Safe water is essential for adequate hydration. Destruction and removal of harmful organisms through disinfection produces safe drinking water. Bacteria, viruses, and protozoa are the most common causes of water contamination for climbers. The risk of illness from contaminated water depends on the concentration of organisms, volume of water consumed, and the treatment method used. Killing all life forms, called sterilization, is not necessary for safe drinking water. Instead, the desired outcome of water disinfection is to reduce the number of infectious organisms to an acceptably low number, thus eliminating the possibility of gastrointestinal illness. Figure E-1 illustrates the four major waterborne pathogen types, with examples of each within the corresponding column.
Cloudy water indicates a higher risk of contamination, yet even clear water should be assumed to be contaminated. Appearance, odor, color, and taste are not reliable indicators of tainted water. Water sources that are near human or animal activity are commonly contaminated with fecal pollution containing enteric pathogens that trigger gastrointestinal illnesses.
Water should always be pretreated to remove large and small debris, which can interfere with the disinfection process. This can be accomplished by allowing the water to stand (sedimentation), by screening for larger particles, or by using the coagulation-flocculation method for smaller particles or cloudy water. Sedimentation occurs by leaving water unmoved for a number of hours and allowing gravity to pull large particles to the bottom of a container. The surface water can then be decanted or filtered from the top. Screening removes the largest particles from water and can be accomplished by pouring water through clothing or a coffee filter. Coagulation-flocculation is necessary for particles that are not large enough for gravity or filtration to be effective. This is accomplished by adding a nontoxic powder such as alum, iron, lime, white ash from burned wood, or baking powder to the water. These substances cause particles in the water to agglomerate into small particulates. Following coagulation, larger particulates are formed through gentle agitation in the flocculation step. After a 30-minute settling period, these larger clusters are removed through screening, sedimentation, and/or decanting. Charcoal may also be incorporated to remove any chemical contaminants in water, though this can be difficult in a wilderness setting. The easiest pretreatment method for climbers is usually the screening method, though the other methods are useful in a base camp situation. Figure E-2 outlines advantages and disadvantages of different techniques.
Bacteria |
Viruses |
Protozoa |
Parasites |
Escherichia coli |
Hepatitis A, E |
Giardia lamblia |
Ascaris lumbricoides |
Shigella |
Norovirus |
Entamoeba histolytica |
Hookworm |
Campylobacter |
Poliovirus |
Cryptosporidia |
Tapeworm |
Vibrio cholerae |
Rotavorus |
Blastocystis hominis |
Sheep liver fluke |
Salmonellae |
|
Isospora belli |
Dracunculus medinensis |
Yersinia enterocolitica |
|
Balantidium coli |
Pinworm |
Aeromonas |
|
Ancanthamoeba |
Whipworm |
|
|
Cyclospora |
Oriental liver fluke |
|
|
|
Lung fluke |
|
|
|
Fish tapeworm |
|
|
|
Hydatid disease |
Source: Backer HD. Field Water Disinfection. In: Auerbach PS, ed. Wilderness Medicine. 7th ed. Philadelphia, PA: Mosby Elsevier; 2017. |
|||
FIGURE E-2. ADVANTAGES/DISADVANTAGES OF DIFFERENT TREATMENT TECHNIQUES
Pre-treatment technique |
Process |
Advantage/Disadvantage |
Sedimentation |
Large particles settle by gravity |
Improves water aesthetics Takes a long time |
Screening |
Large particles are removed |
Removes large particles Easy Improves water quality, efficacy of filtration, and chemical disinfection |
Coagulation-flocculation |
Suspended particles are removed |
Removes smaller particles Easy Improves water quality, efficacy of filtration, and chemical disinfection |
Activated charcoal |
Removes chemicals |
Removes pesticides and chemical disinfectants Improves taste |
Climbing destination is an important factor in determining potential contaminants and identifying the best methods for safe water collection. Methods of treatment include heat, filtration, chemical treatment, and irradiation. These methods, along with the common contaminants that are neutralized using each, are illustrated in Figure E-3.
Heat is the surest method to kill all enteric pathogens. Many organisms are killed at temperatures lower than the boiling point of 100°C (212°F). Lower temperatures can be effective if the contact time is longer (pasteurization), but without a thermometer it is too difficult to accurately gauge the temperature. Boiling is the most certain method to eradicate all pathogens, ensuring the appropriate temperature has been reached. According to the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC), bringing water to a boil at sea level is sufficient, and the Environmental Protection Agency (EPA) suggests an extra one to three minutes for an added margin of safety (Backer 2012). For alpine climbers, altitude must be considered, as it decreases the boiling point. Figure E-4 indicates the boiling temperatures at various altitudes.
Disinfection techniques |
Heat |
Filtration |
Halogens |
Chlorine dioxide |
Bacteria |
good |
good |
good |
good |
Viruses |
good |
fair |
good |
good |
Protozoa-Giardia |
good |
good |
good |
good |
Protozoa-Cryptosporidium |
good |
good |
poor |
good |
Parasites |
good |
good |
fair |
fair |
Sources: Backer HD. Field Water Disinfection. In: Auerbach PS, ed. Wilderness Medicine. 7th ed. Philadelphia, PA: Mosby Elsevier; 2017. |
||||
The CDC recommends boiling water for three minutes when higher than 2,000 meters (Backer 2012). Prior to boiling water, the removal of debris (pretreatment) should be completed, but is not completely necessary, as heat kills all enteric pathogens regardless, and there are no alterations in the taste. The limitation of using heat is the fuel source and amount required. It generally takes one kilogram (2.2 lb.) of wood to boil 1 liter of water. Be aware of local and national rules and regulations regarding the use of wood, and be environmentally friendly.
FIGURE E-4. BOILING TEMPERATURE AT VARIOUS ALTITUDES
Altitude (M) |
Altitude (ft) |
Boiling point °Celsius |
Boiling point °Fahrenheit |
|
1,500 |
4,921 |
95° |
203° |
|
3,050 |
10,006 |
90° |
194° |
|
4,250 |
13,944 |
86° |
186.8° |
|
5,800 |
19,028 |
81° |
177.8° |
|
Sources: Backer HD. Field Water Disinfection. In: Auerbach PS, ed. Wilderness Medicine. 7th ed. Philadelphia, PA: Mosby Elsevier; 2017. |
||||
Filters remove cysts and bacteria, but are not reliable for complete removal of viruses. Viruses can be as small as 0.1 micron in diameter, and filters are unable to reliably remove items that small. Filters are simple, do not alter the taste, and require no curing time. The downfalls of filters are cost, weight, size, and reliability, as they can malfunction due to clogging. All models require pressure to drive the water through the filter, and the smaller the pore size the more pressure is required. Filters require additional pressure once congested with contaminants, which can force organisms through the filter, yielding contaminated water. All filters require cleaning, and the ability to easily service the unit in the field is a plus. Back flushing and surface cleaning usually clears the filter.
Filters can be divided into microfilters, ultrafilters, and nanofilters, which have pores as small as 0.1, 0.01, and 0.001 or less microns, respectively. This attribute defines their abilities. Ultrafiltration is considered sufficient to remove viruses from water while nanofiltration can filter even smaller particles (e.g., chemicals). The surest method for safe drinking water that may have viral contaminants is a combined treatment of filtering and one other method (heat, halogens, chlorine dioxide, or ultraviolet light) to eradicate viruses. Filters can be utilized without the addition of another disinfection method in areas where human or animal contact is limited.
Some filters come with integrated charcoal or iodine elements. Charcoal is the optimal technique to remove toxic chemicals and radioactive contaminants, with the added bonus of improved taste and odor. Unpleasant taste and odor can be the initial sign of ineffective charcoal. Iodine is impregnated into some filters in an attempt to destroy viruses as water passes through the filter.
Reverse osmosis filtering units are available but unrealistic for climbers, as this type of filter is used for desalinating water and is more applicable for recreation near the ocean or saltwater lakes.
Halogens eliminate bacteria, but their effectiveness against protozoa is not guaranteed. Halogens include iodine and chlorine, and their effectiveness depends on the concentration, time, water temperature, contaminants, and pH of the water. In cold water, the contact time or overall dose should be increased. For areas where giardia is common, the contact time must be at least three to four times longer in cold water. The optimal pH for halogen disinfection is 6.5 to 7.5, and when the pH is more alkaline and closer to 8.0, a larger dose of halogen is required. Certain desert water is very alkaline and not palatable. Equipment to test water pH is not a common tool taken by most climbers, and compensating for the pH is not necessary as most halogens have some buffering capacity for minor pH differences.
Most climbers find that halogens have an unpleasant taste that requires a second step to neutralize. For treatment times and information, the product label should always be referred to prior to use.
Iodine is effective for killing bacteria, viruses, and some protozoa. Iodine use should be limited to one month and should not be used by pregnant women, iodine-sensitive individuals, or climbers with thyroid disease, a family history of thyroid disease, or who suffers from chronic iodine deficiency (Figure E-5).
After adequate disinfection, flavoring can be added to improve the taste, such as ascorbic acid (vitamin C) in drink mixes or sodium thiosulfate.
Chlorine, such as household bleach (5% sodium hypochlorite), is sufficient to inactivate bacteria, viruses, and some protozoa (Figure E–5). It is more sensitive and less suitable in cold contaminated water. Acute toxicity or irritation is extremely rare and only occurs if solutions are highly concentrated. It does become less potent when exposed to heat, air, or moisture, and to extend the shelf life, the manufacturer packages chlorine tabs individually in foil.
FIGURE E-5. USE OF IODINE AND CHLORINE FOR WATER PURIFICATION
Iodine techniques |
Clear surface |
Cloudy water |
Iodine tabs |
1 tab |
2 tab |
2% iodine solution |
1 mL |
2 mL |
10% Povidone-iodine |
4 mL |
8 mL |
Iodine crystals in water (4-8g of iodine in 1-2oz bottle filled with water) |
13 mL |
26 mL |
Iodine crystals in alcohol (8g iodine to 100ml of 95% ethanol) |
1 mL |
1 mL |
Chlorination techniques |
|
|
Household bleach 5% |
1-2 mL |
2-4 mL |
Calcium hypochlorite |
1/4 tab |
1/8 tab |
Sodium |
½ tab |
1 tab |
Chlorine plus flocculating agent |
½ tab |
1 tab |
To reduce the taste and smell of chlorine, several drops of 30% hydrogen peroxide solution can be added, forming calcium chloride, a common food additive. Again, this requires a second step, as the peroxide should not be added until at least ten to fifteen minutes after the chlorine tab. Flavored drink mixes containing ascorbic acid can also mask the unpalatable halogen taste of chlorine.
Halogens can be used independently unless water sources are contaminated with protozoa. Giardia requires longer contact time with higher concentrations and cryptosporidium cysts are resistant to certain halogens. Halogens can be combined with chlorine dioxide or ultraviolet light to eradicate the protozoa.
This agent is effective against all microorganisms, including cryptosporidium. It has no taste and is very portable in small doses. Chlorine dioxide is sensitive to sunlight and should be kept in a shaded bottle during treatment. Aquatabs® are a common brand of chlorine dioxide. This is the single most effective and weight-conscious solution for water disinfection, and a good choice for most climbers and alpinists.
The Miox purifier uses a current passed through a brine solution that generates free chlorine as well as other mixed disinfectants. This creates an environment that is effective against bacteria, viruses, and sometimes cryptosporidium. The battery life for this device creates an element of uncertainty for this method. Climbers in the alpine setting should keep a spare set of batteries close to their body not only for a backup but also to prolong the battery life when not in use. These purifiers can be difficult to use. They are listed here to be comprehensive, but in the opinion of the authors would not be a preferred water treatment tool.
This method is used in Europe. The EPA in the United States has not approved it for use and therefore it is limited to purchase and use at overseas climbing destinations. Silver can be used to treat water contaminated with bacteria and for the prevention of growth in previously treated or stored water. Some filters are silver-impregnated to inactivate bacteria during filtration, and this element decreases the growth of bacteria on the inside of the filter. Silver will need to be combined with another method if there is a chance of the presence of viruses or protozoa in the water being treated. Note that long-term ingestion of large volumes of silver has been implicated in the development of argyria, a condition causing blue skin (James 2006).
Ultraviolet light is an effective method to kill bacteria, viruses, and protozoa. This method works rapidly and does not alter the taste. It is important for the user to remember that there is no residual effect and water may become recontaminated. In other words, if you add additional water to the container, you must activate the ultraviolet light again to disinfect. While some units have solar panels integrated into the unit, most require batteries, which are sensitive to temperature and can become ineffective when climbing in cold environments. As with the Miox purifier, extra batteries are essential, and keeping them warm in cold climates is helpful. These are effective against cryptosporidium. This method can be used as a single method against all contaminants. The most common example of this water disinfectant method is the SteriPEN.
Solar irradiation (sunlight) is used with a SolarBag and can disinfect up to three liters of water. The bag has a mesh insert coated with titanium dioxide. The unit is placed in direct sunlight for one to two hours or two to four hours on a cloudy day. A dye can be used to indicate when the water is safe to consume. This method should be combined with other methods if viruses and protozoa are a possibility.
Another form of solar irradiation can be conducted using clear water bottles, preferably made of polyethylene terephthalate (PET), which have the least amount of additives. Irradiation occurs if the bottle is placed upon a reflective metal surface in the sun for up to four hours, or if the water is cold, for up to six hours. Glass should not be used, as it inhibits the UV from penetrating the contained water with as much effectiveness as clear plastic. For cloudy water, the time of exposure to UV rays should be extended for at least two days. While this can be a low-cost treatment method against bacteria, viruses, and protozoa, the large amount of time needed for disinfection makes this method unsuitable for climbers. This method should be combined with another to ensure cleanliness.
FIGURE E-6. CHOOSING THE APPROPRIATE DISINFECTION TECHNIQUE IN THE VARIOUS ENVIRONMENTS
Effective methods for various concerns |
Wilderness water with little human or domestic animal activity |
Tap water in 2nd or 3rd world country |
Clear water near human and animal activity |
Cloudy water near human and animal activity |
Primary concern |
bacteria, giardia |
bacteria, giardia, viruses |
All pathogens |
All pathogens |
Disinfection method |
Any method |
Heat, or filtration plus halogen, chlorine dioxide, or ultraviolet method |
Heat, or filtration plus halogen, chlorine dioxide, or ultraviolet method |
Pretreat with coagulation, flocculation plus heat, or filtration plus halogen, chlorine dioxide, or ultraviolet method |
Sources: Backer HD. Field Water Disinfection. In: Auerbach PS, ed. Wilderness Medicine. 7th ed. Philadelphia, PA: Mosby Elsevier; 2017. |
||||
There are multiple options for water treatment and the best method should take into account likely infective organisms, personal taste, group size, location, and available fuel. As a general guideline, pristine watershed areas can be considered free of viral agents; however, it can be very difficult to determine who or what has been in the area. With increasing human and animal contact, viral contamination becomes more of a risk. The prudent action would be to adhere to the principle that all wilderness water sources are contaminated and treat accordingly. Boiling will eliminate all pathogens but may not be feasible. Overseas, the use of Aquatabs®, which are effective against all contaminants, even cryptosporidium, is recommended. There is a time delay with this method, and the manufacturer’s recommendation must be precisely followed. SteriPENs are a great method for all contaminates as long as the water is not extremely cloudy or full of large particles. Batteries can be a challenge, and in certain climbing destinations other methods may be more advantageous. Water treatment, strict personal hygiene, and proper waste management methods are the best practices to remain free of illness. Figure E-6 summarizes safe water disinfection strategies.