Portable water purification
Encyclopedia
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, survivalists, and others 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 (that is, safe and palatable for drinking purposes).
Many commercial portable water purification systems or chemical additives are available for hiking, camping, and other travel in remote areas. These devices are not only used for remote or rural areas, but also to treat safe municipal water
for aesthetic purposes by removing chlorine
, bad taste, odor
s, and heavy metals like lead
and mercury
.
Large rivers may be polluted with sewage effluent
, surface runoff
, or industrial pollutants
from sources far upstream. However, even small stream
s, springs
and wells
may be contaminated by animal waste and pathogen
s. The presence of dead animals upstream is not uncommon. In most parts of the world, water may be contaminated by bacteria, protozoa
or parasitic worms from human and animal waste or pathogens which use other organisms as an intermediate host. Pathogenic strains of E coli
bacteria survive briefly outside the body, to infect new hosts.
Giardia lamblia
and Cryptosporidium
spp., both of which cause diarrhea
(see giardiasis
and cryptosporidiosis
) are common pathogens. In backcountry areas of the United States
and Canada
they are sometimes present in sufficient quantity that water treatment is justified for backpackers, although this has created some controversy. (See Wilderness acquired diarrhea.) In Hawaii
and other tropical areas, Leptospira
spp. are another possible problem.
Less commonly seen 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 flukes
are particularly dangerous in area frequented by sheep, deer
, or cattle
. If such 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
.
, as regular boiling will not heat water past 100 °C (212 °F) at sea level. It is worth noting that not all pollutants are removed from water by boiling, even in a pressure cooker. Boiling cannot remove chemicals having boiling points at or above 100 °C (212 °F), nor heavy metal contamination, e.g., colloidal metal pollutants. Activated charcoal
, however, can remove many pollutants, but can't remove pathogens. A combination of rolling boiling for one minute at standard atmospheric pressure (i.e., not in a pressure cooker) plus filtering with activated charcoal can neutralize most pathogens and pollutants.
(µm) range. Some also utilize activated charcoal filtering. Most filters of this kind remove most bacteria and protozoa, such as Cryptosporidium and Giardia lamblia, but not viruses except for the very largest of 0.3 micrometer and larger diameters, so disinfection by chemicals or ultraviolet light
is still required after filtration. It is worth noting that not all bacteria are removed by 0.2 micron (micrometer) pump filters; for example, strands of thread-like Leptospira spp. bacteria, (that can cause leptospirosis), are thin enough to pass through a 0.2 micrometer filter. Effective chemical additives to address shortcomings in pump filters 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 and the smaller bacteria that cannot be filtered out, 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.
While the filtration elements may do an excellent job of removing most 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.
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.
A new portable pump filter, the LifeSaver bottle, filters with a combination of hand pump, filter membranes
and a charcoal filter. This new system removes particles larger than 15 nm, and thus is able to filter-out viruses. A similar system, the LifeStraw
, removes particles larger than 0.2 microns using hollow fiber membrane technology.
many compounds, including many toxic
compounds. Water passing through activated carbon is commonly used in concert with hand pumped filters to address organic contamination
, taste, or objectionable odors. Activated carbon filters aren't usually used as the primary purification techniques of portable water purification devices, but rather as secondary means to complement another purification technique. It is most commonly implemented for pre-filtering or post-filtering, in a separate step than ceramic filtering, in either case being implemented prior to the addition of chemical disinfectants used to control bacteria or viruses that filters cannot remove. Activated charcoal can remove chlorine from treated water, removing any residual protection remaining in the water protecting against pathogens, and should not, in general, be used without careful thought after chemical disinfection treatments in portable water purification processing.
used for water purification is commonly added to water as a solution, in crystallized form, or in tablets containing tetraglycine hydroperiodide that release 8 mg of iodine per tablet adaptation to chronic tetraglycine hydroperiodide. 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, such as those marketed under the Potable Aqua Plus name. The addition of vitamin C, in the form of a pill or in flavored drink powders, precipitates much of the iodine out of solution, so it should not be added until the 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. Iodine treated drinking water, treated with tablets containing tetraglycine hydroperiodide, also reduces the uptake of radioactive iodine in human subjects to only 2% of the value it would otherwise be., This could be an important factor worthy of consideration for treating water in a post nuclear event survival situation. If the iodine has precipitated out of the solution, then drinking the water has less available iodine in solution. Also the amount of iodine in one tablet is not sufficient to block uptake. Such iodine treated water is not suitable for the small percentage of the population allergic to iodine, a problem that also exists in using iodine-based dyes for medical test radiography
imaging. Tetraglycine hydroperiodide maintains its effectiveness indefinitely before the container is opened; although some manufacturers suggest not using the tablets more than three months after they the container has initially been opened, the shelf life is in fact very long provided that the container is resealed immediately after each time it is opened.
A potentially lower cost alternative to using iodine based water purification tablets is the use of iodine crystals, commonly sold under the Polar Pure name. A small amount of water is poured into a small glass bottle containing 0.25 ounces of iodine crystals, shakes and waits 60 minutes, and then pours off only the amount of liquid solution needed into a larger source of untreated water such as a canteen. After waiting 20 minutes, lengthened if treating cold water instead of warm water, potable water is then available from the treated water. An advantage of using iodine crystals is that only a small amount of iodine is dissolved from the iodine crystals at each use, giving this method of treating water a capability for treating very large amounts of water, around 2,000 liters (500 gallons), with but a small bottle of crystals. Ingestion of the actual iodine crystals must be avoided when using this method. Unlike tetraglycine hydroperiodide tablets, iodine crystals have essentially an unlimited shelf life as long as they are not exposed to air for long periods of time and are kept under water. (Iodine crystals will sublimate if exposed to air for long periods of time.) The large quantity of water that can be purified with iodine crystals at low cost makes this technique especially cost effective for point of use or emergency water purification methods intended for use longer than the shelf life of tetraglycine hydroperiodide. Care must be taken to prevent the small glass bottle of iodine crystals covered with water from freezing in cold climates.
Chlorine-based halazone tablets were formerly popularly used for portable water purification. Chlorine in water is more than three times more effective as a disinfectant against Escherichia coli
than an equivalent concentration of iodine
. Halazone tablets were thus commonly used during World War II
by U.S. soldiers for portable water purification, even being included in accessory packs for C-ration
s until 1945. The primary limitation of halazone tablets was the very short usable life of opened bottles of halazone tablets, typically 3 days or less, unlike iodine based tablets which have a usable open bottle life of 3 months. Sodium dichloroisocyanurate
has largely displaced halazone tablets for the few remaining chlorine based water purification tablets available today. Sodium dichloroisocyanurate is often abbreviated to NaDCC and is compressed with effervescent salts, usually adipic acid
and sodium bicarbonate
to form a rapidly dissolving tablets. Diluted to 10 parts per million available chlorine (ppm av.cl) when drinking water is mildly contaminated
and 20ppm when visibly contaminated. Chlorine bleach tablets give a more stable platform for disinfecting the water than liquid bleach
(sodium hypochlorite) as the liquid version tends to degrade with age and give unregulated results unless assays are carried out not practical on the spot. Still, despite chlorine-based portable water purification falling from favor in tablet form such as in halazone tablets, chlorine-based bleach may nonetheless safely be used for short term emergency water disinfection. Two drops of unscented 5% bleach can be added per liter or quart of clear water, then allowed to stand covered for 30 to 60 minutes. After this treatment, the water may be left open to reduce the chlorine smell and taste. Guidelines are available online for effective emergency use of bleach to render unsafe water potable. The Centers for Disease Control & Prevention (CDC) and Population Services International (PSI) promote a similar product (a 0.5% - 1.5% sodium hypochlorite solution) as part of their Safe Water System (SWS) strategy. The product is sold in developing countries under local brand names specifically for the purpose of disinfecting drinking water (CDC: SWSPSI: SWS).
Neither chlorine (e.g., bleach) nor iodine alone is considered completely effective against Cryptosporidium
, although they are partially effective against Giardia
. Iodine should be allowed at least 30 minutes to kill Giardia. Chlorine is considered slightly better than iodine against Giardia. A more complete field solution that includes chemical disinfectants is to first filter the water, using a 0.2 micron ceramic cartridge pumped filter, followed by treatment with iodine or chlorine, thereby filtering out cryptosporidium, Giardia, and most bacteria, along with the larger viruses, while also using chemical disinfectant to address smaller viruses and bacteria that the filter cannot remove. This combination is also potentially more effective in some cases than even using portable electronic disinfection based on UV treatment, such as using a SteriPEN uv portable water purifier.
An alternative to iodine based preparations in some usage scenarios are silver
ion/chlorine dioxide
based tablets or droplets. Sold under names like Micropur Forte, Aquamira, and Pristine, these solutions may disinfect water more effectively than iodine based techniques while leaving hardly any noticeable taste in the water in some usage scenarios. Silver ion/chlorine dioxide based disinfecting agents will kill Cryptosporidum and Giardia, if utilized correctly. The primary disadvantage of silver ion/chlorine dioxide based techniques is the long purification times (generally 30 minutes to 4 hours, depending on the formulation used). Another concern is the possible deposition and accumulation of silver compounds in various body tissues leading to a rare condition called argyria
that results in a permanent, disfiguring, bluish-gray pigmentation of the skin, eyes, and mucous membranes. The cost of chlorine dioxide treatment is about four times higher than the cost of iodine treatment.
(UV) light induces the formation of covalent linkages on DNA
and thereby prevents microbes from reproducing. Without reproduction, the microbes become far less dangerous. Germicidal UV-C light in the short wavelength range of 100–280 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 SteriPEN. These UV water purifiers are lightweight and work very quickly. Still, there are limits to this technology. Water turbidity (i.e., the amount of suspended & colloidal solids contained in the water to be treated) must be low, such that the water is clear, for UV purification to work well. Also, water treated with UV still has the microbes present in the water, only with their means for reproduction turned "off". In the event that such UV-treated water containing neutered microbes is exposed to visible light (specifically, wavelengths of light over 330-500 nm) for any significant period of time, a process known as photoreactivation
can take place, whereby there becomes a possibility for repairing the damage in the bacteria's reproduction DNA, potentially rendering them once more capable of reproducing and causing disease. UV-treated water must therefore not be exposed to visible light for any significant period of time after UV treatment, before consumption, to avoid ingesting reactivated and dangerous microbes. For long term usage, the issue of obtaining batteries to power portable water purification UV devices can be a concern.
Another concern with UV portable water purification is that some pathogens are hundreds of times less sensitive to UV light than others. Protozoan cysts were once believed to be among the least sensitive, however recent studies have proved otherwise, demonstrating that both Cryptosporidium and Giardia are deactivated by a UV dose of just 6 mJ/cm sq. However, EPA regulations and other studies show that it is viruses that are the limiting factor of UV treatment, requiring a 10-30 times greater dose of UV light than Giardia or Cryptosporidium
. Furthermore, studies have shown that UV doses at the levels provided by common portable UV units are effective at killing Giardia and that there was no evidence of repair and reactivation of the cysts.
Fortunately, Giardia are among the easiest pathogens to filter out of water. A viable two-step portable water purification approach, providing greater protection than UV purification alone, is to first filter suspect water, thereby removing the larger pathogens, prior to using UV purification.
. Water is placed in a transparent plastic PET
bottles, which is first oxygenated by shaking partially-filled capped bottles prior to filling the bottles all the way. The completely water-filled and capped bottles are exposed to sunlight, preferably on a corrugated metal roof, slanted slightly to maximize the exposure to solar radiation. In practice, the water-filled bottles are placed for six hours in full sun, or for two days in partial sunlight for weather conditions involving partially overcast days, which raises the temperature of the water and gives an extended dose of solar radiation to the water in the bottles, killing almost all microbes that may be present. The combination of the two effects (UVA and heat) provides a simple method of disinfection for use in tropical developing countries, or in survival situations. The use of glass bottles may or may not provide the same degree of SODIS disinfection as using PET bottles. This is because most glass bottles are non-transparent or opaque over the wavelengths of sunlight required for successful UV disinfection from the solar spectrum required for SODIS to work, and glass bottles are usually thicker than PET bottles, which further reduces the dose of UVA to the water inside glass bottles versus PET bottles. For cases where the UVA is blocked, or reduced, only the heating effects without adequate UVA exposure are typically at work if glass bottles are used, potentially leaving dangerous amounts of bacterial and viral loads within the water.
Water filters can be made on-site using local materials such as grass, charcoal
(e.g. from firewood burned in a special way). These filters are often used by soldiers and outdoor enthusiasts. Due to their low cost they can be made and used by anyone. Regrettably such filters do little, if anything, to mitigate germs and other harmful constituents and can give a false sense of security that the water so produced is potable. Water processed through improvised filters should be subsequently boiled to render it safe for consumption.
Drinking water
Drinking water or potable water is water pure enough to be consumed or used with low risk of immediate or long term harm. In most developed countries, the water supplied to households, commerce and industry is all of drinking water standard, even though only a very small proportion is actually...
from untreated sources (e.g., rivers, lakes, etc.). The objective of these personal devices is to render unchlorinated
Chlorination
Chlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water...
water potable (that is, safe and palatable for drinking purposes).
Many commercial portable water purification systems or chemical additives are available for hiking, camping, and other travel in remote areas. These devices are not only used for remote or rural areas, but also to treat safe municipal water
Water purification
Water purification is the process of removing undesirable chemicals, materials, and biological contaminants from contaminated water. The goal is to produce water fit for a specific purpose...
for aesthetic purposes by removing chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
, bad taste, odor
Odor
An odor or odour is caused by one or more volatilized chemical compounds, generally at a very low concentration, that humans or other animals perceive by the sense of olfaction. Odors are also commonly called scents, which can refer to both pleasant and unpleasant odors...
s, and heavy metals like lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
and mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
.
Drinking water hazards
Sewage treatment
Sewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...
, surface runoff
Surface runoff
Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...
, or industrial pollutants
Water pollution
Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....
from sources far upstream. However, even small stream
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
s, springs
Spring (hydrosphere)
A spring—also known as a rising or resurgence—is a component of the hydrosphere. Specifically, it is any natural situation where water flows to the surface of the earth from underground...
and wells
Water well
A water well is an excavation or structure created in the ground by digging, driving, boring or drilling to access groundwater in underground aquifers. The well water is drawn by an electric submersible pump, a trash pump, a vertical turbine pump, a handpump or a mechanical pump...
may be contaminated by animal waste and pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
s. The presence of dead animals upstream is not uncommon. In most parts of the world, water may be contaminated by bacteria, protozoa
Protozoa
Protozoa are a diverse group of single-cells eukaryotic organisms, many of which are motile. Throughout history, protozoa have been defined as single-cell protists with animal-like behavior, e.g., movement...
or parasitic worms from human and animal waste or pathogens which use other organisms as an intermediate host. Pathogenic strains of E coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
bacteria survive briefly outside the body, to infect new hosts.
Giardia lamblia
Giardia lamblia
Giardia lamblia is a flagellated protozoan parasite that colonizes and reproduces in the small intestine, causing giardiasis. The giardia parasite attaches to the epithelium by a ventral adhesive disc, and reproduces via binary fission...
and Cryptosporidium
Cryptosporidium
Cryptosporidium is a protozoan that can cause gastro-intestinal illness with diarrhea in humans.Cryptosporidium is the organism most commonly isolated in HIV positive patients presenting with diarrhea...
spp., both of which cause diarrhea
Diarrhea
Diarrhea , also spelled diarrhoea, is the condition of having three or more loose or liquid bowel movements per day. It is a common cause of death in developing countries and the second most common cause of infant deaths worldwide. The loss of fluids through diarrhea can cause dehydration and...
(see giardiasis
Giardiasis
Giardiasis or beaver fever in humans is a diarrheal infection of the small intestine by a single-celled organism Giardia lamblia. Giardiasis occurs worldwide with a prevalence of 20–30% in developing countries. In the U.S., 20,000 cases are reported to the CDC annually, but the true annual...
and cryptosporidiosis
Cryptosporidiosis
Cryptosporidiosis, also known as crypto, is a parasitic disease caused by Cryptosporidium, a protozoan parasite in the phylum Apicomplexa. It affects the intestines of mammals and is typically an acute short-term infection...
) are common pathogens. In backcountry areas of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
and Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
they are sometimes present in sufficient quantity that water treatment is justified for backpackers, although this has created some controversy. (See Wilderness acquired diarrhea.) In Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
and other tropical areas, Leptospira
Leptospira
Leptospira is a genus of spirochaete bacteria, including a small number of pathogenic and saprophytic species...
spp. are another possible problem.
Less commonly seen in developed countries are organisms such as Vibrio cholerae
Vibrio cholerae
Vibrio cholerae is a Gram-negative, comma-shaped bacterium. Some strains of V. cholerae cause the disease cholera. V. cholerae is facultatively anaerobic and has a flagella at one cell pole. V...
which causes cholera
Cholera
Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Transmission occurs primarily by drinking or eating water or food that has been contaminated by the diarrhea of an infected person or the feces...
and various strains of Salmonella
Salmonella
Salmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions . They are chemoorganotrophs, obtaining their energy from oxidation and reduction...
which cause typhoid and para-typhoid diseases. Pathogenic virus
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
es may also be found in water. The larvae of flukes
Fasciola hepatica
Fasciola hepatica, also known as the common liver fluke or sheep liver fluke, is a parasitic flatworm of the class Trematoda, phylum Platyhelminthes that infects the livers of various mammals, including humans. The disease caused by the fluke is called fascioliasis . F...
are particularly dangerous in area frequented by sheep, deer
Deer
Deer are the ruminant mammals forming the family Cervidae. Species in the Cervidae family include white-tailed deer, elk, moose, red deer, reindeer, fallow deer, roe deer and chital. Male deer of all species and female reindeer grow and shed new antlers each year...
, or cattle
Cattle
Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
. If such microscopic
Microscope
A microscope is an instrument used to see objects that are too small for the naked eye. The science of investigating small objects using such an instrument is called microscopy...
larvae are ingested, they can form potentially life threatening cyst
Cyst
A cyst is a closed sac, having a distinct membrane and division on the nearby tissue. It may contain air, fluids, or semi-solid material. A collection of pus is called an abscess, not a cyst. Once formed, a cyst could go away on its own or may have to be removed through surgery.- Locations :* Acne...
s in the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
or liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
. This risk extends to plants grown in or near water including the commonly eaten watercress
Watercress
Watercresses are fast-growing, aquatic or semi-aquatic, perennial plants native from Europe to central Asia, and one of the oldest known leaf vegetables consumed by human beings...
.
Techniques
Boiling
Boiling water will kill bacteria as well as other disease-causing microorganisms like Giardia lamblia and Cryptosporidium parvum 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 (158 °F) will kill all pathogens within 30 minutes, above 85 °C (185 °F) within a few minutes, and at boiling point (100 °C (212 °F)), most pathogens will be killed, excluding certain pathogens and their spores, which must be heated to 118 °C (244.4 °F)(e.g.: botulism Clostridium botulinum). This can be achieved by using a pressure cookerPressure cooking
Pressure cooking is a method of cooking in a sealed vessel that does not permit air or liquids to escape below a preset pressure. Because the boiling point of water increases as the pressure increases, the pressure built up inside the cooker allows the liquid in the pot to rise to a higher...
, as regular boiling will not heat water past 100 °C (212 °F) at sea level. It is worth noting that not all pollutants are removed from water by boiling, even in a pressure cooker. Boiling cannot remove chemicals having boiling points at or above 100 °C (212 °F), nor heavy metal contamination, e.g., colloidal metal pollutants. Activated charcoal
Activated carbon
Activated carbon, also called activated charcoal, activated coal or carbo activatus, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions.The word activated in the name is sometimes replaced...
, however, can remove many pollutants, but can't remove pathogens. A combination of rolling boiling for one minute at standard atmospheric pressure (i.e., not in a pressure cooker) plus filtering with activated charcoal can neutralize most pathogens and pollutants.
Filtration
Portable pump filters are commercially available with ceramic filters that filter 5,000 to 50,000 litres per cartridge, removing pathogens down to the 0.2–0.3 micrometerMicrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
(µm) range. Some also utilize activated charcoal filtering. Most filters of this kind remove most bacteria and protozoa, such as Cryptosporidium and Giardia lamblia, but not viruses except for the very largest of 0.3 micrometer and larger diameters, so disinfection by chemicals or ultraviolet light
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
is still required after filtration. It is worth noting that not all bacteria are removed by 0.2 micron (micrometer) pump filters; for example, strands of thread-like Leptospira spp. bacteria, (that can cause leptospirosis), are thin enough to pass through a 0.2 micrometer filter. Effective chemical additives to address shortcomings in pump filters 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 and the smaller bacteria that cannot be filtered out, 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.
While the filtration elements may do an excellent job of removing most 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.
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
Grease gun (tool)
A grease gun is a common workshop and garage tool used for lubrication. The purpose of the grease gun is to apply lubricant through an aperture to a specific point, usually on a grease fitting. The channels behind the grease nipple lead to where the lubrication is needed. The aperture may be of a...
. These devices can generate drinkable water from seawater.
A new portable pump filter, the LifeSaver bottle, filters with a combination of hand pump, filter membranes
Membrane technology
The membrane technology covers all process engineering measures for the transport of substances between two fractions with the help of permeable membranes...
and a charcoal filter. This new system removes particles larger than 15 nm, and thus is able to filter-out viruses. A similar system, the LifeStraw
LifeStraw
LifeStraw is a water filter designed to be used by one person to filter water so that they may safely drink it. It filters a maximum of 1000 litres of water, enough for one person for one year. It removes 99.9999% of waterborne bacteria and 99.9% of parasites...
, removes particles larger than 0.2 microns using hollow fiber membrane technology.
Activated charcoal absorption
Granular activated carbon filtering utilizes a form of activated carbon with a high surface area, and absorbsAbsorption
Absorption may refer to:- Chemistry and biology :* Absorption , absorption of particles of gas or liquid in liquid or solid material* Absorption , a route by which substances can enter the body through the skin...
many compounds, including many toxic
Toxicity
Toxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...
compounds. Water passing through activated carbon is commonly used in concert with hand pumped filters to address organic contamination
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
, taste, or objectionable odors. Activated carbon filters aren't usually used as the primary purification techniques of portable water purification devices, but rather as secondary means to complement another purification technique. It is most commonly implemented for pre-filtering or post-filtering, in a separate step than ceramic filtering, in either case being implemented prior to the addition of chemical disinfectants used to control bacteria or viruses that filters cannot remove. Activated charcoal can remove chlorine from treated water, removing any residual protection remaining in the water protecting against pathogens, and should not, in general, be used without careful thought after chemical disinfection treatments in portable water purification processing.
Chemical disinfection
IodineIodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
used for water purification is commonly added to water as a solution, in crystallized form, or in tablets containing tetraglycine hydroperiodide that release 8 mg of iodine per tablet adaptation to chronic tetraglycine hydroperiodide. 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
Ascorbic acid
Ascorbic acid is a naturally occurring organic compound with antioxidant properties. It is a white solid, but impure samples can appear yellowish. It dissolves well in water to give mildly acidic solutions. Ascorbic acid is one form of vitamin C. The name is derived from a- and scorbutus , the...
) that will remove the iodine taste from the water after it has been disinfected, such as those marketed under the Potable Aqua Plus name. The addition of vitamin C, in the form of a pill or in flavored drink powders, precipitates much of the iodine out of solution, so it should not be added until the 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
Turbidity
Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....
or cold. Iodine treated drinking water, treated with tablets containing tetraglycine hydroperiodide, also reduces the uptake of radioactive iodine in human subjects to only 2% of the value it would otherwise be., This could be an important factor worthy of consideration for treating water in a post nuclear event survival situation. If the iodine has precipitated out of the solution, then drinking the water has less available iodine in solution. Also the amount of iodine in one tablet is not sufficient to block uptake. Such iodine treated water is not suitable for the small percentage of the population allergic to iodine, a problem that also exists in using iodine-based dyes for medical test radiography
Radiography
Radiography is the use of X-rays to view a non-uniformly composed material such as the human body. By using the physical properties of the ray an image can be developed which displays areas of different density and composition....
imaging. Tetraglycine hydroperiodide maintains its effectiveness indefinitely before the container is opened; although some manufacturers suggest not using the tablets more than three months after they the container has initially been opened, the shelf life is in fact very long provided that the container is resealed immediately after each time it is opened.
A potentially lower cost alternative to using iodine based water purification tablets is the use of iodine crystals, commonly sold under the Polar Pure name. A small amount of water is poured into a small glass bottle containing 0.25 ounces of iodine crystals, shakes and waits 60 minutes, and then pours off only the amount of liquid solution needed into a larger source of untreated water such as a canteen. After waiting 20 minutes, lengthened if treating cold water instead of warm water, potable water is then available from the treated water. An advantage of using iodine crystals is that only a small amount of iodine is dissolved from the iodine crystals at each use, giving this method of treating water a capability for treating very large amounts of water, around 2,000 liters (500 gallons), with but a small bottle of crystals. Ingestion of the actual iodine crystals must be avoided when using this method. Unlike tetraglycine hydroperiodide tablets, iodine crystals have essentially an unlimited shelf life as long as they are not exposed to air for long periods of time and are kept under water. (Iodine crystals will sublimate if exposed to air for long periods of time.) The large quantity of water that can be purified with iodine crystals at low cost makes this technique especially cost effective for point of use or emergency water purification methods intended for use longer than the shelf life of tetraglycine hydroperiodide. Care must be taken to prevent the small glass bottle of iodine crystals covered with water from freezing in cold climates.
Chlorine-based halazone tablets were formerly popularly used for portable water purification. Chlorine in water is more than three times more effective as a disinfectant against Escherichia coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
than an equivalent concentration of iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
. Halazone tablets were thus commonly used during World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
by U.S. soldiers for portable water purification, even being included in accessory packs for C-ration
C-ration
The C-Ration, or Type C ration, was an individual canned, pre-cooked, or prepared wet ration intended to be issued to U.S. military land forces when fresh food or packaged unprepared food prepared in mess halls or field kitchens was impractical or not available, and when a survival ration was...
s until 1945. The primary limitation of halazone tablets was the very short usable life of opened bottles of halazone tablets, typically 3 days or less, unlike iodine based tablets which have a usable open bottle life of 3 months. Sodium dichloroisocyanurate
Sodium Dichloroisocyanurate
Sodium dichloroisocyanurate is a chemical compound used as a disinfectant, biocide, industrial deodorant and detergent. It is found in some newer water purification tablets/filters. It is more efficient than formerly used halazone water disinfectant...
has largely displaced halazone tablets for the few remaining chlorine based water purification tablets available today. Sodium dichloroisocyanurate is often abbreviated to NaDCC and is compressed with effervescent salts, usually adipic acid
Adipic acid
Adipic acid is the organic compound with the formula 42. From the industrial perspective, it is the most important dicarboxylic acid: About 2.5 billion kilograms of this white crystalline powder are produced annually, mainly as a precursor for the production of nylon...
and sodium bicarbonate
Sodium bicarbonate
Sodium bicarbonate or sodium hydrogen carbonate is the chemical compound with the formula Na HCO3. Sodium bicarbonate is a white solid that is crystalline but often appears as a fine powder. It has a slightly salty, alkaline taste resembling that of washing soda . The natural mineral form is...
to form a rapidly dissolving tablets. Diluted to 10 parts per million available chlorine (ppm av.cl) when drinking water is mildly contaminated
Contamination
Contamination is the presence of a minor and unwanted constituent in material, physical body, natural environment, at a workplace, etc.-Specifics:"Contamination" also has more specific meanings in science:...
and 20ppm when visibly contaminated. Chlorine bleach tablets give a more stable platform for disinfecting the water than liquid bleach
Bleach
Bleach refers to a number of chemicals that remove color, whiten, or disinfect, often via oxidation. Common chemical bleaches include household chlorine bleach , lye, oxygen bleach , and bleaching powder...
(sodium hypochlorite) as the liquid version tends to degrade with age and give unregulated results unless assays are carried out not practical on the spot. Still, despite chlorine-based portable water purification falling from favor in tablet form such as in halazone tablets, chlorine-based bleach may nonetheless safely be used for short term emergency water disinfection. Two drops of unscented 5% bleach can be added per liter or quart of clear water, then allowed to stand covered for 30 to 60 minutes. After this treatment, the water may be left open to reduce the chlorine smell and taste. Guidelines are available online for effective emergency use of bleach to render unsafe water potable. The Centers for Disease Control & Prevention (CDC) and Population Services International (PSI) promote a similar product (a 0.5% - 1.5% sodium hypochlorite solution) as part of their Safe Water System (SWS) strategy. The product is sold in developing countries under local brand names specifically for the purpose of disinfecting drinking water (CDC: SWSPSI: SWS).
Neither chlorine (e.g., bleach) nor iodine alone is considered completely effective against Cryptosporidium
Cryptosporidium
Cryptosporidium is a protozoan that can cause gastro-intestinal illness with diarrhea in humans.Cryptosporidium is the organism most commonly isolated in HIV positive patients presenting with diarrhea...
, although they are partially effective against Giardia
Giardia
Giardia is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada in the supergroup "Excavata" that colonise and reproduce in the small intestines of several vertebrates, causing giardiasis, commonly known as Beaver fever...
. Iodine should be allowed at least 30 minutes to kill Giardia. Chlorine is considered slightly better than iodine against Giardia. A more complete field solution that includes chemical disinfectants is to first filter the water, using a 0.2 micron ceramic cartridge pumped filter, followed by treatment with iodine or chlorine, thereby filtering out cryptosporidium, Giardia, and most bacteria, along with the larger viruses, while also using chemical disinfectant to address smaller viruses and bacteria that the filter cannot remove. This combination is also potentially more effective in some cases than even using portable electronic disinfection based on UV treatment, such as using a SteriPEN uv portable water purifier.
An alternative to iodine based preparations in some usage scenarios are silver
Silver
Silver is a metallic chemical element with the chemical symbol Ag and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal...
ion/chlorine dioxide
Chlorine dioxide
Chlorine dioxide is a chemical compound with the formula ClO2. This yellowish-green gas crystallizes as bright orange crystals at −59 °C. As one of several oxides of chlorine, it is a potent and useful oxidizing agent used in water treatment and in bleaching....
based tablets or droplets. Sold under names like Micropur Forte, Aquamira, and Pristine, these solutions may disinfect water more effectively than iodine based techniques while leaving hardly any noticeable taste in the water in some usage scenarios. Silver ion/chlorine dioxide based disinfecting agents will kill Cryptosporidum and Giardia, if utilized correctly. The primary disadvantage of silver ion/chlorine dioxide based techniques is the long purification times (generally 30 minutes to 4 hours, depending on the formulation used). Another concern is the possible deposition and accumulation of silver compounds in various body tissues leading to a rare condition called argyria
Argyria
Argyria is a condition caused by improper exposure to chemical forms of the element silver, silver dust, or silver compounds. The most dramatic symptom of argyria is that the skin becomes blue or bluish-grey colored. Argyria may be found as generalized argyria or local argyria...
that results in a permanent, disfiguring, bluish-gray pigmentation of the skin, eyes, and mucous membranes. The cost of chlorine dioxide treatment is about four times higher than the cost of iodine treatment.
Ultraviolet purification
UltravioletUltraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
(UV) light induces the formation of covalent linkages on DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
and thereby prevents microbes from reproducing. Without reproduction, the microbes become far less dangerous. Germicidal UV-C light in the short wavelength range of 100–280 nm acts on thymine
Thymine
Thymine is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine is also known as 5-methyluracil, a pyrimidine nucleobase. As the name suggests, thymine may be derived by methylation of uracil at...
, one of the four base nucleotide
Nucleotide
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
s in DNA. When a germicidal UV photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
is absorbed by a thymine molecule that is adjacent to another thymine within the DNA strand, a covalent bond
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....
or dimer between the molecules is created. This thymine dimer prevents enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
s 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. Still, there are limits to this technology. Water turbidity (i.e., the amount of suspended & colloidal solids contained in the water to be treated) must be low, such that the water is clear, for UV purification to work well. Also, water treated with UV still has the microbes present in the water, only with their means for reproduction turned "off". In the event that such UV-treated water containing neutered microbes is exposed to visible light (specifically, wavelengths of light over 330-500 nm) for any significant period of time, a process known as photoreactivation
Photolyase
Photolyases are DNA repair enzymes that repair damage caused by exposure to ultraviolet light. This enzyme mechanism requires visible light, preferentially from the violet/blue end of the spectrum, and is known as photoreactivation....
can take place, whereby there becomes a possibility for repairing the damage in the bacteria's reproduction DNA, potentially rendering them once more capable of reproducing and causing disease. UV-treated water must therefore not be exposed to visible light for any significant period of time after UV treatment, before consumption, to avoid ingesting reactivated and dangerous microbes. For long term usage, the issue of obtaining batteries to power portable water purification UV devices can be a concern.
Another concern with UV portable water purification is that some pathogens are hundreds of times less sensitive to UV light than others. Protozoan cysts were once believed to be among the least sensitive, however recent studies have proved otherwise, demonstrating that both Cryptosporidium and Giardia are deactivated by a UV dose of just 6 mJ/cm sq. However, EPA regulations and other studies show that it is viruses that are the limiting factor of UV treatment, requiring a 10-30 times greater dose of UV light than Giardia or Cryptosporidium
. Furthermore, studies have shown that UV doses at the levels provided by common portable UV units are effective at killing Giardia and that there was no evidence of repair and reactivation of the cysts.
Fortunately, Giardia are among the easiest pathogens to filter out of water. A viable two-step portable water purification approach, providing greater protection than UV purification alone, is to first filter suspect water, thereby removing the larger pathogens, prior to using UV purification.
Solar water disinfection
In solar water disinfection (SODIS), microbes are destroyed by temperature and UVA radiation provided by the sunSun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
. Water is placed in a transparent plastic PET
Polyethylene terephthalate
Polyethylene terephthalate , commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination...
bottles, which is first oxygenated by shaking partially-filled capped bottles prior to filling the bottles all the way. The completely water-filled and capped bottles are exposed to sunlight, preferably on a corrugated metal roof, slanted slightly to maximize the exposure to solar radiation. In practice, the water-filled bottles are placed for six hours in full sun, or for two days in partial sunlight for weather conditions involving partially overcast days, which raises the temperature of the water and gives an extended dose of solar radiation to the water in the bottles, killing almost all microbes that may be present. The combination of the two effects (UVA and heat) provides a simple method of disinfection for use in tropical developing countries, or in survival situations. The use of glass bottles may or may not provide the same degree of SODIS disinfection as using PET bottles. This is because most glass bottles are non-transparent or opaque over the wavelengths of sunlight required for successful UV disinfection from the solar spectrum required for SODIS to work, and glass bottles are usually thicker than PET bottles, which further reduces the dose of UVA to the water inside glass bottles versus PET bottles. For cases where the UVA is blocked, or reduced, only the heating effects without adequate UVA exposure are typically at work if glass bottles are used, potentially leaving dangerous amounts of bacterial and viral loads within the water.
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, typically being placed over a small pit that is dug into the ground. 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 cup placed beneath its center. For more continuous use, thin tubing or a hose is sometimes routed into the collection cup beneath the inverted cone, permitting repeated removal of water without disturbing the inverted cone upon which water condenses. This is potentially an important method to prevent losing moisture to atmospheric air, such as can occur in the desert, if the inverted cone is removed each time distilled water is removed from the cup. An alternative method based on the same technique is to tie a plastic bag over a branch of vegetation, to capture water released by the vegetation during photosynthesis. Note that while the solar still shares exposure to UV and infra-red radiation with SODIS, along with the use of plastic materials (sheeting in place of a PET bottle), a solar still relies on a completely different mechanism for operation and the two methods should not be confused. In an extreme survival situation, a solar still can be used to prepare safe drinking water from usually unsuitable water sources, such as one's own urine, or even sea water.Homemade water filters
Charcoal
Charcoal is the dark grey residue consisting of carbon, and any remaining ash, obtained by removing water and other volatile constituents from animal and vegetation substances. Charcoal is usually produced by slow pyrolysis, the heating of wood or other substances in the absence of oxygen...
(e.g. from firewood burned in a special way). These filters are often used by soldiers and outdoor enthusiasts. Due to their low cost they can be made and used by anyone. Regrettably such filters do little, if anything, to mitigate germs and other harmful constituents and can give a false sense of security that the water so produced is potable. Water processed through improvised filters should be subsequently boiled to render it safe for consumption.
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. Bury human waste well away from existing campsites and water sources (about 70 adult steps) to prevent site & source contamination, & reduce self contamination.Further reading
- Mark W LeChevallier and Kwok-Keung Au (2004) Water Treatment and Pathogen Control. World Health Organization. Accessed 2010-04-13
See also
- DesalinationDesalinationDesalination, desalinization, or desalinisation refers to any of several processes that remove some amount of salt and other minerals from saline water...
- Traveler's diarrheaTraveler's diarrheaTraveler's diarrhea , is the most common illness affecting travelers. An estimated 10 million people—20% to 50% of international travelers—develop it annually. TD is defined as three or more unformed stools in 24 hours passed by a traveler, commonly accompanied by abdominal cramps, nausea, and...
- Water qualityWater qualityWater quality is the physical, chemical and biological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species and or to any human need or purpose. It is most frequently used by reference to a set of standards against which...
- Wilderness acquired diarrhea