I've been meaning to post this for a while... its about 4 pages long if printed out, so feel free to skip it. But its got some real good information. Enjoy.
Water Purification vs. Filtration
First, lets detail in layman's terms, the difference between purification and filtration, and then examine when either or both might be appropriate or perhaps even necessary.
Biologically contaminated water, is water that contains microorganisms, such as viruses, bacteria, cryptosporidium, etc. These microorganisms will lead to intestinal disorders and infections (and untreated, even death). This water requires purification. Purification kills all the bad stuff living in your water, and is usually accomplished via a chemical process. The following products are common examples of chemicals, which when used properly, will purify your water; sodium hypochlorite, iodine, purification tablets, chlorine dioxide, etc. Heat and UV light can also be used to purify water. Keep in mind that purification will not actually remove anything from your water, like pesticides, unwanted chemicals, heavy metals, etc. It only kills living organisms. It is important to note, that one must be mindful in choosing a purification method, as a variety of extenuating circumstances will determine the effectiveness of each purification method used, when pitted against different organisms and under different conditions.
Toxic water contains chemical contamination from pesticides, mine tailings, and so on. For the sake of this discussion, we will also include dirty, murky or otherwise unusable water, in the toxic water category. This water must be filtered to be safe to drink. Filtration removes these unwanted ingredients from your water, so long as what you're filtering out, is larger than the pores of your filter. Think of a coffee filter, and how it keeps the coffee grounds out of coffee. The same principal applies here, only to do the job you need done, a much finer filter is required... so think in terms of microns. To put this into perspective, 600 microns will fit in the period at the end of this sentence. Most things from both biologically contaminated and toxic water, can be removed via filtration... but not everything. Thus the need for purification. Just as purification will kill microorganisms, but will not remove toxins, and thus the need for filtration.
Dipping your head into a cold mountain stream and taking a long refreshing drink, is an experience that has basically vanished from the wilderness areas of America. With the increased use of the wilderness, there has also been an increase in the amount of bacteriological and chemical contamination, of backcountry water supplies. The U.S. Environmental Protection Agency reports that 90 percent of the world's water is contaminated in some way. There are a variety of microscopic organisms that can contaminate water supplies and cause potentially serious, even fatal illnesses, among wilderness travelers. The primary danger in the backcountry from these infections, is fluid loss due to diarrhea and vomiting, which can lead to hypovolemic shock and possibly death (study up on fluid electrolyte replacement, and shock, to learn more about treating shock). But our goal here, is to avoid this all together.
In order to drink the water you find, you should be prepared to treat it. There are numerous methods for water purification, described below in order of effectiveness. Remember however, that infections can also be spread through poor personal hygiene, something that purifying your water won't prevent. So wash your hands... often.
Boiling is the most certain way of killing all microorganisms. According to the Wilderness Medical Society, water temperatures above 160°F (70°C) kills all pathogens within 30 minutes and above 185°F (85°C) within a few minutes. So in the time it takes for the water to reach the boiling point of 212°F (100°C) from 160° F (70°C), all pathogens will be killed, even at higher altitudes. To be extra safe, let the water boil rapidly for one minute (especially at higher altitudes, since water boils at a lower temperature there).
There are two common types of chemical treatment; those using iodine, and those using chlorine (for another option, see the MIOX, by MSR). There are a variety of products on the market, so follow the directions on the container. Be advised that many of the tablets have an expiration date and become ineffective after that point. Also, once the container has been opened, the tablets must be used within a certain period of time. When in doubt, buy a new container. Remember that chemical purification methods may only be partially effective, depending on the temperature of the water you are treating.
General Chemical Treatment Procedures
• The effectiveness of all chemical treatment of water is related to the temperature, pH level, and clarity of the water. Cloudy water often requires higher concentrations of chemical to disinfect.
• If the water is cloudy or filled with large particles, strain it, using a cloth, before treatment. Large particles, may have been purified only, "on the outside."
• Add the chemical to the water and swish it around to aid in dissolving. Splash some of the water (with the chemical already in it) onto the lid and the threads of the water bottle, so that all areas are treated.
• The water should sit for at least 30 minutes after adding the chemical, to allow purification to occur. If using tablets, let the water sit for 30 minutes after the tablet (or tablets) have dissolved.
• The colder the water, the less effective the chemical is as a purifying agent. Research has shown that at 50°F (10°C), only 90 percent of Giardia cysts were inactivated after 30 minutes of exposure. If the water temperature is below 40°F (4°C), double the treatment time before drinking. It is best if water is at least 60°F (16°C) before treating. Consider placing the water in the sun to warm it up before treatment.
• Chemically treated water can be made to taste better by pouring it back and forth between containers, after it has been adequately treated. Other methods include adding a pinch of salt per quart or adding flavorings (lemonade mix, Kool-Aid, etc.), once again, after the chemical treatment is completed.
Iodine is light sensitive and must always be stored in a dark bottle. It works best if the water is over 68°F (21°C). Iodine has been shown to be more effect than chlorine-based treatments in inactivating Giardia cysts. Be aware that some people are allergic to iodine and cannot use it as a form of water purification. Persons with thyroid problems, who are on lithum, women over fifty, and pregnant women, should consult their physician prior to using iodine for purification. Also, some people who are allergic to shellfish are also allergic to iodine. If someone cannot use iodine, use either a chlorine-based product, or a non-iodine based filter, such as the PUR Hiker Microfilter, MSR WaterWorks, or the Katadyn Water Filter. Generally, the procedure for iodine is as follows:
• Liquid 2% Tincture of Iodine Add 5 drops per quart when the water is clear. Add 10 drops per quart when the water is cloudy.
• Polar Pure Iodine Crystals Fill the Polar Pure bottle with water and shake. The solution will be ready for use in one hour. Add the number of capfuls (per quart of water treated) listed on the bottle, based on the temperature of the iodine solution. The particle trap prevents crystals from getting into the water being treated. It is important to note that you are using the iodine solution to treat the water, not the iodine crystals. The concentration of iodine in a crystal is poisonous and can burn skin tissue and eyes. Let the treated water stand for 30 minutes before drinking. In order to destroy Giardia cysts, the drinking water must be at least 68°F (20°C). The water can be warmed in the sun before treating or hot water can be added. Refill the treatment bottle after use, so that more solution will be ready one hour later. Crystals in the bottle make enough solution to treat about 2,000 quarts. Discard the bottle when it's empty.
• Potable Aqua This is an iodine tablet product. Follow the manufacturer's instructions for use.
Chlorine can be used for persons with iodine allergies or similar restrictions. Remember that water temperature, sediment level, and contact time, are all elements in killing microorganisms in water. Halazone is an example of a chlorine tablet product. To use, follow the manufacturer's instructions.
Tricks of the Trail
Always have at least one backup method for water purification in case one fails. This can be any combination of methods. Be the cautious person, and always have two backup methods: water filter and 2% tincture of iodine, or Polar Pure iodine crystals. You can always boil the water. If boiling is your backup method, make sure you have enough fuel.
Adding vitamin C (about 50 milligrams) to iodized water, completely eliminates any taste or color of iodine. You must wait until the iodine has purified the water before adding the vitamin C. The vitamin C in drink mixes like Tang™ has the same effect.
There are a number of devices on the market that filter out microorganisms and toxins. A water filter pumps water through a microscopic filter that is rated for certain-sized organisms and particles. The standard size rating is in microns. Depending on the micron rating of the filter, smaller organisms (like viruses) can pass through. Be cautious when selecting a filter. You should know what potential organisms you need to treat for, by studying the area you will be in. You don't want to go to an area where a virus like Hepatitis A is present in the water (a problem in many developing countries) with a filter that will handle only a larger organism like Giardia.
Common microorganisms and the filter size needed
Organism Examples General Size Filter Type Particle Size Rating
Protozoa Giardia, Cryptosporidium 5 microns or larger Water filter 1.0-4.0 microns
Bacteria Cholera, E. Coli, Salmonella 0.2-0.5 microns Microfilter 0.2-1.0 microns
Viruses Hepatitis A, Rotavirus, Norwalk virus 0.004 microns Water purifier to 0.004 microns
Two basic types of filters
• Membrane Filters, which use thin sheets with precisely sized pores that prevent objects larger than the pore size from passing through. Pro: Relatively easy to clean. Con: Clog more quickly than depth filters. Example: PUR-Hiker.
• Depth Filters, which use thick porous materials such as carbon or ceramic to trap particles as water flows through the material. Pro: Can be partially cleaned by backwashing. Activated carbon filters also remove a range of organic chemicals and heavy metals. Con: Rough treatment can crack the filter, rendering it useless. Examples: MSR WaterWorks II, Katadyn.
Note: Remember, there is a difference between a water filter and a water purifier. Filters do not filter out viruses, but there are some water purifiers, like the PUR Scout, that pass the water through both a filter and an iodine compound, that kills any smaller organisms that have passed through the filter. These purifiers kill all microorganisms down to 0.004 microns; however, this filter should not be used by people who are allergic to iodine.
Common Practices for Using a Water Filter
• Filter the cleanest water you can find. Dirty water or water with large suspended particles will clog your filter more quickly.
• Prefilter the water through either a prefilter on the pump, or strain it (through a bandanna, coffee filter, etc).
• If you must filter dirty water, let it stand overnight for the particles to settle out.
Tricks of the Trail
Some water filters come as sealed cartridges, making it impossible to inspect the actual filter cartridge. If the filter takes a serious fall, it could crack internally. If the filter inside cracks, unfiltered water can flow through the crack. Treat your filter with care, and if it takes a significant impact, throw it away. Also, remember the intake hose from a water filter, has been submerged in unfiltered water. Treat this hose as "contaminated" and store it in a separate plastic bag.