Purified water - AbsoluteAstronomy.com

Purified water is water from any source that is physically processed to remove impurities. Distilled water

Distilled water

Distilled water is water that has many of its impurities removed through distillation. Distillation involves boiling the water and then condensing the steam into a clean container.-History:...

and deionized (DI) water have been the most common forms of purified water, but water can also be purified by other processes including reverse osmosis

Reverse osmosis

Reverse osmosis is a membrane technical filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and...

, carbon filtration, microfiltration

Microfiltration

Microfiltration is a membrane technical filtration process which removes contaminants from a fluid by passage through a microporous membrane. A typical microfiltration membrane pore size range is 0.1 to 10 micrometres...

, ultrafiltration

Ultrafiltration

Ultrafiltration is a variety of membrane filtration in which hydrostatic pressure forces a liquid against a semipermeable membrane. Suspended solids and solutes of high molecular weight are retained, while water and low molecular weight solutes pass through the membrane...

, ultraviolet

Ultraviolet

Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...

oxidation, or electrodialysis

Electrodialysis

Electrodialysis is used to transport salt ions from one solution through ion-exchange membranes to another solution under the influence of an applied electric potential difference. This is done in a configuration called an electrodialysis cell...

. 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. Purified water in colloquial English can also refer to water which has been treated ("rendered potable") to neutralize, but not necessarily remove contaminants considered harmful to humans and/or animals.

Distilled water is often defined as bottled water that has been produced by a process of distillation and has an electrical conductivity

Conductivity (electrolytic)

The conductivity of an electrolyte solution is a measure of its ability to conduct electricity. The SI unit of conductivity is siemens per meter ....

of not more than 10 µS

Siemens (unit)

The siemens is the SI derived unit of electric conductance and electric admittance. Conductance and admittance are the reciprocals of resistance and impedance respectively, hence one siemens is equal to the reciprocal of one ohm, and is sometimes referred to as the mho. In English, the term...

/cm and total dissolved solids of less than 10 mg/litre. Distillation involves boiling

Boiling

Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the liquid is equal to the pressure exerted on the liquid by the surrounding environmental pressure. While below the boiling point a liquid...

the water and then condensing the vapour into a clean container, leaving solid contaminants behind. Distillation produces very pure water but also leaves behind a white or yellowish mineral scale on the distillation apparatus, which requires that the apparatus be frequently cleaned. Distillation does not guarantee the absence of bacteria in drinking water; unless the reservoir and/or bottle are sterilized before being filled, and once the bottle has been opened, there is a risk of presence of bacteria.

For many applications, cheaper alternatives such as deionized water are used in place of distilled water.

Double distillation

Double-distilled water (abbreviated "ddH₂O", "Bidest. water" or "DDW") is prepared by double distillation

Distillation

Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....

of water. Historically, it was the de facto standard for highly purified laboratory water for biochemistry

Biochemistry

Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...

and trace analysis until combination methods of purification became widespread.

Deionization

Deionized water, also known as demineralized water (DI water, DIW or de-ionized water), is water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

that has had its mineral ions removed, such as cations from sodium

Sodium

Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

, calcium

Calcium

Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

, iron

Iron

Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

, copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

and anions such as chloride

Chloride

The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...

and bromide

Bromide

A bromide is a chemical compound containing bromide ion, that is bromine atom with effective charge of −1. The class name can include ionic compounds such as caesium bromide or covalent compounds such as sulfur dibromide.-Natural occurrence:...

. 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 by incidental trapping in the resin. Specially made strong base anion resins can remove Gram-negative

Gram-negative

Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...

bacteria. Deionization can be done continuously and inexpensively using electrodeionization

Electrodeionization

Electrodeionization is usually considered a water treatment technology that utilizes an electrode to ionize water molecules and separate dissolved ions from water...

.

Deionization does not remove the hydroxide

Hydroxide

Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...

or hydronium

Hydronium

In chemistry, a hydronium ion is the cation , a type of oxonium ion produced by protonation of water. This cation is often used to represent the nature of the proton in aqueous solution, where the proton is highly solvated...

ions from water. These are the products of the self-ionization of water

Self-ionization of water

The self-ionization of water is the chemical reaction in which a proton is transferred from one water molecule to another, in pure water or an aqueous solution, to create the two ions, hydronium, H3O+ and hydroxide, OH−...

to equilibrium

Chemical equilibrium

In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. It occurs only in reversible reactions, and not in irreversible reactions. Usually, this state results when the forward reaction proceeds at the same...

and therefore are impossible to remove.

Other processes

Other processes are also used to purify water, including reverse osmosis

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. Processes rendering water potable but not necessarily closer to being pure H₂O / hydroxide

Hydroxide

+ hydronium

Hydronium

ions include use of dilute sodium hypochlorite

Bleach

Bleach refers to a number of chemicals that remove color, whiten, or disinfect, often via oxidation. Common chemical bleaches include household chlorine bleach , lye, oxygen bleach , and bleaching powder...

, mixed-oxidants (electro-catalyzed H₂O + NaCl), and iodine; See discussion regarding potable water treatments under "Health effects" below.

Uses

Purified water is suitable for many applications, including autoclaves, hand-pieces, laboratory testing, laser cutting, and automotive use. Purification removes contaminants which may interfere with processes, or leave residues upon evaporation. Although water is generally considered to be a good electrical conductor—for example domestic electrical systems are considered particularly hazardous to people if they may be in contact with wet surfaces—pure water is a poor conductor. Conductivity of sea-water is typically 5 S/m, drinking water is typically in the range of 5-50 mS/m, while highly purified water can be as low as 5.5 μS/m, a ratio

Ratio

In mathematics, a ratio is a relationship between two numbers of the same kind , usually expressed as "a to b" or a:b, sometimes expressed arithmetically as a dimensionless quotient of the two which explicitly indicates how many times the first number contains the second In mathematics, a ratio is...

of about 1,000,000:1,000:1.

Laboratory use

Technical standards on water quality have been established by a number of professional organizations, including the American Chemical Society

American Chemical Society

The American Chemical Society is a scientific society based in the United States that supports scientific inquiry in the field of chemistry. Founded in 1876 at New York University, the ACS currently has more than 161,000 members at all degree-levels and in all fields of chemistry, chemical...

(ACS), ASTM International

ASTM International

ASTM International, known until 2001 as the American Society for Testing and Materials , is an international standards organization that develops and publishes voluntary consensus technical standards for a wide range of materials, products, systems, and services...

, the U.S. National Committee for Clinical Laboratory Standards (NCCLS) which is now CLSI

Clinical and Laboratory Standards Institute

Clinical and Laboratory Standards Institute is a volunteer driven, membership supported, nonprofit, standards organization. CLSI promotes the development and use of voluntary laboratory consensus standards and guidelines within the health care community....

, and the U.S. Pharmacopeia (USP)

United States Pharmacopeia

The United States Pharmacopeia is the official pharmacopeia of the United States, published dually with the National Formulary as the USP-NF. The United States Pharmacopeial Convention is the nonprofit organization that owns the trademark and copyright to the USP-NF and publishes it every year...

. The ASTM, NCCLS, and ISO 3696 classify purified water into Grade 1–3 or Types I–IV depending upon the level of purity. These organizations have similar, although not identical, parameters for highly purified water.

Regardless of which organization's water quality norm 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 needs to be DNase or RNase-free, which requires special additional treatment or functional testing. Water for microbiology experiments needs to be completely sterile, which is usually accomplished by autoclaving. Water used to analyze trace metals may require elimination of trace metals to a standard beyond that of the Type I water norm.

Maximum Contaminant Levels in Highly Purified Water
		ISO 3696 (1987)			ASTM (D1193-91)				NCCLS (1988)			Pharmacopoeia
Contaminant	Parameter	Grade 1	Grade 2	Grade 3	Type I*	Type II**	Type III***	Type IV	Type I	Type II	Type III	EP (20°C)	USP
Ions	Resistivity at 25 °C/MΩ·cm	10	1	0.2	18	1.0	0.25	0.2	>10	>1	>0.1	>0.23	>0.77
	Conductivity at 25 °C/μS·cm⁻¹	0.1	1.0	5.0	0.056	1.0	4.0	5.0	<0.1	<1	<10	<4.3	<1.3
Acidity/Alkalinity	pH at 25 °C	-	-	5.0–7.5	-	-	-	5.0–8.0	-	-	5.0–8.0	-	-
Organics	Total Organic Content/p.p.b.(μg/l)	-	-	-	50	50	200	-	<50	<200	<1000	<500	<500
Total Solids	mg/kg	-	1	2	-	-	-	-	0.1	1	5	-	-
Colloids	Silicia/μg/mL	-	-	-	<3	<3	<500	-	<0.05	<0.1	<1	-	-
Bacteria	CFU/mL
-	-	-	-	-	-	<10	<1000	-	<100	<100

Criticism

A member of the ASTM D19 (Water) Committee, Erich L. Gibbs, criticized ASTM Standard D1193, by saying "Type I water could be almost anything – water that meets some or all of the limits, part or all
of the time, at the same or different points in the production process."

Electrical Conductivity

Electrical conductivity of ultra-pure water is 5.5 × 10⁻⁶ S·m⁻¹ (18 MΩ cm) and is due only to H⁺ and OH^- ions produced in the water dissociation equilibrium. This low conductivity is only achieved, however, in the presence of dissolved monoatomic gases. Completely de-gassed ultra-pure water has conductivity of 1.2 × 10⁻⁴ S·m⁻¹, whereas upon equilibration to the atmosphere it is 7.5 × 10⁻⁵ S·m⁻¹ due to dissolved CO₂ in it.
The highest grades of ultrapure water should not be stored in glass or plastic containers because these container materials leach (release) contaminants at very low concentrations. Storage vessels made of silica are used for less demanding applications and vessels of ultrapure tin

Tin

Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...

are used for the highest purity applications.

Examples of laboratory quality sources include Milli-Q

Milli-Q

Milli-Q is a trademark created by Millipore Corporation to describe 'ultrapure' water of "Type 1", as defined by various authories , as well as their devices for producing such water. The purification processes involve successive steps of filtration and deionisation, to achieve a purity...

, Elga Ultra, or Purite Neptune.

Non-laboratory uses

Distilled or deionized water is commonly used to top up lead-acid batteries used in cars and trucks and for other applications. The presence of foreign ions commonly found in tap water will drastically shorten the lifespan of a lead-acid battery.

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

Antifreeze

Antifreeze is a freeze preventive used in internal combustion engines and other heat transfer applications, such as HVAC chillers and solar water heaters....

formulations. Distilled or deionized water is especially important in automotive hybrid

Hybrid vehicle

A hybrid vehicle is a vehicle that uses two or more distinct power sources to move the vehicle. The term most commonly refers to hybrid electric vehicles , which combine an internal combustion engine and one or more electric motors.-Power:...

system component cooling systems, mixed with hybrid system coolant, to prevent corrosion or electrolysis of hybrid components.

Using deionised or distilled water in appliances which evaporate water, such as steam irons and humidifiers, can reduce the build-up of mineral scale

Limescale

Limescale is the hard, off-white, chalky deposit found in kettles, hot-water boilers and the inside of inadequately maintained hot-water central heating systems...

, which shortens appliance life. Some appliance manufacturers say that deionised water is no longer necessary.

Purified water is used in freshwater and marine aquarium

Aquarium

An aquarium is a vivarium consisting of at least one transparent side in which water-dwelling plants or animals are kept. Fishkeepers use aquaria to keep fish, invertebrates, amphibians, marine mammals, turtles, and aquatic plants...

s. Since it does not contain impurities such as copper and chlorine, it helps to keeps fish free from diseases, and avoids the build-up of algae on aquarium plants due to its lack of phosphate and silicate. Deionized water should be re-mineralized before use in aquaria, since it lacks many macro- and micro-nutrients needed by plants and fish.

Water (sometimes mixed with methanol

Methanol

Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...

) has been used to extend the performance of aircraft engines. In piston engines it acts to delay the onset of engine knocking

Engine knocking

Knocking in spark-ignition internal combustion engines occurs when combustion of the air/fuel mixture in the cylinder starts off correctly in response to ignition by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.The...

. In turbine engines it allows more fuel flow for a given turbine temperature limit, and increases mass flow. As an example, it was used on early Boeing 707

Boeing 707

The Boeing 707 is a four-engine narrow-body commercial passenger jet airliner developed by Boeing in the early 1950s. Its name is most commonly pronounced as "Seven Oh Seven". The first airline to operate the 707 was Pan American World Airways, inaugurating the type's first commercial flight on...

models. Advanced materials and engineering have since rendered such systems obsolete for new designs, however spray-cooling of incoming air-charge is still used to a limited extent with off-road turbo-charged engines (road-race track cars).

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; see International Nomenclature of Cosmetic Ingredients.

Because of its high relative dielectric constant

Dielectric constant

The relative permittivity of a material under given conditions reflects the extent to which it concentrates electrostatic lines of flux. In technical terms, it is the ratio of the amount of electrical energy stored in a material by an applied voltage, relative to that stored in a vacuum...

(~80), deionized water is also used (for short durations) as a high voltage dielectric in many pulsed power

Pulsed power

Pulsed power is the term used to describe the science and technology of accumulating energy over a relatively long period of time and releasing it very quickly thus increasing the instantaneous power.-Overview:...

applications, such as the Sandia National Laboratories

Sandia National Laboratories

The Sandia National Laboratories, managed and operated by the Sandia Corporation , are two major United States Department of Energy research and development national laboratories....

Z Machine

Z machine

The Z machine is the largest X-ray generator in the world and is designed to test materials in conditions of extreme temperature and pressure. Operated by Sandia National Laboratories, it gathers data to aid in computer modeling of nuclear weapons...

.

Distilled water can be used in PC watercooling systems and Laser Marking Systems. The lack of impurity in the water means that the system stays clean and prevents a build up of bacteria and algae. Also, the low conductance reduces risk of electrical damage in the event of a leak.

When used as a rinse after washing cars, windows, and similar applications, purified water dries without leaving spots caused by dissolved solutes.

Deionized water is used in water-fog fire-extinguishing systems used in sensitive environments, such as where high-voltage electrical and sensitive electronic equipment is used. The 'sprinkler' nozzles use much finer spray jets than other systems, and operate at up 35 MPa (350 bar; 5000 psi) of pressure. The extremely fine mist produced takes the heat out of a fire rapidly, and the fine droplets of water are nonconducting (when deionized) and are less likely to damage sensitive equipment. Deionized water, however, is inherently acidic and contaminants (such as copper, dust, stainless and carbon steel, and many other common materials) rapidly supply ions, thus re-ionizing the water. It is not generally considered acceptable to spray water on electrical circuits that are powered, and it is generally considered undesirable to use water in electrical contexts.

Health effects of drinking purified water

Distillation removes all minerals from water, and the membrane methods

Membrane technology

The membrane technology covers all process engineering measures for the transport of substances between two fractions with the help of permeable membranes...

of reverse osmosis and nanofiltration remove most, or virtually all, minerals. This results in demineralized water which is not an ideal replacement for drinking water

Drinking water

Drinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...

. The World Health Organization investigated the health effects of demineralized water in 1980, and its experiments in humans found that demineralized water increased diuresis

Diuresis

Diuresis may refer to:* Urine production, as an aspect of fluid balance* Excessive urine production - see polyuria* Immersion diuresis...

and the elimination of electrolyte

Electrolyte

In chemistry, an electrolyte is any substance containing free ions that make the substance electrically conductive. The most typical electrolyte is an ionic solution, but molten electrolytes and solid electrolytes are also possible....

s, with decreased serum potassium concentration. Magnesium, calcium and other nutrients in water can help to protect against nutritional deficiency. Demineralized water may also increase the risk from toxic metals because it more readily absorbs them, and because the presence of calcium and magnesium in water can prevent absorption of lead and cadmium. 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. 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

Dental fluorosis

Dental fluorosis is a developmental disturbance of dental enamel caused by excessive exposure to high concentrations of fluoride during tooth development. The risk of fluoride overexposure occurs between the ages of 3 months and 8 years. In its mild forms , fluorosis often appears as unnoticeable,...

.

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 distillers and reverse osmosis

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

Fluoride

Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides. Fluoride, like other halides, is a monovalent ion . Its compounds often have properties that are...

, 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 purified water as a replacement of drinking water has been both advocated and discouraged for health reasons. Purified water lacks minerals and ions such as calcium that play key roles in biological functions such as in nervous system homeostasis

Homeostasis

Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...

, 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

Calcium

, magnesium

Magnesium

Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

, and sodium

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, supplemental mineral intake through diet is needed to maintain proper health.

The consumption of "hard" water

Hard water

Hard water is water that has high mineral content . Hard water has high concentrations of Ca2+ and Mg2+ ions. Hard water is generally not harmful to one's health but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling...

(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

Heart disease

Heart disease, cardiac disease or cardiopathy is an umbrella term for a variety of diseases affecting the heart. , it is the leading cause of death in the United States, England, Canada and Wales, accounting for 25.4% of the total deaths in the United States.-Types:-Coronary heart disease:Coronary...

. Since distilled water is free of minerals, it will not have these potential benefits.

Where a public water supply contains significant fluoride, naturally or added by fluoridation, people who prefer to limit fluoride intake can install filters appropriate to reduce fluoride content, although this may harm dental health.

Double distillation

Deionization

Other processes

Uses

Laboratory use

Criticism

Electrical Conductivity

Non-laboratory uses

Health effects of drinking purified water

See also