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Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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In the Wake of Hurricane Irene – Methods of Water Disinfection

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A store in New York city, boarded up in preparation for Hurricane Irene. Photo courtesy of David Shankbone (CC BY 3.0) A store in New York city, boarded up in preparation for Hurricane Irene. Photo courtesy of David Shankbone (CC BY 3.0)In the wake of Hurricane Irene, many people will be without electrical power for days. If they need to disinfect water to obtain drinking water, the following are some techniques that may be used:

Water disinfection is the treatment of water with chemicals, boiling, or filtration in order to remove agents of infectious disease, such as bacteria and cysts. The principal offending agents in contaminated water or on unwashed food that cause illness and diarrhea are the bacteria Salmonella, Shigella, E. coli, and Campylobacter, and the flagellate protozoan Giardia lamblia

All containers should be wiped clean to remove external moisture and dirt. If the water to be disinfected is cloudy or dirty, it should be allowed to rest for several hours in order for large particles to settle to the bottom. The top portion can be poured off—if possible, it should be poured through a filter or fine cloth. 

Coagulation and flocculation techniques can remove smaller suspended particles: Add a pinch of alum (an aluminum salt) to a gallon (3.8 liters) of water and mix well, then stir occasionally for 60 minutes. Allow the water to rest while the aggregated particles settle, then pour off the upper (and hopefully clearer) part through a paper filter (such as a laboratory-grade filter with a pore size of 20 to 30 microns).

Water may be disinfected by any of the following methods:

1. Boil the water.

At sea level, when water has been boiled for a few minutes, it can be considered to have been disinfected. Giardia cysts are instantly killed in water heated to 158° F (70° C). To play it safe, keep boiling it for a few minutes at this temperature to kill off all bacteria and most viruses. Hepatitis A virus requires a full minute of boiling to assure inactivation. To provide a wide margin of safety, boil the water for three minutes. 

Time and temperature have an inverse relationship with respect to water disinfection: The higher the temperature, the less time is required, and vice versa. For instance, pasteurization of food products can occur at a lower temperature (158° F, or 70° C) if 30 minutes at this temperature are allowed. Sterilization (killing of all microorganisms) occurs after five to 10 minutes of boiling at sea level.

2. Use a halogen, such as iodine or chlorine, as a chemical disinfectant.

The rate at which halogens kill microorganisms depends upon the concentration (measured in mg per liter, or parts per million [ppm], which are equivalent) of halogen and time allowed for disinfection. At a given water temperature and pH, contact time is inversely related to concentration. Thus, you double the contact time if half the concentration of halogen is present. Decreased (cold) water temperature or cloudy (more organic material) water requires a longer contact time or higher halogen concentration. Halogens can create an unpleasant taste if the concentration exceeds four mg/liter. They can lose effectiveness after prolonged exposure to moisture, heat, or air, and may be corrosive or stain clothing. In general, to improve taste, use a lower concentration of halogen for a longer contact time. Eight mg/liter (or ppm) is considered the concentration of iodine effective for water disinfection in room-temperature, clear water. A pregnant woman or a person with thyroid disease or iodine allergy should consult a physician before using any iodine compound for water disinfection.

Water disinfection tablets, such as Potable Aqua® (see below) and other iodine- and chlorine-based products may be used inside plastic hydration bladders, such as those found in the CamelBak®. While they may discolor the plastic, they do not degrade it. 

Add one tablet of fresh tetraglycine hydroperiodide (Potable Aqua®, Globaline, Coughlan’s, EDWGT) to one quart (liter) of water and allow the water to stand for 15 minutes. If the water is cloudy, use two tablets. If the water is cold, allow one hour after adding the tablets before drinking. Each tablet releases approximately 8 mg/liter of iodine. Do not leave an open bottle exposed to high heat and/or humidity. Potable Aqua Plus includes oxidizing tablets to remove the iodine taste after disinfection. 

Add to 1 quart (liter) of water: 

water

clear

cloudy

warm (>15° C, 59° F)          

1 tab for 15 minutes           

2 tabs for 30 minutes

cold

1 tab for 60 minutes

2 tabs for 60 minutes

After adequate time for disinfection has elapsed, add a few grains of sodium thiosulfate per quart (liter) of water; this kills the iodine taste. Ascorbic acid (vitamin C) is also effective. Any fruit flavorings that contain vitamin C should be mixed in after full time for disinfection has elapsed. Granular activated charcoal removes organic material, chemicals, and radioactive particles by adsorption, but does not remove all microorganisms, and thus cannot be relied upon to disinfect water. Rather, it should be used to improve taste and clarity. Use it after water has been properly disinfected.

Zinc metal reduces free chlorine or iodine in solution through a chemical reaction. A wand of zinc bristles stirred into a quart (liter) of water for 4 minutes will remove 10 mg/liter of residual chlorine. 

Because a 50-tablet bottle of tetraglycine hydroperiodide contains only 0.4 g of iodine (1/50 the lethal dose), the tablet method is very safe. If you use military surplus iodine tablets, they should be steel gray in color and not crumble when pinched by two fingers; discard older, crumbled tablets. Also, no matter what chemical disinfection system you use, allow disinfected water to seep around the cap and threads of your canteen or water bottle, in order to disinfect them. 

Another method is to add 8 to 10 drops (0.5 ml in each drop) of standard 2 percent iodine tincture per quart (liter) of water and allow it to stand for 15 minutes. Use a dropper for measurement. If the water is not at least 68° F (20° C), this technique may not eliminate Giardia. If the water is cold, allow it to stand for 1 hour before drinking. If you have extra time and do not like the iodine taste, use four to five drops of iodine and allow the water to stand for 8 hours or overnight. Five drops of tincture of iodine disperses to approximately 4 mg/liter. 

add to 1 quart (liter) of water:

water

   clear

cloudy

warm (>15° C, 59° F)    

5 drops for 15 minutes

10 drops for 30 minutes

cold

5 drops for 60 minutes

10 drops for 60 minutes

Another iodine product that can be used to disinfect water, but has not definitively been proven effective for this purpose, is 10 percent povidone iodine (Betadine) solution (not “scrub”): 

add to 1 quart (liter) of water:

water

   clear

cloudy

warm (>15° C, 59° F)    

8 drops for 15 minutes

16 drops for 30 minutes

cold

8 drops for 60 minutes

16 drops for 60 minutes 

Another method is to fill a 1 oz (30 ml) glass bottle with iodine crystals (U.S. Pharmacopoeia [USP] grade, resublimed: 2 to 8 grams), then fill the bottle with water. The bottle should have a paper-lined Bakelite cap. Warm the water to 68 to 77° F (20 to 25° C). Shake vigorously, then allow the crystals to settle to the bottom for 1 hour. This will create a saturated solution of iodine. As a crude measure, pour at least half of this liquid (not the remaining crystals), or approximately 12.5 to 15 ml, through a fine filter (such as Teflon) into a quart (liter) of water and allow it to stand for 30 minutes. If the water temperature is not at least 68° F (20° C), this technique may not eliminate Giardia. The crystals may be reused up to 1,000 times. Two grams (0.07 oz) of iodine represents a potentially lethal dose if ingested, so it is absolutely essential to keep the iodine crystals out of the hands of children. A commercial iodine crystal system that can be reused to disinfect up to 2,000 quarts (liters) of drinking water is sold as Polar Pure Water Disinfectant.

If one capful from a 2 oz (59 ml) bottle equals approximately 2.5 ml, then using a saturated solution prepared from iodine crystals in water: 

add to 1 quart (liter) of water:

water

     clear

cloudy

warm (>15° C, 59° F)     

5 capfuls for 15 minutes

10 capfuls for 30 minutes

cold

5 capfuls for 60 minutes

10 capfuls for 60 minutes

An alcohol-iodine solution can be prepared by adding 8 g of iodine crystals to 100 ml of 95 percent ethanol. The resulting supernatant yields 8 mg iodine per 0.1 ml. To add to water, measure with an eyedropper:

add to 1 quart (liter) of water:

water

 clear

cloudy

warm (>15° C, 59° F)     

0.1 ml for 15 minutes

0.2 ml for 30 minutes

cold

0.1 ml for 60 minutes

0.2 ml for 60 minutes

3. Filter the water through a category-three (as set for purification by the Environmental Protection Agency) water treatment device. 

Manufacturers who sell representative devices are the Mountain Safety Research, Katadyn, AquaRain Filter Systems, General Ecology Inc.,  Recovery Engineering, Timberline, Stearns Outdoors Inc., McNett, and Sawyer Products. The Sawyer Point Zero Two™ water filter, with a 0.02 micron filter, is rated to remove viruses. This product is available with a bucket adapter kit, or can be fitted to four liter bags or a special water bottle.

If the filter ­doesn’t come with a “prefilter” (nylon mesh or screen) to remove large particles, pour the water through filter paper (like coffee filter paper) or fine cheesecloth. This helps keep your expensive water filter from clogging up, allows it to work more efficiently, and will improve the appearance and taste of the water.

4. Use halazone prodcuts to disinfect water.

Halazone (a mixture of monochloraminobenzoic and dichloramino­benzoic acids) or other chlorine (bleach) products have been considered less effective for field water disinfection. Halazone has been characterized as losing 75 percent of activity after two days’ continuous exposure to air with high heat and humidity; having a shelf life of six months; and decreasing potency by 50 percent after storage above 104° F (40° C). Therefore, you should obtain a new bottle every three to six months.

Each Halazone tablet releases 2.3 to 2.5 mg/liter of chlorine. To disinfect water:

add to 1 quart (liter) of water:

water

    clear

cloudy

warm (>15° C, 59° F)    

5 tablets for 15 minutes

2.5 tablets for 30 minutes

7 tablets for 15 minutes

5 tablets for 30 minutes

cold

5 tablets for 60 minutes

7 tablets for 60 minutes

Liquid bleach (hypochlorite solution; household bleach, usually 5.25 percent) can be used to disinfect water via chlorination. There should be a faint smell or taste of chlorine before drinking.

For 5.25 percent bleach, add to 1 quart (liter) of water:

water

clear

cloudy

warm (>15° C, 59° F)

2 drops (0.1 ml) for 30 minutes

4 drops (0.2 ml) for 30 minutes

cold

2 drops (0.1 ml) for 60 minutes

4 drops (0.2 ml) for 60 minutes

For 1 percent bleach, add to 1 quart (liter) of water:

water

clear

cloudy

warm (>15° C, 59° F)

10 drops (0.5 ml) for 30 minutes

20 drops (1 ml) for 30 minutes

cold

10 drops (0.5 ml) for 60 minutes

20 drops (1 ml) for 60 minutes

5. Superchlorination and dechlorination.

Superchlorination followed by dechlorination is an effective technique. This is a more complicated method that requires understanding and experience. Add 27 g or more of calcium hypochlorite crystals to a gallon (3.8 liters) of water to attain a chlorine concentration of 27 to 30 parts per million. After the requisite disinfection time (10 to 30 minutes), add six drops of concentrated (30 percent, caustic) hydrogen peroxide to dechlorinate the water. The chemical reaction produces calcium chloride (which remains in solution), water, and oxygen.

6. Aquamira® water treatment.

Aquamira® water treatment uses stabilized 2 percent chlorine dioxide combined with an activator (5 percent food grade phosphoric acid) to improve the taste of  water. One kit can be used to treat more than 120 liters of water. Mix 7 drops of the two bottles together, and let sit 5 minutes, then pour the contents into 1 quart of water.  Oxygen is released in a highly active form to kill odor-causing bacteria. The process takes approximately 20 minutes.

7. The SteriPEN™

The SteriPEN™  carries the promotional byline of “safe drinking water anywhere.” Distributed by Traveler’s Supply, Inc., this unique hand-held water purifier that uses ultraviolet light (UVL) is advertised to fit into most plastic consumer water bottles as well as other types of containers up to 32 ounces (1 liter). It operates on 4 AA batteries, with nickel-metal-hydride or lithium batteries recommended. According to the distributor, only 48 seconds of exposure to the UVL is required to disinfect 16 ounces (1/2 liter) of water and 90 seconds for 32 ounces (1 liter). The claim is that the device is effective against common outdoor and household pathogens, as well as less common micro-organisms, to include bacteria, viruses, and protozoa. The test results are found at an Internet link provided by the company. According to the product literature, the SteriPEN™ meets U.S. Environmental Protection Agency standards for microbiological water purifiers. A filter can be used to remove particulates from the water prior to UV treatment.

UVL works for water disinfection by destroying the DNA of microbes. This keeps the germs from reproducing, which is necessary in order for them to make a person ill. The light emitted by the SteriPEN™ device is in the UV-C range, of wavelength 254 nanometers. This wavelength is germicidal (kills germs) by causing adjacent thymine base nucleotides in DNA to bond together, which prevents them from being properly recognized (“read”) in the replication process, which is necessary for DNA to allow a micro-organism to reproduce. Thus, the germ(s) is rendered harmless. Used as directed, the UVL exposure is of no consequence, as this wavelength of UVL does not pass through most materials (e.g., glass, metal, ceramic, and nearly all plastics). Furthermore, the underside of the air/water surface in a water container acts as a reflector for UV-C. So, if the SteriPEN™ lamp is completely immersed in water and used according to the instructions, the UV-C is contained and does not pose any health risk to the user. For additional safety, the SteriPEN is equipped with water sensors and will not operate unless the lamp is under water. The SteriPEN™ contains a microcomputer that controls operation time, according to information it receives from integrated temperature sensors and user indication of the volume of water to be disinfected. During use, the device should be used to gently stir the water. It is intended for use in clear water, so cloudy water must be filtered or otherwise made clear prior to using the SteriPEN™. Disposable lithium or rechargeable AA nickel metal hydride batteries will provide many more disinfection cycles than will alkaline batteries. The latter are better in a cold weather situation.

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Tags: Humanitarian Care , Products , Staying Safe

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About the Author

Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.

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