Purified water
Purified water is
Purified water has many uses, largely in the production of medications, in science and engineering laboratories and industries, and is produced in a range of purities. It is also used in the commercial
Parameters of water purity
Purified water is usually produced by the purification of
- inorganic ions (typically monitored as electrical conductivity or resistivity or specific tests)
- organic compounds (typically monitored as TOC or by specific tests)
- bacteria (monitored by total viable counts or epifluorescence)
- endotoxins and nucleases (monitored by LAL or specific enzyme tests)
- particulates (typically controlled by filtration)
- gases (typically managed by degassing when required)
Purification methods
Distillation
Distilled water is produced by a process of distillation.[1] Distillation involves boiling the water and then condensing the vapor into a clean container, leaving solid contaminants behind. Distillation produces very pure water.[2] A white or yellowish mineral scale is left in the distillation apparatus, which requires regular cleaning. Distilled water, like all purified water, must be stored in a sterilized container to guarantee the absence of bacteria. For many procedures, more economical alternatives are available, such as deionized water, and are used in place of distilled water.
Double distillation
Double-distilled water (abbreviated "ddH2O", "Bidest. water" or "DDW") is prepared by slow boiling the uncontaminated condensed water vapor from a prior slow boiling. Historically, it was the de facto standard for highly purified laboratory water for biochemistry and used in laboratory trace analysis until combination purification methods of water purification became widespread.[citation needed]
Deionization
Deionized water (DI water, DIW or de-ionized water), often synonymous with demineralized water / DM water,
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
Three types of deionization exist: co-current, counter-current, and mixed bed.
Co-current deionization
Co-current deionization refers to the original downflow process where both input water and regeneration chemicals enter at the top of an ion-exchange column and exit at the bottom. Co-current operating costs are comparatively higher than counter-current deionization because of the additional usage of regenerants. Because regenerant chemicals are dilute when they encounter the bottom or finishing resins in an ion-exchange column, the product quality is lower than a similarly sized counter-flow column.
The process is still used, and can be maximized with the fine-tuning of the flow of regenerants within the ion exchange column.
Counter-current deionization
Counter-current deionization comes in two forms, each requiring engineered internals:
- Upflow columns where input water enters from the bottom and regenerants enter from the top of the ion exchange column.
- Upflow regeneration where water enters from the top and regenerants enter from the bottom.
In both cases, separate distribution headers (input water, input regenerant, exit water, and exit regenerant) must be tuned to: the input water quality and flow, the time of operation between regenerations, and the desired product water analysis.
Counter-current deionization is the more attractive method of ion exchange. Chemicals (regenerants) flow in the opposite direction to the service flow. Less time for regeneration is required when compared to cocurrent columns. The quality of the finished product can be as low as .5 parts per million. The main advantage of counter-current deionization is the low operating cost, due to the low usage of regenerants during the regeneration process.
Mixed bed deionization
Mixed bed deionization is a 40/60 mixture of cation and anion resin combined in a single ion-exchange column. With proper pretreatment, product water purified from a single pass through a mixed bed ion exchange column is the purest that can be made. Most commonly, mixed bed demineralizers are used for final water polishing to clean the last few ions within water prior to use. Small mixed bed deionization units have no regeneration capability. Commercial mixed bed deionization units have elaborate internal water and regenerant distribution systems for regeneration. A control system operates pumps and valves for the regenerants of spent anions and cations resins within the ion exchange column. Each is regenerated separately, then remixed during the regeneration process. Because of the high quality of product water achieved, and because of the expense and difficulty of regeneration, mixed bed demineralizers are used only when the highest purity water is required.
Softening
Softening consists in preventing the possible precipitation of poorly soluble minerals from natural water due to changes occurring in the physico-chemical conditions (such as
Demineralization
In the strict sense, the term demineralization should imply removing all dissolved mineral species from water. Thus not only removing dissolved salt as obtained by simple deionization, but also neutral dissolved species such as dissolved
Other processes
Other processes are also used to purify water, including
Uses
Purified water is suitable for many applications, including autoclaves, hand-pieces, laboratory testing, laser cutting, and automotive use. Purification removes contaminants that may interfere with processes, or leave residues on 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. The conductivity of sea-water is typically 5 S/m,[5] 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 (0.055 μS/cm), a ratio of about 1,000,000:1,000:1.
Purified water is used in the pharmaceutical industry. Water of this grade is widely used as a raw material, ingredient, and solvent in the processing, formulation, and manufacture of pharmaceutical products, active pharmaceutical ingredients (APIs) and intermediates, compendial articles, and analytical reagents. The microbiological content of the water is of importance and the water must be regularly monitored and tested to show that it remains within microbiological control.[6]
Purified water is also used in the commercial beverage industry as the primary ingredient of any given trademarked bottling formula, in order to maintain critical consistency of taste, clarity, and color. This guarantees the consumer reliably safe and satisfying drinking. In the process prior to filling and sealing, individual bottles are always rinsed with deionised water to remove any particles that could cause a change in taste.
Deionised and distilled water are used in lead–acid batteries to prevent erosion of the cells, although deionised water is the better choice as more impurities are removed from the water in the creation process.[7]
Laboratory use
Technical standards on water quality have been established by a number of professional organizations, including the American Chemical Society (ACS), ASTM International, the U.S. National Committee for Clinical Laboratory Standards (NCCLS) which is now CLSI, and the U.S. Pharmacopeia (USP). The ASTM, NCCLS, and ISO 3696 or the International Organization for Standardization classify purified water into Grade 1–3 or Types I–IV depending on the level of purity. These organizations have similar, although not identical, parameters for highly purified water.
Note that the European Pharmacopeia uses Highly Purified Water (HPW) as a definition for water meeting the quality of Water For Injection, without however having undergone distillation. In the laboratory context, highly purified water is used to denominate various qualities of water having been "highly" purified.
Regardless of which organization's water quality norm is used, even Type I water may require further purification depending on the specific laboratory application. For example, water that is being used for molecular-biology experiments needs to be
Contaminant | Parameter | ISO 3696 (1987) | ASTM (D1193-91) | NCCLS (1988) | Pharmacopoeia | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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 | 18.2 | 1.0 | 4.0 | 0.2 | >10 | >1 | >0.1 | >0.23 | >0.77 |
Conductivity at 25 °C [μS·cm−1] | 0.1 | 1.0 | 5.0 | 0.055 | 1.0 | 0.25 | 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 Carbon/p.p.b.(μg/L) | - | - | - | 10 | 50 | 200 | - | <50 | <200 | <1000 | <500 | <500 |
Total Solids | mg/kg | - | 1 | 2 | - | - | - | - | 0.1 | 1 | 5 | - | - |
Colloids | Silica [μg/mL] | - | - | - | <2 | <3 | <500 | - | <0.05 | <0.1 | <1 | - | - |
Bacteria | CFU/mL | - | - | - | \ - | - | - | - | <10 | <1000 | - | <100 | <100 |
* Requires use of 0.2 μm membrane filter
**Prepared by distillation
***Requires the use of 0.45 μm membrane filter
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."[9]
Electrical conductivity
Completely de-gassed ultrapure water has a conductivity of 1.2 × 10−4 S/m, whereas on equilibration to the atmosphere it is 7.5 × 10−5 S/m due to dissolved CO2 in it.
Industrial uses
Some industrial processes, notably in the semiconductor and pharmaceutical industries, need large amounts of very pure water. In these situations, feedwater is first processed into purified water and then further processed to produce ultrapure water.
Another class of ultrapure water used for pharmaceutical industries is called Water-For-Inject (WFI), typically generated by multiple distillation or compressed-vaporation[check spelling] process of DI water or RO-DI water. It has a tighter bacteria requirement as 10 CFU per 100 mL, instead of the 100 CFU per mL per USP.
Other uses
Distilled or deionized water is commonly used to top up the
Distilled or deionized water is preferable to tap water for use in automotive cooling systems.
Using deionised or distilled water in appliances that evaporate water, such as
Purified water is used in freshwater and marine aquariums. Since it does not contain impurities such as copper and chlorine, it helps to keep 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) has been used to extend the performance of aircraft engines. In piston engines, it acts to delay the onset of engine knocking. 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 models.[14] 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. "Aqua" is the standard name for water in the International Nomenclature of Cosmetic Ingredients standard, which is mandatory on product labels in some countries.
Because of its high relative
Distilled water can be used in PC water-cooling systems and Laser Marking Systems. The lack of impurity in the water means that the system stays clean and prevents a buildup of bacteria and algae. Also, the low conductance reduces the risk of electrical damage in the event of a leak. However, deionized water has been known to cause cracks in brass and copper fittings.[citation needed]
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; 5,000 psi) of pressure. The extremely fine mist produced takes the heat out of 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.[15][16][17]
Distilled or purified water is used in
Window cleaners using water-fed pole systems also use purified water because it enables the windows to dry by themselves leaving no stains or smears. The use of purified water from water-fed poles also prevents the need for using ladders and therefore ensure compliance with Work at Height Legislation in the UK.
Mineral consumption
Distillation removes all minerals from water, and the
Municipal water supplies often add or have trace impurities at levels that are regulated to be safe for consumption. Much of these additional impurities, such as
are not removed through conventional filtration; however, distillation and reverse osmosis eliminate nearly all of these impurities.See also
References
- ^ "Frequently asked questions about bottled water". Health Canada. 23 November 2000. Retrieved 24 May 2009.
- ^ Buddies, Science. "Separation by Distillation". Scientific American. Retrieved 26 February 2023.
- ^ Mischissin, Stephen G. (7 February 2012). "University of Rochester - Investigation of Steam Turbine Extraction Line Failures" (PDF). Arlington, VA. pp. 25–26. Archived from the original (PDF) on 23 September 2015. Retrieved 23 February 2015.
- ^ "Deionised Water 25L". Image2output.com. 21 December 2008. Archived from the original on 2 April 2015. Retrieved 11 December 2011.
- ^ "Water conductivity". Lenntech. Retrieved 11 December 2011.
- PMID 15368993.
- ^ "What is Deionised Water? | Fortis Battery Care". Your Forklift Battery System Sorted | Fortis Battery Care. Retrieved 15 April 2016.
- ^ "The Importance of Water Quality is Critical". Archived from the original on 3 July 2016. Retrieved 25 September 2011.
- ^ "A Critique of ASTM Standard D1193".
{{cite journal}}
: Cite journal requires|journal=
(help) - PMID 16851085. See in particular page 1235. Note that values in this paper are given in S/cm, not S/m, which differs by a factor of 100.
- ^ Conductivity
- ^ "How to Buy a Steam Iron". Consumersearch.com. Retrieved 11 December 2011.
- ^ "Steam Iron Buying Guide". Homeinstitute.com. Retrieved 11 December 2011.
- ^ SP-4221 The Space Shuttle Decision Retrieved 25 April 2008
- ^ [1] Archived March 6, 2009, at the Wayback Machine
- ^ [2] Archived October 19, 2008, at the Wayback Machine
- ^ "Archived copy" (PDF). Archived from the original (PDF) on 8 February 2018. Retrieved 22 March 2009.
{{cite web}}
: CS1 maint: archived copy as title (link) - ISBN 92-4-159398-9.
- ^ "Walton International - Home". Watersystems.walton.com. 5 November 2010. Archived from the original on 4 September 2014. Retrieved 11 December 2011.
- ^ "Our Technology - Purification Technology". Drinkmorewater.com. Archived from the original on 6 January 2012. Retrieved 11 December 2011.
- ^ Technical Information - HEC-3000 10-Step Water Purification System