Portable water purification
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There is often a need to be able to treat water in remote or rural locations, or in emergency settings, to make it safe for drinking purposes. Although it is sometimes believed that water found in backcountry or wilderness areas is clean and potable, such water is often unsafe to drink.
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 protist 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. 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 particulalrly 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.
Portable drinking water systems or chemical additives are available for hiking, camping, and travel in remote areas.
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[edit] Ultraviolet Purification
UV light destroys DNA and thereby prevents microbes from reproducing. Germicidal UV light – between about 240nm and 290nm – 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 dymer, between the molecules is created. This thymine dymer prevents enzymes from “reading” the DNA and copying it. Without the ability to replicate DNA, the microbe cannot reproduce and is rendered harmless. www.steripen.com
The referenced company's microbiological effectiveness has been tested at 3 universities (U. Maine, U. Arizona, Oregon Health Sciences U.). When used as directed, the product ( SteriPEN ) has been shown to destroy over: 99.9999% of bacteria, 99.99% of viruses and 99.9% of protozoa (i.e. Giardia and Cryptosporidium). These levels of destruction meet or exceed the requirements of the US EPA’s Guide Standard and Protocol for Testing Microbiological Water Purifiers.
[edit] Boiling
Boiling water on a portable stove kills bacteria and viruses. At high elevations, though, the boiling point of water drops, so that several minutes of continuous boiling are required. At extremely high elevations, boiling ceases to be effective.
[edit] Filters
Portable pump filters are commercially available with ceramic filters that filter 5000 to 50,000 litres per cartridge. Some also utilise activated charcoal filtering. Most filters of this kind do not remove viruses, so disinfection by chemicals or ultraviolet light is required after filtration. Effective chemical additives include chlorine, chlorine dioxide, iodine, and sodium hypochlorite (bleach).
[edit] Chemical disinfection
Iodine is added to water as a solution, crystallised, 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 light weight solution for those in need of field purification of drinking water. There are kits available in camping stores that include an iodine pill and a second pill that will remove the iodine taste from the water after it has been disinfected.
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 safe 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 drinking water disinfection.[1]
Neither chlorine (e.g. bleach) nor iodine alone is considered effective against Cryptosporidium, and they are limited in effectiveness against Giardia. Chlorine is slightly better than iodine against Giardia.
[edit] Solar distillation
In SODIS (Solar Water Disinfection) 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 any microbes that may be present. The combination of the two provides a simple method of disinfection for tropical developing countries.
[edit] Prevention of water contamination
To help minimise problems with drinking water in wilderness areas, it is strongly recommended that all waste is packed up and carted out to a properly designated disposal point. Burying human waste, even away from a watercourse may be storing up serious problems for the next visitors to the area and also potentially to the local animal population.
[edit] See also
- Water purification – large-scale methods
- Potability of backcountry water
- Appropriate technology#Water treatment – Water treatment section of Appropriate technology article.
[edit] References
- ^ The product is sold in Indonesia as Air RahMat. Aman Tirta (Safe Water Systems), from the Johns Hopkins Bloomberg School of Public Health's Center for Communication Programs site; U.S. Embassy Press Release February 28, 2006
