Water Purification Tablets: Used by survivalists, campers etc. Generally contains iodine or 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. 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.
A potentially lower cost alternative to using iodine-based water purification tablets is the use of iodine crystals. A small amount of water is poured into a small glass bottle (with a capacity of approximately 1 ounce or 30 cubic centimeters), containing approximately 0.25 ounces (7 grams) of iodine crystals, and then shaken vigorously to produce a saturated solution of iodine. At 25 °C (77 °F), 12.5 cubic centimeters of this solution is added to one liter of water to be disinfected. In 15 minutes the water may be consumed. At a temperature of 20 °C (68 °F) let the water to be consumed stand for 20 minutes. At a temperature of 3 °C (37 °F) let the water stand for 30 minutes or use 25 cubic centimeters of saturated solution per liter. (Do not store the saturated iodine solution in a plastic bottle as the iodine vapor will pass through the plastic and corrode steel that is in close proximity.) Note also that this method may not be adequate in killing Giardia cysts in cold water. One solution is to warm the water to be consumed to 20 °C (68 °F) before treatment. Take care not to consume iodine crystals; the amount of iodine in the saturated solution may be two to four times the lethal dose. Care must be taken to prevent the small glass bottle of iodine crystals covered with water from freezing in cold climates. 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. 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.
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 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, typically 3 days or less, unlike iodine-based tablets which have a usable open bottle life of 3 months. Sodium dichloroisocyanurate (NaDCC) has largely displaced halazone tablets for the few remaining chlorine based water purification tablets available today. It 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 halazone tablets falling from favor for portable water purification, 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 against the latter. A more complete field solution that includes chemical disinfectants is to first filter the water, using a 0.2 µm 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.
A potentially lower cost alternative to using iodine-based water purification tablets is the use of iodine crystals. A small amount of water is poured into a small glass bottle (with a capacity of approximately 1 ounce or 30 cubic centimeters), containing approximately 0.25 ounces (7 grams) of iodine crystals, and then shaken vigorously to produce a saturated solution of iodine. At 25 °C (77 °F), 12.5 cubic centimeters of this solution is added to one liter of water to be disinfected. In 15 minutes the water may be consumed. At a temperature of 20 °C (68 °F) let the water to be consumed stand for 20 minutes. At a temperature of 3 °C (37 °F) let the water stand for 30 minutes or use 25 cubic centimeters of saturated solution per liter. (Do not store the saturated iodine solution in a plastic bottle as the iodine vapor will pass through the plastic and corrode steel that is in close proximity.) Note also that this method may not be adequate in killing Giardia cysts in cold water. One solution is to warm the water to be consumed to 20 °C (68 °F) before treatment. Take care not to consume iodine crystals; the amount of iodine in the saturated solution may be two to four times the lethal dose. Care must be taken to prevent the small glass bottle of iodine crystals covered with water from freezing in cold climates. 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. 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.
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 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, typically 3 days or less, unlike iodine-based tablets which have a usable open bottle life of 3 months. Sodium dichloroisocyanurate (NaDCC) has largely displaced halazone tablets for the few remaining chlorine based water purification tablets available today. It 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 halazone tablets falling from favor for portable water purification, 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 against the latter. A more complete field solution that includes chemical disinfectants is to first filter the water, using a 0.2 µm 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.
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