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. While my method works has worked for me, you shouldn’t adopt it without considering your own geographic and topographic situation and the types of trips you are planning.
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.
By examining topographic maps, before heading on trips I’m aware generally aware of current and historical mining activity and the locations of towns, sewage treatment facilities, septic fields and backcountry huts and campgrounds. This knowledge helps me to avoid drinking water downstream from these possible sources of contamination.
I also obtain current local information when possible. In the backcountry, I keep on the look out for animal and human faeces, the frequency of other travellers on the trail, especially those with dogs and the proximity of backcountry campgrounds and toilet facilities to water sources. Above all, I strive to take my drinking water from as high up in the alpine as possible and always from above areas of human activity.
For treatment, I generally rely on a MSR Waterworks II microfilter 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. 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.