Water filtering vs. purifying

This may have been answered a million times, but I can't seem to find any good info. I've done mostly short backpacking trips and always carried water. I'm interested in longer trips and want to know what is best...a filter or purifier. Any advice on which type and/or model will be appreciated.

Background:
-Mostly solo but sometimes group of up to 4
-Backpacking mostly in the mountains of MT,ID,CO,and UT

First thing is the difference between filtering and purifying. Purifying can be done by a filter that removes particles and organics to a sufficiently small size or by chemical means. Filtering is just the removal of particles and organics.

A filter can let through viruses (a large fraction of the filters on the market), while catching bacteria and protozoa. Most filters do not remove chemical contaminants (many of the streams in the local hills have runoff from the now-abandoned mercury mines in them, to the extent that the fish caught in the streams are dangerous to eat). Filters that contain activated carbon can remove much of the chemical contamination, although they do not remove all varieties of contamination. For example, they generally do not remove salts. There are filters, known as reverse osmosis filters, that will desalinate. Filters will also remove silt (but this can clog filters very quickly). Some kinds of organics (certain chemicals from algal blooms, for example) are not removed by filters, although carbon filters can remove them.

Chemical treatment is primarily use of halogens (chlorine and iodine). Halogens will kill all organisms (protozoa, bacteria, viruses) if left in contact with the water in sufficient concentration and for sufficient time. Since it is a chemical reaction, "sufficient time" depends on the temperature of the water. In some cases, this can be several hours. Some people react badly to iodine, and use of iodine for long periods (month or more on a daily basis) is generally not recommended. Many people do not like the taste of either chlorine or iodine in their water, which is why some chemical treatments come with a neutralizer that removes the taste (have to leave the treatment in there long enough for it to be effective). Chemical treatments do not remove chemical contamination.

Boiling (actually, just raising the water to greater than 150F) will kill all organisms. It will not remove chemical contamination, nor will it remove silt. Some algal blooms, being mostly chemical contamination, also are not affected. Some protozoa and parasites have a cyst form when dormant that requires keeping the water above 150F for a longer period. Note that water will boil above 150F at all altitudes you can hike to. It has been shown in a number of studies that it is not necessary to follow the old advice of "full rolling boil for at least 5 (or in some older books, 10) minutes". The organisms are killed by the time you reach 150F. Big problem with boiling is that it takes fuel. However, you do not have to filter or chemically treat the water you use in cooking if you are boiling it anyway.

The answer to your question is that it depends on where you are getting your water. Aesthetically, you may want to do something to get the cloudy appearance out of the water. Whether you use a filter pump or a chemical pill, you may want to pre-filter by (1) letting the water stand still for a while to let the silt settle out for a while, then decant it (or pump from above the settled layer) or (2) use a coffee filter paper to pour the water through first. Then use a filter pump with its pre-filter (helps slow the clogging). This gets the water free of the nasty organisms, except possibly viruses (depends on the brand of filter - read the websites of the manufacturers). You can further remove the viruses if you use one of the filters that has an iodine resin or putting a halogen into the filtered water.

Actually, in most of the US and Canada, plus western Europe, a basic filter like the Katadyn Hiker or MSR Miniworks or MSR Sweetwater is just fine (I do suggest prefiltering the water with a coffee filter to get most of the silt out first). If you are going to 3rd World countries, you will want to do something more extensive.

My favorite method is to treat water with equipment you already have.

Boil the water. Rapid boil for 30 seconds.

Water can be filtered with cheap, light weight coffee filters before boiling.

All just a matter of preference.

The areas which you specifically mention have fairly good water in the woods and hills. However, some of the streams have a lot of silt, either because the soil is glacial flour (the superfine dust that results from former or present glaciers grinding it "exceedingly fine") or is volcanic ash. You will want to pre-filter with something like a coffee filter.

For the most part, in those areas you don't need to worry about chemical contamination from mines. In Colorado and Utah, for example, most of the mining was done before chemical leaching was done on a large scale and most of the processing of the "hard rock" was done at mills that are near present highways, which is not where you are likely to be backpacking.

If you were in Montana, on the other hand, where there are lots of current open pit mines, you would have to worry about chemical contamination.

Regular filter pumps are adequate in the areas you name (once you get the silt out with something like a coffee filter), and will remove the protozoa, parasites, and bacteria. You don't have much in the way of viruses once you are in the backcountry.

Contrary to what Ed implies, coffee filters do not remove any of the organisms like giardia or campylobacter. Heating to above 150F is adequate. Boiling is not necessary, according to the wilderness medicine journals with refereed articles, although in the absence of a thermometer, heating to the start of boiling guarantees you got to the 150 mark. If the 150 mark were not adequate, then FDA recommendations for cooking meat would not be minimum 145F (for beef) and 170F for boneless poultry. Oh, ooops, I forgot. Ed is a S'thnr, and they believe steaks aren't cooked until they are charcoal and leathery. Ok, if you are from the South, you better boil everything, or better yet, deep fat fry it (hmmmm, deep fat fried water -- there's a strange thought).

Nope. Nope. Nope.

I never implied that coffee filters would take out micro organisms.

I recommend coffee filters to filter dirt and sediment out of water prior to boiling.

In my opinion all one needs is a stove and on rare occasions coffee filters to treat water.

I personally think purifiers and such hardware are a waste of weight and pack space. I can treat four gallons (+/-) of water on one 470 Camping Gaz can

Oh, I forgot to add:

I'm not a Southerner.

I live in Florida, I was born and raised in the Pittsburgh area (Bethel Park).

Guess you would call me a "Burgher".

Actually, Ed, some people actually will read into your sentence that all they need do is use a coffee filter. I know they do this, because we have had several people over the years in the Outdoor Awareness course say exactly this after the section on water and sanitation. Now, this is always hard to believe, especially since OutAware is the *advanced* backpack course, intended for folks going to lead 50-milers, supposedly coming into the course fulfilling the stated prerequisite "extensive backpacking experience". And, yup, same group that all too often has folks who can't light their backpacking stoves.

Sometimes it seems I never learn to be very careful and very explicit in giving the advice (witness the "knees" post, where Jim chided me rightfully for forgetting to mention some basics that I often assume "everybody" knows).

Anyway, on boiling as a preferred method - I agree that boiling (or rather heating to the 150F+ mark) is pretty much guaranteed and easy to do. Filtering out the junk with something as simple as a coffee filter is more for the aesthetics, but then, who wants to drink muddy water, even if it has the organisms killed, and who wants sticks and sand in their Pasta Appalachia? However, boiling does not remove chemical contaminants (most filters don't either, except ones with activated carbon elements or add-ons like the one that Katadyn is now selling).

More important, on a long trip, fuel is precious and it is heavy. You really do not want to waste fuel when you are spending a month or two in the Alaska Range or the Andes, nor even through-hiking the AT or PCT. 4 gallons on one 470 canister? Well, 4 gallons is roughly 16 liters, which is 2 to 3 person-days of water at the recommended intake for hiking with a pack, whether summer Sierra or Smokies or at altitude in the Andes, Alaska Range, or Himalaya. A full 470 canister is about 1.5 pounds, vs a Sweetwater filter, for example, at about 1 pound, and you have to pack the empty half-pound of empty canister out. A typical filter can treat several hundred gallons of water (assuming you use a coffee filter, settling, etc to remove silt so it doesn't clog rapidly). If I go on a week-long backpack solo, I will need 2 or 3 470 canisters, by your numbers, just for purifying water, and carry out 1 to 1.5 pounds of waste metal (the empties), starting with 3 to 4.5 pounds. I am not including the fuel needed for cooking my meals, of course, which in summer should only take one more canister that I would have to have anyway. With the filter, I start with the 1 pound filter (rather than 3 to 4.5) and carry out the same 1 pound filter (rather than 1 to 1.5 pounds of waste metal - well, here in Palo Alto, the canisters can be recycled, although in most of the world, they just end in landfill).

And if Barbara goes with me, double the amount of canisters needed, where with the filter, I still use the same 1 pound filter. Add Jim and his latest hiking companion brings the group up to maybe 15 pounds of canisters, with 4 to 6 pounds of waste metal, vs the filter, still at 1 pound for the whole group.

Add in the environmental cost of that CO2 resulting from the burning of the butane and extraction of the natural gas, and it looks to me as if boiling is a very inefficient way of treating the water for the backpacker (yeah, yeah, I know, the filter is made of plastic, which is a petroleum derivative. But it is a lot longer lived)

4 gallons of water is about 16 liters, as I said. But the recommended rate of fluid intake when doing vigorous exercise (hiking in the Sierra or Smokies, thrashing your way up high mountains) is about 4 liters a day, which means Ed's 4 gallons is about 4 person-days of water to be treated rather than the 2-3 I stated. Let's go with the 4 person-day rate (yeah, I know, some people get along with just a cup of water per day). So the corrected version follows:

A full 470 canister is about 1.5 pounds, vs a Sweetwater filter, for example, at about 1 pound, and you have to pack the empty half-pound of empty canister out. A typical filter can treat several hundred gallons of water (assuming you use a coffee filter, settling, etc to remove silt so it doesn't clog rapidly). If I go on a week-long backpack solo, I will need close to two 470 canisters, by your numbers, just for purifying water, and carry out a pound of waste metal (the empties), starting with 3 pounds. I am not including the fuel needed for cooking my meals, of course, which in summer should only take one more canister that I would have to have anyway. With the filter, I start with the 1 pound filter (rather than 3 pounds of full fuel canisters) and carry out the same 1 pound filter (rather than 1 pounds of waste metal - well, here in Palo Alto, the canisters can be recycled, although in most of the world, they just end in landfill).

And if Barbara goes with me, double the amount of canisters needed, where with the filter, I still use the same 1 pound filter. Add Jim and his latest hiking companion (4 people for 7 days is 7 canisters) brings the group up to maybe a bit over 10 pounds of canisters, with 3.5 pounds of waste metal, vs the filter, still at 1 pound for the whole group.

Add in the environmental cost of that CO2 resulting from the burning of the butane and extraction of the natural gas, and it looks to me as if boiling is a very inefficient way of treating the water for the backpacker (yeah, yeah, I know, the filter is made of plastic, which is a petroleum derivative. But it is a lot longer lived)

So, the conclusion is still the same - the filter is much lighter and more environmentally friendly than boiling to purify the water. Even if you claimed that you only had to count water drunk as water and got down to 2 liters per person per day of drinking water, you are ahead in weight for one person at one week, and way ahead with the filter when you add that second, third, fourth person. And, by the way, you really do have to count more than just the one trip for your usage in terms of the CO2 produced and the waste metal empties.

Did you post something else? I still haven't had the two days it takes to get thru the first one :).

I say and always will say, just boil the freekin' water. If the water isn't clear, filter it thru coffee filters BEFORE boiling.

direct, to the point and only two sentences. I don't believe that can be misinterpreted.

and yes Bill, I still love you even though you insulted me with that southerner crack.

Truth is, I happen to deep fry everything under the sun in peanut oil. When the oil is cooled off, I use it to moisturize the black plastic trim on my car.

Ed (the 'Burgher)

Bill, that's the Pittsburgh in Pennsylvania.

I don't know, Ed. I'm with Bill on this one, with a couple exceptions:

1) Winter, when liquid water is hard to come by. (Around here anyway.)
2) Short trips (1-2 nights) where you're carrying more fuel than you'll use just for cooking. (though I usually pump even then)

The other big problem with boiling your drinking water is that it's hot. Hot water is good in winter, but not so refreshing when it's 90 and humid.

Here's an interesting water filter/purifier I found on the web. http://www.aquapuretravel.com/
I don't think they are for sale here in the U.S. yet, but it seems to filter out almost everything, including some heavy metals (there's a chart on the website). It does use Iodine as part of the purifier so that may be a drawback over time. It seems to be aimed at people traveling in Asia or Africa where clean and safe water is often not available.

Dave and Bill, LOL! I think the point of my original post was lost about 10 kilometers back.

I just stated what MY favorite method was. Just stating my opinion. I am in no way preaching that boiling is the only way.

If someone wants to carry a still on their back, hey go for it! That is their preference.

________________________________________________________

"My favorite method" is to treat water with equipment you already have.

Boil the water. Rapid boil for 30 seconds.

Water can be filtered with cheap, light weight coffee filters before boiling. ("can be" is not implying "must be")

"All just a matter of preference." (Opinion)

Yeah, yeah, Ed. I know, you claim to be a 'burgher [my father was born and bred in Universal (Plum Township, virtually in downtown Pbrg, but way out in the sticks when he was born) and lots of the relatives - typical family of 10+ kids in those days - still are around the area]. But you have been in Cuba, er, I mean, N'Yoahk South, ummm, I mean, Florida long enough to be thoroughly contaminated. Peanut oil, eh?

But, gotta admit, we lived in Mississippi for 10 years, having gone from Arizona where I grew up (except for brief stints in Virginia and Honduras), to California (where Barbara was born and grew up) to Boston to Mississippi. And while our neighbors, native Mississippians all, were very friendly, we were always Yankees to them. Couldn't convince them that "Yankee" is someone from Maine.

No, your point was made. But some folks don't always read things completely. So it is important to point out very explicitly, as you did subsequently, that the coffee filter is used as a pre-filter.

But, again, it is not necessary to boil for 10 min, 5 min, or even 30 sec (your number). The medical tests say that getting the water to 150F is sufficient to kill all organisms, which is achieved before reaching the boil point at all altitudes you can hike or climb to (getting close at the summit of Everest, though).

The disadvantages of boiling:

1. As Dave said, the water is hot - ok for your coffee, tea, hot chocolate, or whatever you are cooking

2. uses extra fuel, and lots of it

3. does *not* remove heavy metals or other chemical contaminants, including the organics produced by some of the organisms, such as some algaes.

Thanks to Tom for pointing out the web site for the Aquapure Traveller. However, the marketeers have done a bit of distorting of the facts (to be expected - "OUR product is better than anyone else's!). They make a flat statement that no pump filter gets rid of all organisms incuding viruses. But they noticeably omit some very important viruses from their effectiveness list that are found in the water in 3rd world countries (most notably the hepatitis family). Boiling will kill these. They also state that iodine will not kill certain bacteria and protozoa that in fact are listed as being killed by iodine and chlorine in, for example, Paul Auerbach's huge Wilderness Medicine book (considered the most authoritative wilderness medicine reference).

It is really interesting that they list the heavy metals that are removed. I suspect that other activated carbon filters (which is how the Aquapure Traveller works) do the same - Katadyn Hiker and Hiker Pro and their add-on carbon container, Sweetwater, to name a few. But at least Aquapure Traveller does provide a list. I was a bit perturbed by noting that while most of the metals are listed at 90 percent removal or more, arsenic is listed at 17 percent. I presume this is a misprint (there are several obvious typos in their pages), but that is very worrisome for some of the streams around here that have runoff from old mines, and even some parts of the western foothills of the Sierra. At least the mercury is listed at >99.25 (doesn't help with the fish caught from the streams in Quicksilver Park, though).

Dave is right about filters being a problem in winter. If you don't get all the water out of the filter and it freezes, the expansion of the water as it turns to ice can crack the filter, in which case, no filtering. In winter, when I have to melt the snow, it is just as easy to heat the water to the 150+ point, so I generally don't even take a filter for those conditions. Hey, it takes 80 kcal per liter to turn the ice into water and another 100 to get a full boil, needed for the hot cocoa and for the cooking anyway.

A staff member on my winter course works for a company that distributes filter bags that go down fine enough to filter most viruses, and at a rapid throughput. He gave all of us on staff samples. But I haven't been brave enough to pour known contaminated waste water through one and drink it.

I don't claim to be a 'Burgher, I am a 'Burgher.

In fact, I still own own a house there.

Ok Charlie Brown, I'll go with this recommendation to anyone and everyone:

Buy that expensive and heavy water purifier.

Purify the water.

Then boil the water for 30 seconds!

e

The First Need water filter removes chemicals, bacteria and even viruses. And it does it without adding chemicals. I don't know of any other filter that does that.

The system I normally use is HTI's X-pack. It is a forward osmosis system and I've used it is some horrible conditions taking some very putrid water and making it drinkable. I have friends who have used it in Afghanistan and Iraq and have even had to use it to filter urine. They do not have a system for salt water yet but they are working on packs that will filter saltwater for use on US Navy submarines. The company is solid and the people they have working for them are top notch. They may be back ordered for some time because of the hurricane damage but they definitely make a quality product.

Looking at their website, the X Pack appears to be very good, but very expensive and slow. $64 for something that lasts only 10 days and filters only 40 liters doesn't seem practical or affordable for the average backpacker. Plus you have to make a energy drink out of it for it to work. For the military or other government agency spending someone else's money, sure, why not. I doubt most aid or relief agencies could afford it either unless they get a break on the price or are selective in its use.

Hey all, I'm just curious. I know this was really thrashed over a couple of years ago but I never got a completely clear picture of what most people do in the US and why. Under what conditions do you filter/boil/purify water? Do you ever just drink it straight from the stream? From experience around here (Australia) I don't know anyone who routinely treats water in the backcountry and now I think about it I actually can't think of the last time I did, it was probably years ago.

I suppose what I'm asking is if you do always treat your water, why do you do it? (because 'they' say to??). Do you only treat sometimes? If so, what makes you decide to? Never treat...ever get sick?

I typically get my water from springs and natural sulphur wells.... so do the local critters and they aren't polite enough to poop 500 feet away from the water source.

Therefore I purify.

Years ago, we used to just drink from the streams, and sometimes even watersources that had obvious red flags (like beaver dams - giardiasis is sometimes called "beaver fever"). In the Sierra and Rockies, until the explosion of backpacking, the water seemed to be pretty safe as long as there were no obvious signs of livestock (the horsepackers and cattle). But somewhere in the 1960s, there were water quality tests starting to be run in backcountry areas that were popular (since there was a growing incidence of disease) and it was found that there were many streams and lakes that had contamination.

So most people these days do something to sanitize the water most of the time - boil, filter, chemical treatment.

It seems that things like giardia are being picked up by the wild animals and carried into the farthest reaches of the backcountry all over North America, plus with the large backcountry population, many backpackers do not practice sanitary disposal of human and other waste.

Remember that the population density of Oz and Kiwi-land is much lower than the US. Plus fewer people get into the backcountry. and NZ has the hut system with many having outhouses. At the same time, many of the water-borne ailments take several days to a week to develop. So many of the cases of giardiasis, for example, or Norwalk virus do not show up for a week or so, and there is a lack of association with the backpacking trip ("must have been that fast food restaurant yesterday"). Since a lot of the symptoms resemble flu, it also can get blamed on something else.

"Plus fewer people get into the backcountry. and NZ has the hut system with many having outhouses."
Not sure that fewer people hiking in NZ is the answer because plenty of them do, but the hut system definitely helps. Also, NZ has no large native land mammals, just indroduced deer and thar (mountain sheep)up high so once you are above the sheep, the water is presumed to be safe. I drank it all the time in the bush and never got sick once.

Hey Bill and Ed, If I'm reading you right, both of you say that the main reason why you treat water is because you're getting rid of bugs (in particular, Giardia) that are from wild animals(?) I have never been able to find reliable scientific data that there is a real risk of catching giardia from wild animals via contaminated water (and I've done a fair bit of digging over the years). Lots of speculation of course, but nothing solid. Of course, as the saying goes, an absence of evidence of something does not mean evidence of absence...

If you do know of specific info I'd appreciate it either by posting or by email...

Cheers,

Andrew

Andrew -

Historically, beavers apparently harbored giardia at least since colonial times. The increase in various bacteria, viruses, and protozoa starting in the 60s in the Rockies and Sierra found in the streams and lakes is mentioned in several of the standard books (e.g. Paul Auerbach's big book on wilderness medicine). Auerbach's smaller volume says (p 190) that giardia is found particularly in "wilderness settings in the western United States, ..." and that the cysts are present in the feces of "humans, elk, beavers, deer, cows, dogs, and sheep." Major contributors are the large number of backpackers who don't seem to understand wilderness sanitation and the large number of horse, mule, and llama packers (these animals appear to be carriers as well and don't care if they are standing in a stream.

Whatever the carriers, there have been numerous samplings of the water at various locations. Unfortunately, these are not systematic or anything resembling regularly scheduled. Some streams close to trailheads show up as heavily contaminated one time, then a few months later are as pure as distilled water. Some high country streams and lakes test contaminated, some quite pure. There is really no way to tell for any given stream. The Wilderness Medicine Association publishes some of these studies almost once a year in their journal. I think you can get them on line even if you aren't an MD or a member. I see them because a friend who directs our scout leader high adventure backpacking courses gives me copies from time to time.

As I previously posted, I don't seem to have any problem. But then I even eat the food and drink the water in Mexico and Central America and never have a problem. On the other hand, I have been with people who got very sick in the Wind Rivers and Colorado Rockies.

Hey Andrew, I don't know anything really specific about water borne bugs, I just don't like the idea of drinking armadillo poop tea.

Therefore I purify

Hey Andrew, I don't know anything really specific about water borne bugs, I just don't like the idea of drinking armadillo poop tea.

Therefore I purify

and I feel strong enough about the subject to post it twice.

Yep, when the critters (horses, deer, wild boars, alligators. racoons and panda bears) all stop to take a drink in my well, they all seem to want to leave a little valentine just for me.

Turds are great in my garden but I really don't like 'em between my teeth.

Bill, There was an article in the Outdoors section of the LA Times a few weeks ago about water contamination in the Sierras. I thought I'd saved my copy, but apparently not. A researcher from UC Davis was hiking around and doing water tests. His conclusion, as I recall, was that the fear of contamination was greater than the threat. The article is probably online, but I think you'd have to pay to read it.

However, if you're the one who gets sick, who cares what the odds were that it would happen.

Found a link to the story:
http://www.latimes.com/travel/outdoors/la-os-giardia26jul26,1,2328505.story?coll=la-headlines-outdoors&ctrack=1&cset=true

Hi Bill,

I do have access to the scientific literature and have done searches several times over the years (sometimes as part of my work) looking for any good published data on the risks of drinking backcountry water. The only evidence that seems to be out there in the mainstream scientific literature linking backcountry water to parasite infection and diarrhoea could be most generously described as 'flimsy'. I keep thinking I must have missed some key piece of research somewhere (which is why I asked you...you seem to have contacts in all sorts of outdoor areas) but so far nothing has turned up that is convincing. To be clear, I'm talking about water from non-high use areas, not from heavy-use areas or farmland, there's not much doubt that you can get Giardia or Crypto under those conditions.

Most stuff written in wilderness texts argues, often implicitly, something like: "Giardia (or crypto) are found in backcountry water, Giardia (or Crypto) causes diarrhoea, therefore drinking untreated backcountry water will make you sick". But this is not the same as having evidence saying "drinking water in the backcountry makes you sick". Quite simply, there are very few studies that directly address this, and most of those are so badly designed and interpreted that to all intents and purposes they're meaningless. Even if you do accept the most 'reliable' reports, their figures only suggest a tiny increased risk. One of the main reasons why there is such a mess in the studies is that no-one is even really sure how many species of Giardia or Crypto there are and how many of these species can infect humans. Until very recently, when Giardia or Crypto were identified in environmental water samples they were assumed to be transmissable to humans, but a lot of studies that have come out recently have questioned if this is actually true.

It's hard to distill a lot of reading, discussions and experience into a couple of paragraphs, but my personal belief is that at the very least the level of paranoia that surrounds water treatment is totally out of proportion to the actual risks, so I chose to drink backcountry water unfiltered. (For Ed G: with poop and all!)

Tom, I finally went through the registration procedure for the LA times and got to look at the article. Very interesting indeed!

Although I might be biased :)

Tom -

Thanks for the link. Yes, that's one of the things the MDs we have doing the medical part of our backcountry courses have had to say. They also note that it is hard to tell whether a particular water source is ok or not, and that some people seem to be a lot more susceptible than others. As I said, I don't seem to be susceptible, but others on the same trip have sometimes gotten very sick. Some years ago, I hooked up with a guy to to the Exum Direct. By the second pitch, he was suffering so much from the giardiasis he and his girlfriend had picked up in the Winds a couple weeks before that I ended up leading the whole rest of the climb.

I tried to click the "print" button on the article, but it wanted me to sign in. I was able to just print with the regular Firefox print function, though. Any idea how long these links stay active? I would like to add it to our list of links for the backcountry courses.

Andrew -

I agree that it seems to be high use areas. Unfortunately, that seems to include most of North America these days, although the population density in the Sierra seems to have dropped in the past 10 years or so (maybe thanks to the limits and permitting system???). Hasn't dropped much if any in the Colorado Rockies or Wasatch, though.

As Tom noted, doesn't matter much that the odds are small of getting something, if you are the one who wins the lottery. And I gotta wonder if maybe people's immune systems aren't getting a bit compromised by "modern" living conditions - fast food, air pollution, too much time sitting at the keyboard, and such (I try to get out for a 5-10 mile hike or 30 mile bike ride every day to compensate for my advancing years, plus growing up in a small village on an Indian reservation in the middle of the Arizona desert - maybe that helps me a little).

-- Bill, (aka The Old GreyBearded One)

Here is an interesting article regarding Giardiasis that also has a lot of references to other published studies. I have not read the LA Times article mentioned above so I don't know if this is some of the same information.

Regards,

Tom Williams

Bill, I don't know how long the links stay active and free. I read the New York Times online too and their stories only stay free for about a week before being archived and become the equivalent of pay per view. I was surprised to see the link actually working. The LAT site is clunky and the registration is a pain, but it's free for now. I'm a print subscriber and I still had to do the whole registration thing.

BTW, there are many other discussions about water on The Lightweight Backpacker website's forum pages (www.backpacking.net) Look for "communities" on the home page. You have to register to participate, but it's easy. Jim S posts there quite frequently and as you might suspect, manages to raise a few hackles every now and then.

http://www.backpacking.net/forums/ubbthreads.php?Cat=

This should be the direct link.