Portable water purification
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There is often a need to be able to treat water in remote or rural locations 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 contaimnated 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 develoiped 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.
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.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).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 a light weight but imperfect 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. [#endnote_1 EPA], [#endnote_2 BC Health]
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.
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.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 animmal population.See also
- Water purification – large-scale methods
- Potability of backcountry water
- Appropriate technology – examples of portable water purification and water supply are discussed under Some appropriate technologies.
References
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