8:01 p.m. on August 20, 2012 (EDT)
Hafford said:
I use a sweetwater filter, and a steripen, the steripen only seems to work about half the time ...
You do not say which SteriPen™ you have. People sometimes have problems with the older models which have the electric contact buttons that must be immersed in the water during the whole treatment duration. If you lift the contacts out of the water during the stirring motion, the UV light will shut off.
I have both an electric contact and an optical sensor model of SteriPen™. I have had no problems with either, nor with the AllClear™ I reviewed for Trailspace a couple months back. I recently ran across another UV treatment device on another website, which I will try to get a link to. Basically, used properly, all the UV treatment devices are 99.9% effective against all the critters that cause problems in the backcountry. Solar UV treatment requires a longer time (6-12 hours of exposure to direct sunlight and a UV-transparent container). They do not remove silt and other things causing turbidity, nor do they remove mining, industrial, or agricultural runoff. Filters do reduce turbidity, but also do not remove the chemicals in mining, industrial, or agricultural runoff.
Contrary to the commonly cited "boil for 5 (or 10 or longer) minutes", it is sufficient to pasteurize water at 155F or hotter for a few minutes to kill all the bacteria, protozoa (and their cysts), and viruses. I refer you to the extensive discussion is Paul Auerbach's 11-pound tome "Wilderness Medicine" for a detailed discussion of this and other water treatment methods (you can also get this in electronic form for your iPad and other electronic "pads" and "tablets"). This means that you can effectively make the water potable (safe to drink, not necessarily surgically sterile) at any altitude you can get to by walking or climbing.
When using chemical treatments (halogens including iodine and chlorine in bleach or chlorine dioxide form), keep in mind that all these halogens take time to act (anywhere from a half hour to days if the water is cold - action time is highly temperature dependent). Chemical treatments, as with filters, UV, and heating are ineffective against chemical contaminants like mining, industrial, and agricultural runoff. In fact, chlorine compounds and chlorine gas combine with a number of agricultural chemicals to produce carcinogens (often cited as the reason that cities along the lower Mississippi have a significantly higher rate of certain cancers than the US as a whole).
Filters must be of sufficiently pore size to remove the critters - 1 micron removes protozoa and their cysts, 0.2 microns removes bacteria and most viruses as well. Be aware of your filter's specifications.
While Ed WhoMe and Big Red are correct that (1) personal hygiene has been shown to be the major cause of backcountry intestinal problems and (2) most backcountry watersources are fairly safe to drink, there is a wide variation in the critter content of water in both front-country and backcountry water sources. Some front-country sources are quite free of critters, while some backcountry sources are highly contaminated. Here in the SFBay Area, where we get much of our water from Hetchhetchy, our city water is minimally treated (well, ok, right now, there is a major maintenance project on the San Francisco water transport tunnel system, so a fair amount of well water is being added, requiring heavy chlorination by our standards - and it tastes bad, too - we are all praying for a rapid finish to the project so we get our pure mountain water back soon).
Personally, I have for years and continue to drink a fair amount of my water while in the backcountry directly from streams and springs. Not in Almaden Valley (site of a number of abandoned mercury mines), of course. And it is true that I spent part of my youth in 3rd world countries. So I may well have developed a certain amount of immunity. Still, I try to be very conscious of the situation with the water sources where I am.