Portable water purification
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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 who must obtain drinking water from untreated sources (e.g., rivers, lakes, etc). The objective of these personal devices is to render 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.
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[edit] Drinking water hazards
Large rivers may be polluted with sewage effluent, surface runoff or industrial pollutants 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 bacterial or protoist 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 [1] [2].
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 viruses may also be found in water. The larvae of flukes are particularly dangerous in area frequented by sheep, deer or cattle. If such microscopic larvae are ingested, they can form potentially life threatening cysts in the brain or liver. This risk extends to plants grown in or near water including the commonly eaten watercress.
[edit] Techniques
[edit] 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.
[edit] 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 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. 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.
[edit] 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. , 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 Micropur Forte, Aquamira, and 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.
[edit] 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 nucleotides 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 enzymes from "reading" the DNA and copying it, thus neutering the microbe. Hydro-Photon introduced the portable UV water purifer, with the brand name SteriPEN. These UV water purifiers are lightweight and work very quickly.
[edit] Solar water disinfection
In solar water disinfection (SODIS) microbes are destroyed by temperature and 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.
[edit] Solar distillation
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.
[edit] 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.
[edit] Controversy
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. [3] [4].
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.
