I own a pump/filter (a sweetwater guardian) and have carried it on various trips with a "better safe than sorry" point of view. It weighs just short of a pound (13.5 ounces), and probably a full pound when the element is saturated with water. If nothing else, it is a convenient way to pump water out of small seeps and pools that are found at many springs in the desert mountains I spend time in.
I much more commonly just go ahead and drink, especially if the water looks good,
is moving, and there is no obvious source of contamination nearby.
I have never had any problems.
On my week long 2006 trip to the Sierra, I eschewed the filter and just used good old common sense! Does the water look good? Are we drinking from a stream that runs along a heavily used trail (especially if stock uses the trail), or is below where people are camping (or have been)?
The standard riot act reads like this: "Any water source, no matter how pristine it looks, and regardless of whether it is from a remote alpine lake or stream, may be contaminated with Giardia or Cryptosporidium." I am sure this is true, but it does sound suspiciously like a legal disclaimer invented by park service lawyers. You hear this statement, or a paraphrase of it echoed in almost every brochure and guidebook. Well almost every book ...
In Steve Ropers book, "Traversing Timberline Country", you can read the following statements:
"An optimist drinks Sierra water straight, without thought. A pessimist imagines that the same stream is teeming with death-dealing critters".
"In a 1984 study, scientists found giardia cysts in one-third of 69 tested Sierra lakes and
streams. Apparently once must ingest a minimum of ten cysts to have even a chance of
The highest concentration found in the study was 41 cysts in 100 gallons of water.
The next highest was 14 cysts.
"Both of these sites were heavily used ones.
... streams in high, remote basins have far fewer cysts than do lower streams.
Thus, the chance of contracting the disease up high seems virtually nil."
Steve Roper says, "On an anecdotal basis, this is further demonstrated. I have never had the disease, although for 40 years I've most often drunk the water straight."
George Durkee, a backcountry ranger in Kings Canyon Park for more than 20 years, has never heard of a giardia case.
Longtime Sierra mountaineer and giardia expert Bob Rockwell wrote me: "Most of the water in the Sierra has far too few giardia cysts for you to contract an infestation. Even if the water has many cysts you probably won't get the disease. If you do, you probably won't have any symptoms. If you get symptoms, they will probably go away by themselves in a week or so. If they don't or you develop serious and persistent symptoms, you should seek medical treatment".
In an article in Backpacker (Jaret, 2003), a number of wilderness sources were sampled and the worst Giardia concentration found was 1.5 cysts per liter, requiring at least 7 liters of water to be consumed to achieve a minimum infective dose.
It is surmised that one out of five people are asymptomatic giardia carriers. A recent article in the Journal of Wilderness and Environmental Medicine claims that a majority of giardiasis is caused by fecal-oral or foodborne transmission.
Mentioned in one of the articles was an "outbreak" aboard a cruise ship that was recently in the news. The water supply was just fine, but hygiene among kitchen help was the issue.
Morals of the story:
Carry soap or alcohol wipes for use after "restroom visits".
This discussion focuses largely on high alpine areas such as the Sierra Nevada. Multi-week trips (long distance hiking) would have other concerns (and would have to deal with more diverse and potentially contaminated sources). Virtually all sources along the Appalachian trail, for example, would have to be viewed as suspect since farm areas and livestock are present along most of the trail.
Symptoms usually begin 1 to 2 weeks after exposure, and may last 2 to 6 weeks. (This means for my typical 1 week backpacking trip, even if I get nailed by Giardiasis, it will hit me when I am out of the wilderness, not cripple me in the backcountry.).
Welch, T.P. (2000) "Risk of Giardiasis from Consumption of Wilerness Water in North America: a Systematic Review of Epidemiologic Data" International Journal of Infectious Diseases 4(2) 100-103.
Derlet, Robert W. (2004) "High Sierra Water: What is in the H2O?" Sierra Nature Notes Volume 3, April 2004
Welch, Thomas P. Evidence-Based Medicine in the Wilderness: The Safety of Backcountry Water Wilderness and Environmental Medicine, Volume 14, no. 4, 235-237.
Wood, T. D. (2008) Water: What Are the Risks REI Expert Advice, February, 2008
Jaret, P. (2003) "What's in the water?" Backpacker 2003, 31, 45-65.
Tom's hiking pages / email@example.com