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I run www.backcountrywater.com which provides comprehensive information on waterborne pathogens, contaminants and treatment systems.
I'm curious about what water treatment method / system different people use in different situations and why. Please post yours below.
Here's my system:
After more than 15 years and across a dozen countries, the treatment system I use has continued to keep me and my companions free from waterborne sickness.
My trips have largely been in mountain areas of North America, Western Europe, the Atlas Mountains of Morocco and New Zealand. Many of these areas have high quality alpine water sources though there is often a significant human and animal presence.
The greatest risks are from Giardia, Cryptosporidium and to a lesser extent bacteria and viruses. There is a small risk of helminth eggs or larvae because of the sheer number of tourists in some areas. There is also the possibility of chemical contamination from ranching, forestry and mining activities.
For treatment, I generally rely on a MSR WaterWorks II microfilter [I sometimes use a MiniWorks EX or a Katadyn Pocket Filter] with a ceramic element that has an absolute 0.5 micron pore size, a built-in GAC element and a secondary paper filter with an absolute pore size of 0.2 microns. In theory, this device should remove all microorganisms down to 0.2–0.3 microns including bacteria, protozoa, and any helminth eggs or larvae. The GAC element removes any offensive taste from the water although mountain water is usually clear and tasteless.
Since pathogenic viruses are generally only present in areas with people, I usually take the risk that the water is virus free or that viruses are clumped together with particles that can be filtered. On occassion I feel that specific water is risky because of a campground or climbers’ hut upstream, the prevalence of human occupation or because I'm drawing water from a river or lake draining a large area. In such cases I first filter the water to remove visible organic matter and silt if necessary. I then treat the water with Polar Pure iodine and let it sit for 20-30 minutes to kill bacteria and inactivate viruses before pumping it through the filter again so the GAC element can remove the iodine.
I've used this method effectively in many places including areas with huge herds of livestock [the Lake District in England] and lots of human faeces [Atlas Mountains]. This combination of microfiltration and halogen treatment is so effective that I'd recommend it for all but the most arduous conditions. The exception is areas with high levels of chemical or heavy metal contamination where no portable treatment system will be 100% effective. On my adventures, I rarely filter water used for soup, tea or coffee because boiling the water instantly kills all pathogens.