Portable water purification
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2008-07-07T22:17:08Z
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/* Drinking water hazards */
{{Unreferenced|date=January 2008}}
'''Portable water purification''' devices — also known as '''point-of-use''' (POU) '''water treatment systems''' and '''field water disinfection''' techniques — are self-contained units that can be used by recreational enthusiasts, military personnel, and others who must obtain drinking water from untreated sources (e.g., rivers, lakes, etc). The objective of these personal devices is to render [[Chlorination|unchlorinated]] water potable (i.e., safe and palatable for drinking purposes).
Many commercial portable drinking water systems or chemical additives are available for hiking, camping, and travel in remote areas. These devices are not only used for remote or rural areas. They can also be used to treat safe municipal water for aesthetic purposes by removing chlorine, bad taste, heavy metals like lead and mercury, and odors.
==Drinking water hazards==
Large rivers may be polluted with [[Sewage treatment|sewage effluent]], surface runoff or industrial [[pollutant]]s from sources far upstream. However even small streams, springs and wells may be contaminated by animal waste and pathogens. The presence of dead animals upstream is not uncommon.
In most parts of the world, water may contain [[bacterium|bacterial]] or [[Protozoa]] contamination originating from human and animal waste or pathogens which use other organisms as an intermediate host.
''[[Giardia lamblia]]'' and ''[[Cryptosporidium]] spp.'', both of which cause [[diarrhea]] (see [[giardiasis]] and [[cryptosporidiosis]]) are common pathogens, although in backcountry areas of the United States and Canada, they are not present in sufficient quantity to justify water treatment for backpackers [http://www.ncbi.nlm.nih.gov/pubmed/10737847?dopt=Citation] [http://lomaprieta.sierraclub.org/pcs/articles/giardia.asp].
Less commonly in developed countries are organisms such as ''[[Vibrio cholerae]]'' which causes [[cholera]] and various strains of ''[[Salmonella]]'' which cause [[typhoid]] and para-typhoid diseases. Pathogenic [[virus]]es may also be found in water. The larvae of [[Fasciola hepatica|flukes]] are particularly dangerous in area frequented by [[sheep]], [[deer]] or [[cattle]]. If such [[Microscope|microscopic]] larvae are ingested, they can form potentially life threatening [[cyst]]s in the [[brain]] or [[liver]]. This risk extends to plants grown in or near water including the commonly eaten [[watercress]].
==Techniques==
===Boiling===
[[Boiling]] is the best method to make water safe to drink. Boiling water kills bacteria. Boiling water will kill disease causing microorganisms like [[Giardia lamblia]] and [[Cryptosporidium]] which are commonly found in rivers and lakes. At high elevations, though, the [[boiling point]] of water drops, so that extra boiling time is required. Water temperatures above 70°C will kill all pathogens within 30 minutes, above 85°C within a few minutes, and at boiling point (100°C), MOST pathogens will be killed, excluding certain pathogens and their spores, which must be heated to 118 degrees celsius (eg: botulism - Clostridium botulinum). This can be achieved by using a pressure cooker, as regular boiling will not heat water past 100 degrees.
===Filtration===
Portable pump filters are commercially available with ceramic filters that filter 5000 to 50,000 litres per cartridge, removing contaminants down to the 0.2 – 0.3 [[micrometer]] range. Some also utilize activated charcoal filtering. Most filters of this kind remove bacteria and protozoa, such as ''Cryptosporidium'' and ''Giardia lamblia,'' but not viruses, so disinfection by chemicals or [[Ultraviolet|ultraviolet light]] is required after filtration. Effective chemical additives include [[chlorine]], [[chlorine dioxide]], [[iodine]], and [[sodium hypochlorite]] (bleach). There have been polymer and ceramic filters on the market that incorporated iodine post-treatment in their filter elements to kill viruses, but most have disappeared due to the unpleasant taste imparted to the water, as well as possible adverse health effects when iodine is ingested over protracted periods.
Small, hand-pumped [[reverse osmosis]] filters were originally developed for the military in the late 1980s for use as survival equipment, for example, to be included with inflatable rafts on aircraft. Civilian versions are available. Instead of using the static pressure of a water supply line to force the water through the filter, pressure is provided by a hand-operated pump, similar in function and appearance to a mechanic's [[Grease gun (tool)|grease gun]]. These devices can generate drinkable water from seawater.
While the filtration elements may do an excellent job of removing bacteria and fungi contaminants from drinking water when new, the elements themselves can become colonization sites. In recent years some filters have been enhanced by bonding [[silver]] metal nanoparticles to the ceramic element and/or to the activated charcoal to suppress growth of pathogens.
===Chemical disinfection===
[[Iodine]] is added to water as a solution, crystallized, or in tablets. The iodine kills many — but not all — of the most common pathogens present in natural fresh water sources. Carrying iodine for water purification is an imperfect but lightweight solution for those in need of field purification of drinking water. Kits are available in camping stores that include an iodine pill and a second pill (vitamin C or [[ascorbic acid]]) that will remove the iodine taste from the water after it has been disinfected. The addition of vitamin C, in the form of a pill or in flavored drink powders, precipitates much of the iodine out of solution, thus it should not be added until iodine has had sufficient time to work. This time is 30 minutes in relatively clear, warm water, but is considerably longer if the water is turbid or cold.
Chlorine-based [[bleach]] may be used for emergency disinfection. Add 2 drops of 5% bleach per litre or quart of clear water, then let stand covered for 30 to 60 minutes. After this it may be left open to reduce the chlorine smell and taste. Guidelines are available online for dangerous and effective use of bleach. {{ref|1 EPA}}, {{ref|2 BC Health}} [[USAID]] is promoting a similar product (a sodium hypochlorite solution) which is sold in developing countries specifically for the purpose of disinfecting drinking water.
Neither chlorine (e.g., bleach) nor iodine alone is considered effective against ''[[Cryptosporidium]]'', and they are partially effective against ''[[Giardia]]''. Iodine should be allowed at least 30 minutes to kill Giardia. Chlorine is slightly better than iodine against ''Giardia''.
An '''improved alternative''' to Iodine and other preparations is Silver ion/Chlorine Dioxide based tablets or droplets. Sold under names like [http://products.katadyn.com/brands-and-products/produkte/Micropur_Forte_232.html Micropur Forte], [http://www.aquamira.com/consumer/aquamira-water-treatment-2oz/ Aquamira], and [http://www.pristinewatertreatment.com/ Pristine], these solutions can disinfect water more effectively than Iodine while leaving hardly any noticeable taste in the water. The disinfecting agent will kill ''Cryptosporidum'' and ''Giardia'' if utilized correctly. The primary downside is the purification time which is generally 30 minutes to 4 hours, depending on the formulation used.
===Ultraviolet purification===
[[Ultraviolet]] (UV) light destroys [[DNA]] and thereby prevents microbes from reproducing. Without reproduction the microbes become far less dangerous. Germicidal UV light in the range of 240–290 nm acts on [[thymine]], one of the four base [[nucleotide]]s in DNA. When a germicidal UV [[photon]] is absorbed by a thymine molecule that is adjacent to another thymine within the DNA strand, a [[covalent bond]] or [[dimer]] between the molecules is created. This thymine dimer prevents [[enzyme]]s from "reading" the DNA and copying it, thus neutering the microbe. Hydro-Photon introduced the portable UV water purifer, with the brand name [http://www.betterhealthinnovations.com/Portable_Water_Purification_Steripen_UV_Ultraviolet_s/29.htm SteriPEN]. These UV water purifiers are lightweight and work very quickly.
===Solar water disinfection===
In solar water disinfection ([[SODIS]]) microbes are destroyed by temperature and [[Ultraviolet#Explanation|UVA]] radiation provided by the [[sun]]. Water is placed in a transparent plastic bottle, which is oxygenated by shaking. It is placed for six hours in full sun, which raises the temperature and gives an extended dose of solar radiation, killing some microbes that may be present. The combination of the two provides a simple method of disinfection for tropical developing countries.
===Solar distillation===
{{main|Solar still}}
Solar distillation may use a pre-manufactured and easily portable still, commonly referred to as a solar still, but it has its roots in a makeshift still that can be constructed simply from readily available components. The solar still relies on sunlight to warm and evaporate the water to be purified. The water vapour condenses, usually on a plastic sheet suspended as an inverted cone, dripping into a collection dish placed beneath its center. Note that while the solar still shares exposure to UV and infra-red radiation with SODIS, it is essentially a completely different mechanism and the two should not be confused. In an extreme survival situation the solar still can be used to prepare safe drinking water from usually unsuitable sources, such as one's own urine.
===Prevention of water contamination===
Only in very high-use wilderness areas is it recommended that '''all''' waste be packed up and carted out to a properly designated disposal point. The vast majority of the time it is perfectly safe to bury human waste, 200 feet or more from surface water.
==Controversy==
:''Main article: [[Wilderness diarrhea]]''
Although it is sometimes believed that [[water]] found in backcountry or [[wilderness]] areas is clean and [[potable]], many people believe this water is potentially unsafe to drink. Yet at least two large-scale reviews of scientific literature have failed to turn up evidence that untreated surface water in wilderness areas of the U.S. and Canada. constitutes a health hazard.
Both of these reviews conclude with similar statements suggesting that filters and chemical treatments are generally not necessary in U.S. and Canadian wilderness regions. [http://www.ncbi.nlm.nih.gov/pubmed/10737847?dopt=Citation] [http://lomaprieta.sierraclub.org/pcs/articles/giardia.asp].
The reviews suggest that backpackers are indeed prone to gastrointestinal disease through a combination of insufficient hand washing and the sharing of food. The distress is often mistakenly attributed to drinking untreated surface water.
==See also==
*[[Traveler's diarrhea]]
[[Category:Water]]