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In her monthly column, The Survivalist, Jessie Krebs writes about staying alive in dangerous backcountry scenarios. Krebs is a former Air Force S.E.R.E (survival, evasion, resistance, and escape) instructor and owner of O.W.L.S. Skills.
Finding water in various environments is a crucial survival skill (you can read more about it here). Once you have that skill dialed, it’s important to understand how to take that wild and sometimes unsafe water and make it drinkable. Many use the term “purify” when referring to this, but that term can be misleading. We are not usually eliminating everything except the H2O molecule when treating drinking water. The goal is to remove, bond, or kill things in the water that can potentially harm us. Treated water is not typically “pure” at all, but it is hopefully disinfected.
Boiling used to be the gold standard when it came to disinfection. That was in the days when there weren’t as many toxins and heavy metals in our water, or we were less aware of and concerned about them. Boiling kills living organisms like bacteria, protozoa, cysts, and viruses. When we drink boiled water, we suck down the dead bodies of these little critters along with our water since they can no longer do us any harm. Boiling still does this, of course, but now we have all kinds of non-living and potentially damaging things in water that boiling just concentrates, like pesticides, herbicides, heavy metals, microplastics, leachate, mining waste, superfund site waste, and so on. So it’s a good idea to go beyond boiling, at least in areas where there is a strong possibility of these non-living health threats.
UV exposure is another way to eliminate living organisms from water. Like boiling, though, it cannot rid water of toxins and heavy metals. Additionally, UV treatments are only effective with water that is pretty clear. I’ve been in many situations where my drinking water looked like chocolate milk; a UV pen would not have been effective. They also require batteries, which come with their own issues including weight and proper disposal. That said, exposing contaminated water to direct sunlight for at least 6 hours has helped reduce water borne illness in many lesser-developed countries.
Chemical disinfection is also used in our modern day water treatment plants, and by many outdoor recreationalists. Most of the chemicals used are a type of halogen, usually chlorine or iodine. Adding chemicals to water does not remove the heavy metals or toxins. Chemicals kill or disable organic threats, and may bond to or react with various inorganic compounds, rendering them inert or no longer absorbable by the body. Personally, I prefer to use iodine for water disinfection, since iodine is a necessary nutrient. The military has been using iodine to treat water around the world for decades. Chlorine is commonly used, especially in public water systems, but I prefer not to ingest it, and generally filter it out of tap water when possible.
Filters have gotten really good, and they sure make a difference when it comes to removing bacteria and improving taste. There are a rather dizzying array of filters on the market: hand pump, gravity fed, suction, etc. There are pros and cons to each style of filter. Here’s what I think about when looking for the right filter:
Environmental Impact
I was backpacking in Egypt in 1996, and while visiting Hurghada on the Red Sea, I walked past what used to be the town square, where the locals could come together to trade, celebrate, sell wares, and so on. That day, you could wade almost knee deep in discarded 1.5 liter water bottles. Since then, some filter companies have launched campaigns to donate filters to undeveloped communities. This is great, but I wonder what happens to those products when they reach the end of their lifespan, especially in places where sanitation and disposal is limited. Straw-style personal filters like the ones many backpackers own can filter up to 4,000 liters before they’re bound for a landfill. I now picture that square covered in used water filters.
With that in mind, I consider the environmental impact of a filter when purchasing a new one. What’s it made of? How much energy is used to manufacture it? Is it packaged in a way that prevents needless trash? What will happen at the end of its use cycle? Can it be recycled? Cleaned and reused?
Temperature Range
Below freezing temps can cause micro cracks in a filter, rendering them useless or unreliable. If you like cold-weather wilderness trips, make sure you know how a particular filter performs in that environment, and how to protect your filter from the elements. Some filters perform better than others in the cold; MSR claims that its Guardian Purifier is the only hollow fiber purifier on the market that won’t be damaged if frozen.
Microns Matter
A water molecule is pretty darn small (0.000275 micron), and most bacteria that can hurt us are quite a bit bigger. That said, it can be helpful find out what’s in the water where you’ll be traveling and make sure your filter will remove it. Viruses are generally the smallest contaminant in fresh water to worry about, most falling between .01 and .3 microns in size. Most backpacking microfilters don’t filter out things that small.
Luckily, remote places in North America are rarely contaminated by human-borne viruses, but the more populated an area, the higher the chances are. Beware when traveling to areas with high populations and/or poor sanitation practices. If you suspect viruses may be in the water, look for a purification system that rids water of viruses in addition to bacteria, or consider using some form of chemical treatment. You can also boil your water after filtering it to zap viruses.
Filter Lifespan and Upkeep
The more sediment in the water, the faster a filter becomes clogged. You can remove much of it by pre-filtering with a bandana. But if you think you’ll be in areas with very muddy water, a simple way to clean the filter is a great feature, versus having to change a cartridge and carry the old useless ones home with you. Learn how to fix or clean your filter if it stops working before taking it into the field. Can you do that without tools in the backcountry?