Dedicated to Mara's travel and hiking adventure journals as well as her words of wisdom and suggested resources for hikers and travelers.
This chart of water treatment options is not meant to provide exhaustive information about all options. But, it could be a good place to start your own research.
What's in the water?
Unfortunately, water in the backcountry may be contaminated. Contaminants include viruses, bacteria, giardia, cryptosporidium, and chemicals from industrial and agricultural runoff. Not all treatment options work on all of these and none of the above options remove chemical pollutants. Thankfully, avoiding water downstream from chemical plants and industrial manufacturers is not usually a problem in the backcountry.
It's also best to avoid glacial meltwater if possible. That meltwater, often milky in appearance, is full of silt which not only may clog your filter, but may also clog your internal organs.
Why avoid these pollutants?
These pollutants can cause all sorts of medical problems, mostly likely among them, intestinal bugs. From what I've read, not everyone is predisposed to harbor intestinal bugs. For example, Giardia will only infect about 50% of the people who are exposed to it. Of those, only a small percentage will have symptoms (and nasty symptoms, at that). The rest of those infected will be carriers and unknowingly spread giardia as they go. Keep this in mind when you hear from those who've never had to deal with intestinal problems.
The one time I got giardiasis in the US, it was from a trip on the Long Trail in VT. I accepted water from someone who used a filter. I realized only after drinking the water that he failed to keep his intake and output hoses separate and had likely contaminated his own water.
The best write-up I've read about diarrhea in travelers can be found at the CIWEC Clinic web site (now at the Internet archive). I was actually treated at the clinic (in its 1997 location) by Dr. Shlim long before I found this write-up. I had a referral to him from my doctor even before I left the U.S.
I know the instructions for iodine tablets mention this, and I'm pretty sure the instructions for other chemical treatments do too, but after the chemicals have been added and had time to start working, loosen the cap just a bit and tip the bottle so that the treated water drips through the threads on the bottle. Then, retighten the bottle and let the chemicals finish purifying the water.
I use a film canister over my bite valve to keep it off the ground and other suspect areas.
When cooking dinner, I bring the water to a boil before I add any of the food. This gives me a chance to dunk my spoon and my cup. A brief dunking is enough to kill most contaminants.
This should be enough to kill just about anything you'll encounter along most US hiking trails. When traveling, you may have to boil longer or use another method to deal with Cryptosporidium.
With the weight and bulk of water filters, I've never bought a filter and have only used them infrequently while sharing gear with friends along the trail. I used iodine on my Appalachian Trail thruhike and continued to use iodine for a few years but have now switched to Aqua Mira.
Last updated, January 8, 2016.
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