternative to tap, spring or purified water. One camp suggests that distilled water is beneficial since it contains no impurities or minerals and helps flush away excess minerals and toxins from the body. Another camp believes that distilled water leaches essential minerals from the body and could leave teeth vulnerable to damage. Distilled water does not contain sodium fluoride, unlike many municipal water systems.

There is some evidence that distilled water does absorb carbon dioxide when exposed to air, and this could conceivably raise the pH to a more acidic level. This increased acidity can in turn create more health problems. Proponents of distilled water suggest that humans receive far more minerals and nutrients from food than water, so the effects of distilled water on the body should be minimal at best. The flavor of distilled water can be improved with natural fruit juices or essences, if necessary.

Distilled water can be purchased in a number of grocery and retail stores, usually in one gallon containers. It is important to check the label when shopping for bottled water of any kind, since distilled water has a distinctive taste compared to spring or purified water. Some bottled waters use distilled water or deionized water as a base, with different minerals added for taste.