It was a few years ago now, but I remember it like yesterday. You don't forget something like that. It's too uncomfortable to forget. I was on Mount Baker and I drank some bad water. You can imagine what happened next. It wasn't pretty.
There are two major water-born protozoa that climbers must be aware of. Both Giardia and Cryptosporidium occur in lakes, rivers and streams throughout North America. They each take two to twenty days to manifest themselves. The most common symptoms of these protozoa are nausea, diarrhea, fever, headaches, stomach cramps, flatulence and belches that reek like rotten eggs.
In addition to protozoa, climbers must be concerned about viruses and bacteria in the water. We don't have to worry about water-born viruses too much in North America. Infectious hepatitis and other viruses are more commonly found in tropical waters. Bacteria such as salmonella and Escherichia coli may be found in some contaminated mountain water sources and alpinists should protect themselves against them.
There are three common ways to treat problematic water. The first way is to boil it, the second way is to disinfect with chemicals and the third way is to filter it.
There is perhaps no better way to kill anything that might live in the water and wants to live in your stomach than to boil it. Some people argue that you must bring your water to a boil for ten minutes. The reality is that if you bring the water to a rolling boil and then turn off your stove, anything that might be a real problem will be taken care of.
It's common for guides to use iodine to treat their water. Iodine tablets effectively kill viruses and bacteria...and they also effectively make the water taste terrible. Iodine is less effective agains Giardia and Cryptosporidium.
There is the possibility that too much iodine may be bad for your thyroid. This may not be too big of a deal for weekend warriors, but for those who spend a significant amount of time in the field, this could pose a serious health risk.
Another chemical, chlorine dioxide, is gaining popularity for treating water. This chemical reliably kills viruses, bacteria, Giardia and Cryptospridium, however the contact time required for killing protozoa may be unacceptably long for some climbers.
These are heavy items for alpinists to carry, but they do provide the quickest filtration. And though water filters do an excellent job removing protozoa, most models are less effective in with viruses and bacteria. A small percentage of the filters on the market include an integral iodine chamber that will treat the water for additional pathogens, but these models are more expensive, less common and may not always be effective.
There was a time when it was possible to trust running water in the mountains. That time is long gone. Today the wisest course of action is to treat all of the water that you drink...that or risk the uncomfortable consequences.
--Jason D. Martin