Purified water
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Cleanup/[[WP:AWB/T|typo fixing]], typos fixed: flouride → fluoride using [[Project:AutoWikiBrowser|AWB]]
[[Image:Aqua-distillata.jpg|thumb|200px|[[Bottle]] for Distilled water in the [[Real Farmacia]] in [[Madrid]]]]
'''[[Purified water]]''' is water from any source that is physically processed to remove impurities. '''Distilled water''' and '''deionized water''' have been the most common forms of purified water, but water can also be purified by other processes including [[reverse osmosis]], carbon filtration, [[microporous filtration]], [[ultrafiltration]], [[ultraviolet oxidation]], or [[electrodialysis]]. In recent decades, a combination of the above processes have come into use to produce water of such high purity that its trace contaminants are measured in parts per billion (ppb) or parts per trillion (ppt). Purified water has many uses, largely in science and engineering laboratories and industries, and is produced in a range of purities.
== Methods of water purification ==
=== Distillation ===
[[Image:Condensationbag.jpg|thumb|right|150px|Gathering water through the use of a bag is a much employed [[survivalism|survival technique]] ]]
[[Image:Condensationpit.jpg|thumb|right|150px|Gathering water through the use of a pit is another much employed [[survivalism|survival technique]] ]]
'''Distilled water''' has virtually all of its [[Impurity|impurities]] removed through [[distillation]]. Distillation involves [[boiling]] the water and then condensing the [[steam]] into a clean cup, leaving nearly all of the solid contaminants behind. Distillation produces very pure water but also leaves behind a leftover white or yellowish mineral scale, which requires that the distillation apparatus be frequently cleaned.
For many applications, cheaper alternatives such as deionized water are preferred over distilled water.
=== Double-distillation ===
'''Double distilled water''' (abbreviated "ddH<sub>2</sub>O" or "Bidest. water") is prepared by double [[distillation]] of water. Historically, it was the de facto standard for highly purified laboratory water for [[biochemistry]] and [[trace analysis]] until combination methods of purification became widespread.
=== Deionization ===
'''Deionized water''' which is also known as '''demineralized water''' ('''DI water''' or '''de-ionized water'''; also spelled '''deionised water''', see [[spelling differences]]) is [[water]] that has had its minerals removed, such as [[cation]]s from [[sodium]], [[calcium]], [[iron]], [[copper]] and [[anion]]s such as [[chloride]] and [[bromide]]. Deionization is a physical process which uses specially-manufactured ion exchange resins which bind to and filter out the mineral salts from water. Because the majority of water impurities are dissolved salts, deionization produces a high purity water that is generally similar to distilled water, and this process is quick and without scale buildup. However, deionization does not significantly remove uncharged organic molecules, viruses or bacteria, except through "accidental" trapping by the resin. Specially made strong base anion resins can remove [[Gram-negative]] bacteria. Deionization can be done continuously using [[electrodeionization]].
It should be noted that removal of all ions from water is next to impossible, since water [[Self-ionization of water|self-ionizes]] quickly to reach equilibrium.
=== Other processes ===
[[Image:Homemade waterfilter.jpg|thumb|right|150px|A homemade waterfilter using charcoal (carbon), together with sand and grass is often employed for making safe drinking water]]
Other processes are also used to purify water, including reverse osmosis, carbon filtration, microporous filtration, ultrafiltration, ultraviolet oxidation, or electrodialysis. These are used in place of, or in addition to the processes listed above. Generally, each process is well suited to removing a particular set of impurities while not being as good at removing other impurities.
== Parameters of purified water ==
=== Resistivity and conductivity ===
Removal of ions causes water's [[resistivity]] to increase, providing a convenient measurement for the exact extent of deionization. Ultrapure deionized water has a theoretical maximum resistivity of 18.31 MΩ·cm and a theoretical minimum conductivity of .0545 [[Siemens (unit)|microsiemens]]/cm, compared to around 15 kΩ·cm and 70 microsiemens/cm for tap water. Deionized water's high resistivity allows it, in some very highly specialized instances, to be used as a coolant in direct contact with high-voltage electrical equipment. Because of its high relative [[dielectric constant]] (~80), it is also used (for short durations) as a high voltage dielectric in many [[pulsed power]] applications, such as Sandia's [[Z Machine]].
=== pH values ===
The theoretical [[pH]] of highly purifed water is 7.0. In practice, however, most purified water will have a pH that is slightly acidic (less than 7.0) due to the presence of dissolved [[carbon dioxide]] (CO<sub>2</sub>) from the atmosphere. Dissolved carbon dioxide reacts slowly with water to give the [[bicarbonate]] and [[hydronium]] ions.
:CO<sub>2 ''(g)''</sub> + 2H<sub>2</sub>O<sub>''(l)''</sub> ⇋ HCO<sub>3</sub><sup>-</sup> + H<sub>3</sub>O<sup>+</sup>
Note that [[carbonic acid]], H<sub>2</sub>CO<sub>3</sub>, is only formed in strongly acid solutions. Distillation temporarily removes dissolved CO<sub>2</sub> from the water. However, during condensation, water that is exposed to air will reabsorb CO<sub>2</sub> again resulting in a pH that is slightly less than 7.0.
== Uses ==
=== Laboratory use ===
Water quality standards for purified water have been established by a number of professional organizations, including the American Chemical Society (ACS), the American Society for Testing and Materials (ASTM), the National Committee for Clinical Laboratory Standards (NCCLS) which is now CLSI, and the U.S. Pharmacopeia (USP). The ASTM, NCCLS, and ISO 3696 classify purified water into Types I-III depending upon the level of purity. While there is some general consensus across these organizations on what constitutes each type of water, there are still some differences.
Most ultrapure laboratory water is currently produced by a combination of the physical purification processes described above.
Regardless of which water quality standard is used, even Type I water may require further purification depending upon the specific laboratory application. For example, water that is being used for molecular biology experiments may need to be DNase or RNase-free, whereas water for microbiology experiments needs to be completely sterile. Water used to analyze trace metals needs an even higher level of impurity removal.
{| class="wikitable"
|+ Maximum Contaminant Levels in Type I-III Purified Water <ref name="Millipore Specifications">{{cite web |url=http://www.millipore.com/labwater/lw3/watertypes |title=Laboratory Water Types}}</ref>
! Contaminant !! Parameter !! Type I !! Type II !! Type III
|-
| Ions || Resistivity at 25°C (megohms-cm) || >18.0 || >1.0 || >0.05
|-
| || Conductivity at 25°C (microsiemens/cm) || <0.056 || <1.0 || <20
|-
| Organics || TOC (ppb) || <10 || <50|| <200
|-
| Pyrogens || Eu/mL || <0.03 || NA || NA
|-
| Particulates || size || <0.2 µm|| NA || NA
|-
| Colloids || Silicia (ppb) || <10 || <100 || <1000
|-
| Bacteria || CFU/mL ||<1 || <100 || <1000
|}
The highest grades of ultrapure water should not be stored in glass or plastic containers because such materials leach contaminants at very low concentrations. Storage vessels made of [[silica]] are used for less demanding applications and of ultrapure [[tin]] for the highest purity use.
=== Other uses ===
Distilled or deionized water are commonly used to top up [[lead acid batteries]] used in cars and trucks. The presence of foreign ions commonly found in tap water will cause a drastic reduction in an automobile's battery lifespan.
Distilled or deionized 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.{{Fact|date=May 2007}} Distilled or deionized water is especially important in automotive [[hybrid]] system component cooling systems, mixed with hybrid system coolant, to prevent corrosion and/or electrolisys of hybrid components.{{fact|date=June 2007}}
Using distilled water in [[steam iron]]s for pressing clothes, as well as other appliances such as humidifiers and cigar [[humidors]] which boil water, can reduce mineral scale build-up and help the appliance last longer. However, many iron manufacturers say that distilled water is no longer necessary in their irons.{{Fact|date=February 2007}}
For treatment of [[sleep apnea]], patients using [[CPAP]] machines that have a humidifier are instructed to use distilled water so he or she does not inhale any impurities from non-purified water.
Purified water is used in freshwater and marine [[aquarium]]s. Since it does not contain impurities such as copper and chlorine, it keeps fish free from diseases, as well as avoiding the build-up of algae on aquarium plants, due to its lack of phosphate and silicate. Deionized water should be re-mineralized before used in aquaria, since it also lacks many macro and micro-nutrients needed by both plants and fish.
Another application is to cool off airplane engines before takeoff, was used on the early [[Boeing 707]]. This is not as common today due to cost.<ref>
[http://history.nasa.gov/SP-4221/ch7.htm SP-4221 The Space Shuttle Decision] Retrieved 25 Apr 2008</ref>
Deionized water is very often used as an "ingredient" in many cosmetics and pharmaceuticals where it is sometimes referred to as "aqua" on product ingredient labels. This use again owes to its lack of potential for causing undesired chemical reactions due to impurities.
Purified water can also be used in PC watercooling systems. The lack of impurity in the water means that the system stays clean and prevents a build up of bacteria and algae. This enables the machine to work at optimal efficiency even after extensive periods of time without water exchange.
A recent use of purified water is that of a final rinse in some [[car wash]]es where, because it contains no dissolved solutes, the car dries without leaving any spots. Another use of deionized water is in window cleaning, where window cleaners use pumped systems to brush and rinse windows with deionized water again without leaving any spots.
Deionized water has also recently found a use in an up to date version of water fog fire extinguishing systems. Such systems can be used in sensitive environments such as where high voltage electrical and sensitive electronic equipment is used. The 'sprinkler' nozzles use much finer spray jets and operate at up 350 bar (35 MPa, 5000 psi) of pressure. The extremely fine mist produced takes the heat out of a fire rapidly and the deionized water coupled with the fine droplets is non conducting and does not damage sensitive equipment, not already damaged by fire <http://www.hi-fog.com/en/land-applications/index_land-applications_EN.shtml>. The system is perfectly safe to discharge when personnel are present. Apart from getting a little damp, there are no other hazards associated with the system.
=== Drinking purified water ===
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 becoming increasingly common in households. Most of these devices do not distill water, though there continues to be an increase in consumer-oriented [[water distiller]]s 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{{Fact|date=February 2007}} are not removed through conventional filtration; however, distillation and reverse osmosis eliminate nearly all of these impurities.
The drinking of purified water has been both advocated and discouraged for health reasons. Purified water lacks minerals and ions, such as calcium, which are normally found in potable (drinking) water, and which have important biological functions such as in nervous system [[homeostasis]]. Some percentage of our daily consumption of these minerals and ions come from our drinking water, but most of them come from the food we eat, making DI water perfectly fine to drink if one has food in his or her system. The lack of naturally-occurring minerals in distilled water has raised some concerns. The Journal of General Internal Medicine<ref>{{Citation
| last1=Azoulay | first1=Arik
| last2=Garzon | first2=Philippe
| last3=Eisenberg | first3=Mark
| year=2001
| title=Comparison of the Mineral Content of Tap Water and Bottled Waters
| periodical=Journal of General Internal Medicine
| volume=16
| issue=3
| pages=168-175
| url=http://www.blackwell-synergy.com/links/doi/10.1111/j.1525-1497.2001.04189.x/enhancedabs/
}}</ref> 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| "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]].<ref>{{Citation
| last=Voors
| first=A. W.
| year=1971
| title=Mineral in the municipal water and atherosclerotic heart death
| periodical=American Journal of Epidemiology
| volume=93
| issue=4
| pages=259-266
| url=http://aje.oxfordjournals.org/cgi/content/abstract/93/4/259
}}</ref> 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 a minority of governments (e.g. municipalities in the United States) at water treatment plants using [[sodium hexafluorosilicate]] or [[hexafluorosilicic acid]] for their effect on the inhibition of [[caries|cavity]] formation: the drinking of distilled water may increase the risk of tooth decay due without this element. However, the benefit of fluoride supplementation for any purpose should be cautioned due to potential negative effects to IQ and motor functions<ref>[http://www.fluoridealert.org/pmullenix.htm ''Statement from Dr. Phyllis Mullenix on the Neurotoxicity of Fluoride'' at Fluoride Action Network]</ref> and a lack of strong evidence that fluoridation of drinking water is effective at cavity prevention, and fluoride is the core ingredient of toothpaste and mouthwash <ref> York Review, Executive Summary http://www.york.ac.uk/inst/crd/pdf/summary.pdf</ref> especially when compared to other ways of using fluorides.
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.{{Fact|date=August 2007}}
== See also ==
* [[Hydrogen production]]
* [[Ionized water]]
* [[Water ionizer]]
* [[Electrodeionization]]
* [[Atmospheric water generator]] ''(Make distilled water from air)''
* [[Heavy water]]
* [[Water softening]]
== References ==
<references/>
== External links ==
* [http://van.physics.uiuc.edu/qa/listing.php?id=1743 Deionized Water] (Physics Van QA Forum)
* [http://www.reskem.com/pdf/con_res_conversion.pdf] (Res-Kem Corp. Conductivity/Resistivity Conversion Chart)
[[Category:Liquid water]]
[[Category:Distillation]]
[[Category:Drinking water]]
[[Category:Coolants]]
[[Category:Dielectrics]]
[[Category:Water supply]]
[[ar:الماء المقطر]]
[[de:Demineralisiertes Wasser]]
[[de:Destilliertes Wasser]]
[[es:Agua desionizada]]
[[es:Agua destilada]]
[[fr:Eau distillée]]
[[gl:Auga destilada]]
[[ko:증류수]]
[[it:Acqua demineralizzata]]
[[it:Acqua distillata]]
[[he:מים מזוקקים]]
[[nl:Gedestilleerd water]]
[[ja:純水]]
[[ja:精製水]]
[[pl:Woda demineralizowana]]
[[pl:Woda destylowana]]
[[pt:Água destilada]]
[[ru:Дистиллированная вода]]
[[sl:Destilirana voda]]
[[fi:Tislattu vesi]]
[[sv:Destillerat vatten]]
[[zh:蒸馏水]]
[[zh:去离子水]]
[[zh:纯净水]]