WATER DISINFECTION

Water purification is the removal of chemical pollutants by filtration through activated charcoal or active resin compounds. This usually improves the taste, but does not decrease the incidence of infectious disease, because microorganisms are not removed. Water disinfection is the treatment of water with chemicals, boiling, or filtration to remove agents of infectious disease, such as bacteria and cysts. Sterilization is the removal of all life forms.

If at all possible, carry disinfected water with you. If you must drink water from a stream or lake that you cannot disinfect, try to use small tributaries that descend at right angles to the main direction of valley drainage. Clean melted snow is of less risk than ice taken from the surface of a lake or stream. Most bacteria that cause diarrhea can survive for months in ice.

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 (see page 207). Drinking nondisinfected water in parts of Africa, India, and Pakistan can cause dracunculiasis (guinea worm disease). In countries where water is improperly disinfected, stick to bottled or canned carbonated beverages, beer, and wine. However, be advised that even bottled water in developing countries can be contaminated with bacteria that cause diarrhea, so even bottled water should probably be boiled or disinfected with chemicals or ultraviolet (UV) light before drinking. All containers should be wiped clean to remove external moisture and dirt. All ice should be considered contaminated. For purposes of preserving the environment, it is preferable to carry a reusable water container that is filled with disinfected water than to discard multiple plastic or glass containers.

Do not urinate or defecate (inadvertently) into or near your water supply. Build a latrine 8 to 10 in (20 to 25 cm) deep into the ground at least 100 ft (31 m) and downhill from the water supply. Try to keep the latrine away from a gully or other formation that might become a runoff stream during a thaw or after heavy rainfall.

“Raw” drinking water 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, through a filter or fine cloth. Coagulation and flocculation techniques 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, and then pour off the upper (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. The usual advice—to boil water for 5 to 10 minutes plus 1 minute for each 1,000 ft (305 m) of altitude above sea level—is probably overkill. Giardia cysts are instantly killed in water heated to 158°F (70°C). To play it safe, bacteria and most viruses require a few minutes at this temperature. Hepatitis A virus requires a full minute of boiling to ensure inactivation.

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 5 to 10 minutes of boiling at sea level.

The temperature at which water boils varies with altitude because of the surrounding barometric pressure. Barometric pressure is expressed in terms of the height (in inches or millimeters) of a column of mercury (Hg) that exerts a pressure equal to that of a column of air with the same size base. At sea level (barometric pressure 760 mm Hg), water boils at 212°F (100°C); at 5,000 ft, or 1,525 m (632 mm Hg), 203°F (95°C); at 10,000 ft, or 3,050 m (522 mm Hg), 194°F (90°C); at 14,000 ft, or 4,270 m (446 mm Hg), 187°F (86°C).

Thus, boiling water is effective for disinfection at any altitude below 18,000 ft (5,490 m) likely to be attained by a wilderness enthusiast. The time required to heat the water to boiling contributes to the disinfection process. To provide a wide margin of safety, boil the water for 3 minutes.

Halogens, such as iodine and chlorine, are effective chemical disinfectants. The rate at which they kill microorganisms depends on 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 4 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.

2. Add one tablet of fresh tetraglycine hydroperiodide (Potable Aqua, Globaline, Coughlan’s, EDWGT) to 1 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 1 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. Potable Aqua Plus treatment includes an oxidizing tablet to remove the iodine taste. Granular activated charcoal removes organic material, chemicals, and radioactive particles by adsorption, but does not remove all microorganisms, and thus cannot be relied on 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, to disinfect them.

3. Add 8 to 10 drops (0.5 mL in each drop) of standard 2% 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% 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

4. Fill a 1 oz (30 mL) glass bottle with iodine crystals (U.S. Pharmacopeia [USP] grade, resublimed: 2 to 8 grams), and then fill the bottle with water. The bottle should have a paper-lined Bakelite cap. Warm the water to 68°F to 77°F (20°C to 25°C). Shake vigorously, and 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% 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

5. Filter the water through a category-three (as set for purification by the Environmental Protection Agency) water treatment device. Manufacturers who sell filtration devices are 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 4 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 (see below) 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.

6. Maximum filter pore sizes (in material or microns) for removing microorganisms are as follows: dracunculus (guinea worm) larvae—coffee filter or fine cloth; schistosome cercariae—coffee filter or fine cloth; parasitic eggs and larvae—20; Giardia lamblia cyst, Entamoeba histolytica cyst, Cyclospora—3 to 5; Cryptosporidium oocyst—1; enteric bacteria (such as E. coli) —0.2 to 0.4; and viruses—0.004 to 0.01.

7. Halazone (a mixture of monochloraminobenzoic and dichloraminobenzoic acids) and other chlorine (bleach) products have been considered less effective for field water disinfection. Halazone has been characterized as losing 75% of activity after 2 days’ continuous exposure to air with high heat and humidity; having a shelf life of 6 months; and decreasing potency by 50% after storage above 104°F (40°C). Therefore, you should obtain a new bottle every 3 to 6 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	7 tablets for 15 minutes
	2.5 tablets for 30 minutes	5 tablets for 30 minutes
cold	5 tablets for 60 minutes	7 tablets for 60 minutes