Distilled water is water that has been boiled into vapor and condensed 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. Thus, distilled water is a type of purified water.
Drinking water has been distilled from seawater since at least about AD 200, when the process was clearly described by Alexander of Aphrodisias. [1] Its history predates this, as a passage in Aristotle's Meteorologica refers to the distillation of water. [2] Captain Israel Williams of the Friendship (1797) improvised a way to distill water, which he described in his journal. [3]
In chemical and biological laboratories, as well as in industry, in some appliances, deionized water or reverse osmosis water can be used instead of distilled water as a cheaper alternative. If exceptionally high-purity water is required, double distilled water is used.
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. [4]
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 humidors can use distilled water to avoid mineral deposits. [5]
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. [6]
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. [7] [8]
It is also possible for brewers to blend distilled water with hard water to mimic the soft waters of Pilsen. [9]
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. [10]
Distilled water can be used in steam irons for pressing clothes to minimize the build-up of limescale in hard water areas shortening the lifespan of steam irons. Some steam irons have built in filters to remove minerals from the water meaning standard tap water can be used.
Until World War II, distilling seawater to produce fresh water was time-consuming and expensive in fuel. The saying was: "It takes one gallon of fuel to make one gallon of fresh water."[ citation needed ] Shortly before the war, Dr. R. V. Kleinschmidt developed a compression still, which became known as the Kleinschmidt still, for extracting fresh water from seawater or contaminated water. By compressing the steam produced by boiling water, 175 US gal (660 L; 146 imp gal) of fresh water could be extracted from seawater for every gallon (3.8 L; 0.83 imp gal) of fuel used. During World War II this equipment became standard on Allied ships and on trailer mounts for armies. This method was in widespread use in ships and portable water distilling units [11] during the latter half of the century. Modern vessels now use flash-type evaporators to boil seawater, heating the water to between 70 and 80 °C (158 and 176 °F) and evaporating the water in a vacuum; this is then collected as condensation before being stored.
Solar stills can be relatively simple to design and build, with very cheap materials. [12]
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) due to the fact that 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). [13]
Bottled distilled water can usually be found in supermarkets or pharmacies, and home water distillers are available as well. 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.
Municipal water supplies almost always contain trace components at levels which are regulated to be safe for consumption. [14] 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. [15]
Distilled water is also used for drinking water in arid seaside areas lacking sufficient freshwater, via desalination of seawater. [16]
Distillation removes all minerals from water. This results in demineralised water, which has not been proven to be healthier than drinking water. The World Health Organization investigated the health effects of demineralised water in 1982, and its experiments in humans found that demineralised water increased diuresis and the elimination of electrolytes, with decreased serum potassium concentration.[ citation needed ] Magnesium, calcium, and other nutrients in water can help to protect against nutritional deficiency. Recommendations for magnesium have been put at a minimum of 10 mg/L with 20–30 mg/L optimum; for calcium a 20 mg/L minimum and a 40–80 mg/L optimum, and a total water hardness (adding magnesium and calcium) of 2–4 mmol/L. At water hardness above 5 mmol/L, higher incidence of gallstones, kidney stones, urinary stones, arthrosis, and arthropathies have been observed.[ citation needed ] For fluoride the concentration recommended for dental health is 0.5–1.0 mg/L, with a maximum guideline value of 1.5 mg/L to avoid dental fluorosis. [17]
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 [18] 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 potable 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. [19]
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. [20]
Distillation, also classical distillation, is the process of separating the component substances of a liquid mixture of two or more chemically discrete substances; the separation process is realized by way of the selective boiling of the mixture and the condensation of the vapors in a still.
Fluoride is an inorganic, monatomic anion of fluorine, with the chemical formula F−
, whose salts are typically white or colorless. Fluoride salts typically have distinctive bitter tastes, and are odorless. Its salts and minerals are important chemical reagents and industrial chemicals, mainly used in the production of hydrogen fluoride for fluorocarbons. Fluoride is classified as a weak base since it only partially associates in solution, but concentrated fluoride is corrosive and can attack the skin.
Desalination is a process that removes mineral components from saline water. More generally, desalination is the removal of salts and minerals from a substance. One example is soil desalination. This is important for agriculture. It is possible to desalinate saltwater, especially sea water, to produce water for human consumption or irrigation. The by-product of the desalination process is brine. Many seagoing ships and submarines use desalination. Modern interest in desalination mostly focuses on cost-effective provision of fresh water for human use. Along with recycled wastewater, it is one of the few water resources independent of rainfall.
Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for human consumption, but water purification may also be carried out for a variety of other purposes, including medical, pharmacological, chemical, and industrial applications. The history of water purification includes a wide variety of methods. The methods used include physical processes such as filtration, sedimentation, and distillation; biological processes such as slow sand filters or biologically active carbon; chemical processes such as flocculation and chlorination; and the use of electromagnetic radiation such as ultraviolet light.
Magnesium sulfate or magnesium sulphate is a chemical compound, a salt with the formula MgSO4, consisting of magnesium cations Mg2+ (20.19% by mass) and sulfate anions SO2−4. It is a white crystalline solid, soluble in water but not in ethanol.
Hard water is water that has a high mineral content. Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bicarbonates and sulfates.
Magnesium chloride is an inorganic compound with the formula MgCl2. It forms hydrates MgCl2·nH2O, where n can range from 1 to 12. These salts are colorless or white solids that are highly soluble in water. These compounds and their solutions, both of which occur in nature, have a variety of practical uses. Anhydrous magnesium chloride is the principal precursor to magnesium metal, which is produced on a large scale. Hydrated magnesium chloride is the form most readily available.
A humidifier is a household appliance or device designed to increase the moisture level in the air within a room or an enclosed space. It achieves this by emitting water droplets or steam into the surrounding air, thereby raising the humidity.
Purified water is water that has been mechanically filtered or processed to remove impurities and make it suitable for use. Distilled water was, formerly, the most common form of purified water, but, in recent years, water is more frequently purified by other processes including capacitive deionization, reverse osmosis, carbon filtering, microfiltration, ultrafiltration, ultraviolet oxidation, or electrodeionization. Combinations of a number of these processes have come into use to produce ultrapure water of such high purity that its trace contaminants are measured in parts per billion (ppb) or parts per trillion (ppt).
Water softening is the removal of calcium, magnesium, and certain other metal cations in hard water. The resulting soft water requires less soap for the same cleaning effort, as soap is not wasted bonding with calcium ions. Soft water also extends the lifetime of plumbing by reducing or eliminating scale build-up in pipes and fittings. Water softening is usually achieved using lime softening or ion-exchange resins, but is increasingly being accomplished using nanofiltration or reverse osmosis membranes.
Multi-stage flash distillation (MSF) is a water desalination process that distills sea water by flashing a portion of the water into steam in multiple stages of what are essentially countercurrent heat exchangers. Current MSF facilities may have as many as 30 stages.
Solar desalination is a desalination technique powered by solar energy. The two common methods are direct (thermal) and indirect (photovoltaic).
Boiler water is liquid water within a boiler, or in associated piping, pumps and other equipment, that is intended for evaporation into steam. The term may also be applied to raw water intended for use in boilers, treated boiler feedwater, steam condensate being returned to a boiler, or boiler blowdown being removed from a boiler.
An evaporator is a type of heat exchanger device that facilitates evaporation by utilizing conductive and convective heat transfer, which provides the necessary thermal energy for phase transition from liquid to vapour. Within evaporators, a circulating liquid is exposed to an atmospheric or reduced pressure environment causing it to boil at a lower temperature compared to normal atmospheric boiling.
A solar-powered desalination unit produces potable water from saline water through direct or indirect methods of desalination powered by sunlight. Solar energy is the most promising renewable energy source due to its ability to drive the more popular thermal desalination systems directly through solar collectors and to drive physical and chemical desalination systems indirectly through photovoltaic cells.
Bittern, or nigari, is the salt solution formed when halite precipitates from seawater or brines. Bitterns contain magnesium, calcium, and potassium ions as well as chloride, sulfate, iodide, and other ions.
Reverse osmosis (RO) is a water purification process that uses a semi-permeable membrane to separate water molecules from other substances. RO applies pressure to overcome osmotic pressure that favors even distributions. RO can remove dissolved or suspended chemical species as well as biological substances, and is used in industrial processes and the production of potable water. RO retains the solute on the pressurized side of the membrane and the purified solvent passes to the other side. The relative sizes of the various molecules determines what passes through. "Selective" membranes reject large molecules, while accepting smaller molecules.
The following outline is provided as an overview of and topical guide to water:
An evaporator, distiller or distilling apparatus is a piece of ship's equipment used to produce fresh drinking water from sea water by distillation. As fresh water is bulky, may spoil in storage, and is an essential supply for any long voyage, the ability to produce more fresh water in mid-ocean is important for any ship.
A distilling ship is a class of military ships, generally converted tankers, with the capability to convert salt water into fresh water. They were typically stationed at forward bases during conflict where they supported on-the-ground troops and front line naval units.
Short of Fresh Water Causes Alarm — Captain Williams's Invention to Make Salt Water Fresh — His 'Still' Described by him
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