Outdoorsman: Water Filtration/Purification

October 2, 2002
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You need water, but the water must be clean. Ingesting contaminated water could lead to problems that increase dehydration or even worse. Some waterborne organisms cause gastrointestinal diseases, which can lead to prolonged diarrhea, fever, weakness and dehydration. Then there are organisms that can enter your bloodstream where they will live as parasites and cause disease. So, lets talk about how to clean up your drinking water.


The intent of filtration is to screen out harmful substances. There are highly effective filter systems that are lightweight and easily portable for backpacking and camping. But you have to be careful before buying a water filter. Some units are nothing more than taste improvers that will remove a foul odor or flavor, but not much more. There are two types of filters worth considering: membrane and depth. Membrane-type filters employ porous sheets that allow water to pass through, but block anything larger than the pore size. The good thing about membrane-type filters is that they are easy to clean. The downside is that they can clog up quickly. Depth-type filters employ a dense, yet porous filtering element (such as a ceramic block) to screen out particulates as the water is forced through the material. These filter elements can be cleaned by scrubbing or backwashing. If the system includes a carbon filter component, it is also able to eliminate certain chemicals and heavy metals. These filter elements need to be handled carefully during cleaning to prevent them from cracking. As part of my backcountry equipment, I have used and gained confidence in the MSR MiniWorks filter and the Pur Explorer filter. The MSR unit is an older model thats no longer sold, but the company still offers quality water-filtration products.


The idea behind chemical treatment of drinking water is to poison all the little critters that are swimming in your drink. Iodine and chlorine are the old standbys in the water purification game. The key to safe use of these products for human consumption is to carefully follow manufacturer recommendations. Additional caution must be exercised because some people have chemical sensitivities or are allergic to some of these substances (particularly iodine). The effectiveness of a chemical purifier depends upon product freshness, water temperature, water clarity, exposure time, and dosage. Check the expiration date on the product package to make sure the chemicals are fresh. For more effective purification, raise the water temperature to 60 degrees F or above. Pre-filter or let the water stand overnight to allow impurities to settle, and then treat only the clear water. Allow the recommended treatment time, and use the full dose of chemical. Chlorine is used all across the United States to treat city tap water before its delivered to residential customers. For camping situations, products such as Halizone have been popular through the years. Regardless of what brand you use, always carefully follow the directions. Iodine comes in both tablet and liquid form. Use tablets exactly as directed. The recommended dosage for liquid iodine is five drops of 2 percent tincture of iodine in a quart of clear water. If the water is cloudy or especially cold, increase the dose to 10 drops. Shake the container to disperse the iodine and then let it stand for 30 minutes before drinking.


A water filter is not the same as a water purifier. Filters, as discussed, only screen out particulates down to a certain size, and they may remove some chemicals. But viruses are so small they can slip right through the filter element. Thats when you need a full-blown water purification system. When the water is risky, I use a Sweet-Water Guardian Purifier System, which utilizes a chlorine-based liquid called ViralStop to do the actual purifying. The procedure is to filter the water first, then add five drops of ViralStop per liter of water and wait five minutes before drinking. If you dont have a purifier, but you still want to ensure against viral contamination, there are three methods you can use. First, pre-treat the water with iodine or a chlorine-based purification chemical to kill the organisms, and then run the water through the filter to remove the chemical taste and odor, as well as most of the dead microbes. Second, you may filter the water first, and then treat with the chemical purifiers. Or third, boil the water, which were coming to next.


The thermal approach involves cooking to death the little devils that have contaminated your drinking water. To kill harmful organisms, boil water (a full, rolling boil) for one minute at sea level, and add one minute for each additional 1000 feet above sea level. If youre unsure of your elevation, boil the water for 10 full minutes just to be on the safe side. Boiling can leave water tasting flat, but that can be somewhat overcome by shaking or stirring some air back into the water.


Boiling or chemically treating water can often leave it with a foul taste or smell. These undesirable characteristics can sometimes be removed by running the water through a quality filter after treatment. Or you can stir a pinch of charcoal from your campfire into the water and then let it stand for 45 minutes. You might also try adding a pinch of salt per quart or flavoring the water with something like lemonade mix. Stirring about 50 mg of a crushed vitamin C tablet into treated water can also help eliminate the taste and color of the iodine. All of this may sound like a pain in the neck just to get a good drink of water. But if youve ever experienced an intestinal tract ailment caused by ingesting something nasty with your water, youll opt for a little pain in the neck rather than a pain in the gut anytime.

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