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, odors, and heavy metals like lead and mercury.
Iodine 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-rations 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
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.
Ultraviolet (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 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. 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.
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.
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, odors, and heavy metals like lead and mercury.
Iodine 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-rations 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
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.
Ultraviolet (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 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. 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.
