Water Purification in the Backcountry
                            by Jeff Deutsch

[Updated]

Lately I have been purifying water with household bleach when possible.
Very cheap, lightweight, and effective.  Store it in a small dropper and
make sure the dropper doesn't leak.  Bleach will destroy nylon gear.  It
is especially dangerous around climbing gear.  The FEMA web site provides
these instructions for using household bleach:

   If you are unable to boil water, you can disinfect it using household
   bleach that contains 5.25 percent sodium hypochlorite. Chlorine bleach
   will kill some, but not all, types of disease-causing organisms that
   may be in the water. Do not use scented bleaches, color-safe bleaches
   or bleaches with added cleaners.

   If the water is cloudy, again, filter it and use the clear water for
   disinfection. Add one-eighth teaspoon (or eight drops) of regular,
   unscented, liquid household chlorine bleach for each gallon of water
   (one teaspoon of bleach disinfects five gallons of water). Stir it well
   and let it stand for 30 minutes before use. Store the disinfected water
   in clean containers with covers.

   Since liquid chlorine bleach loses strength over time, only fresh bleach
   should be used for water disinfection. For bleach that is one to two
   years old, the dosage should be doubled.

   Another method of disinfection is to use common household iodine from
   the medicine chest or first-aid kit. Add five drops of 2 percent U.S.
   tincture of iodine to each quart of clear water. For cloudy water, add
   10 drops and let the solution stand for at least 30 minutes.

[End of Update]


Disclaimer
----------
I'm not an expert on the subject of water purification or toxicology.
I have never even studied the subject except to collect the information
below.  This information may contain errors or omissions.  This information
is not a substitute for specific training or experience.  I assume no
liability for any individual's use of or reliance upon the information.


Contaminants
------------
The backcountry traveler has to worry about three classes of contaminants:

1) Viruses (ex. Hepatitis) - Very small microorganisms, on the order of
   0.004 microns.  These can't be removed by any available filter and
   must be killed.

2) Bacteria/Protozoa - Larger microorganisms which can be removed by
   a high quality filter or they can be killed.  Bacteria (ex. E. coli)
   are on the order of 0.2 microns while Protozoa (ex. Giardia,
   Cryptosporidium) are 5 microns or larger.

3) Toxins - Everything that is bad that isn't a microorganism (ex. lead,
   mercury, fertilizer).  Toxins can't be killed and are hard to filter.

How do you know if water is contaminated?  You don't.  So an absolute
rule in the backcountry is to assume that all surface water is contaminated.
Always have a primary and backup method of purifying water.

In December 2003, Backpacker Magazine published a report which leads me to
believe that there is only a slim chance of contracting any disease from
drinking water in the wilderness.  I believe that, but still don't see any
reason to take the risk when it is so easy to take precautions.



Methods
-------
Now that we have talked about the bad stuff, let's talk about the options
for getting it out of the water we drink.  There are many methods of doing
this.  Few methods remove all possible contaminants.

1) Iodine - Kills viruses, bacteria, protozoa except Cryptosporidium

   Long a standard method of water purification in the backcountry.
   It is lightweight, cheap and easy to buy.  Some people don't like
   the taste, but that can be removed with ascorbic acid (vitamin C)
   or masked with drink mixes.

   There are some questions about the health impact of long term use
   of iodine.  I haven't read anything definitive, so I consider iodine
   safe for a typical backpacking trip, but I would avoid it on very
   long trips (ex. a four month thru hike).

   However, there are some people who should not use iodine to purify
   water.  It should not be used by pregnant women, people with thyroid
   problems or people who are allergic to iodine.  This is a fairly
   common allergy.  People who are allergic to fish or seafood may
   actually be allergic to iodine.

2) Chlorine Dioxide - Kills viruses, bacteria, protozoa

   This is "the latest thing" in water purification in the backcountry.
   It has been used for years to treat municipal water supplies in Europe.
   It is supposed to be better than iodine because:
     - it kills all microorganisms (including Cryptosporidium)
     - there are fewer concerns with long term exposure/allergies
     - it is more effective over a wider range of temperatures

   Don't confuse chlorine dioxide with other forms of chlorine (like
   Clorox bleach).  They aren't the same.

3) Boiling - Kills viruses, bacteria, protozoa

   This is an easy way of purifying water with the drawback of using
   more fuel.  It is an excellent backup for most people since a stove
   is a common equipment on most trips.  If you are going to boil the
   water anyhow (like when making pasta) then just scoop it out of the
   stream and throw it on the stove.

   I've read differing opinions on how long water has to boil before
   all microorganisms are killed.  The consensus seems to be that as
   soon as it comes to a full, rolling boil it is safe to drink.  At
   high altitudes (where water boils at a lower temperature) I would
   let it boil for two or three minutes.

4) Picking clean water - Avoids toxins

   The basic thinking here is that it may be possible to reduce your
   exposure to toxins by picking good water.  It is generally considered
   impossible to identify water which is not contaminated with microorganisms.

   The tricks I've been able to learn for avoiding toxins include:
     - Pick clean, fast moving water.  Some toxins settle in slow water and
       others bind to mud and other particles in the water.  Avoid both.
     - Consider what is upstream of your water source.  Avoid taking water
       downstream of farms, landfills, drainpipes, etc.
     - Learn to recognize fish, plants and especially insects.  These are
       a good indicator of water quality.  Aquatic insects are especially
       sensitive to changes in water quality.  Generally, swimming fish
       are good, dead fish are bad.  Lots of algae might indicate large
       amounts of fertilizer runoff.  I don't know nearly enough about
       insects to even identify the type, much less determine what they
       tell you about water quality.

5) Filtering - May remove bacteria, protozoa, toxins

   Filters can remove contaminants.  Look at the absolute pore size
   (this is the maximum pore size) to determine which bacteria and
   protozoa they remove.  Any filter with an absolute pore size of 0.1
   microns should remove all microorganisms except viruses (no filter
   will remove viruses).  Toxins are generally filtered through some
   media like activated charcoal or carbon.  I don't know how to determine
   the effectiveness of toxin filters.

   Filters have to be cleaned or replaced on a regular basis.


Products
--------
We have talked about what contaminates water and what methods are available
to remove it.  Now lets summarize the products that are available to the
backcountry traveler.  I seriously doubt that this list is exhaustive.

The key to any of these products is to follow the directions closely!  A
filter is useless if you contaminate the output hose.  Iodine does nothing
if you don't let it sit for the proper amount of time.

1) Potable Aqua - Iodine tablets.  The directions tell you how much to
   use, how long to let it sit, and even how to make sure that the threads
   on your water bottle aren't contaminated.  Potable Aqua Plus adds a
   bottle of neutralizing tablets to remove the taste.

   I'm not a big fan of Potable Aqua.  I find that the tablets turn to
   powder over time (but I probably keep the stuff longer than you are
   supposed to -- when in doubt buy a new bottle).  It is cheap and
   lightweight.

2) Polar Pure - Iodine crystals.  A small lexan bottle with iodine crystals.
   You keep it filled with water which becomes a saturated iodine solution.
   You pour a measured amount of that solution into your water.

   Polar Pure is slightly heavier and slightly more expensive than Potable
   Aqua, but I like it more.  It is easy to use and lasts longer.  You have
   to provide your own taste neutralizers should you desire it.

3) Betadine (Povidone Iodine, a 10% iodine solution) - Often a component of
   your first aid kit, so it makes a good backup.  The general rule is 4 drops
   per liter of clear water and 8 drops per liter of cloudy water.  Wait at
   least 30 minutes and up to 60 minutes in cold weather.  If you have the
   betadine gel you will have to guess how much equals 4 drops.  Maybe a
   pea sized amount.

4) Aqua Mira/Pristine - Chlorine Dioxide.  Time consuming -- it has to be mixed,
   then allowed to stand, then added to water, then allowed to stand some more.
   Be sure to follow the instructions closely.

   The only place I've been able to find this stuff for sale is EMS.  I'll
   bet it is going to be more common in the future.  I believe that the two
   brands are identical.

Note: All of the above are chemical treatments.  They are all cheap and
      lightweight (relative to other methods).  They all require time to
      do their work, so you can't drink treated water immediately.

5) Pump filters/purifiers - Brands commonly marketed to backpackers include
   MSR, Pur, Katadyn, etc.  Note that a filter does not remove or kill viruses.
   A purifier contains an additional element (usually iodine) to kill viruses.
   Many filters and purifiers also contain activated charcoal or carbon media
   to improve taste and remove toxins.  Since iodine requires time to kill
   viruses, it is possible that using a charcoal or carbon filter will remove
   the iodine before it has killed viruses.  Read instructions carefully.

   These units must be handled carefully to avoid contaminating parts downstream
   of the filter.  Some are prone to breakage, leakage or blockage.  They are
   also heavy (relative to the chemical treatments) and costly.  Check the
   ergonomics of a filter before you buy.  Try using it to treat a few gallons
   of water.  Backpacker magazine had a good review of several models (see
   resources below).  Filter elements are field replaceable, with varying
   degrees of difficulty.

   In winter conditions, the residual water in a filter can freeze and cause
   the filtering element to crack.

6) Water bottle filters - Tiny filters in a water bottle spout.  This is
   the other "latest thing" in water treatment.  Exstream makes one.  I've
   seen another advertised that replaces the cap on a platypus water bladder.
   Some are EPA certified purifiers (I don't know what certification entails).
   That doesn't seem possible to me.  Even if you squirt the water through
   an iodine resin cartridge, the water goes immediately into your mouth.
   There is no time for the iodine to kill viruses.

   My gut reaction to these devices is skepticism.  I don't have anything to
   base that on.  It seems like if it were that easy then the bigger pump
   units would be serious overkill (and perhaps they are).  You might want
   to give them a try in the backcountry as long as you have a good backup.
   I'm not going to use one myself.  Maybe my opinion will change if I get
   additional information.

7) Steri-Pen - For the Sharper Image set to complement their GPS PDAs and
   cell phone watches (with integrated digital video capability).  This is
   an expensive little device that treats water with UV (ultraviolet light).
   My guess is that it very effectively kills bacteria, viruses and protozoa
   (but does nothing about toxins).  And it does so without adding chemicals.
   Drawbacks are that it only treats 16oz at a time and 4 AA batteries will
   only treat about 3 gallons of water.  It is also expensive.  Heavier than
   chemical treatments, but lighter than most pump filters (unless you need
   to carry a dozen extra batteries).

   So I wouldn't carry one.  I could see it being useful if you were doing
   the tourist thing in a part of the world where you didn't feel comfortable
   drinking the tap water.  But people who spend $200 for a gadget only drink
   Evian anyhow, right?

   It has got me thinking about filling a shallow bowl (like a frisbee) with
   water and leaving it in the sun.  After some amount of time the water would
   be purified by UV from the sun.  Right?  I'm not sure how well this would
   work, but I'd probably try it in a pinch.


Conclusion
----------
Based on everything I've written above you should be able to draw your
own conclusion.  Me?  I use Aqua Mira.  It does create better tasting
water than iodine (even with a neutralizer).  Though the taste of water
treated with iodine never bothered me much.  My backup treatment methods
are boiling and betadine (since I have a stove and first aid kit on every
trip).  On winter trips where I have to melt snow, boiling becomes my
primary means of water treatment (chemical treatments are less effective
in the cold).  I do my best to pick water which is free from toxins.

If I wanted the cleanest water possible I would use a pump purifier with
charcoal or carbon media.  But I don't want to carry that weight on a
regular basis.

How do you know if your water treatment works?  Hard to say.  In one first
aid class I was taught that 80% of the people who contract Giardia have
no symptoms or such slight symptoms that they never notice (I don't know
where that statistic comes from).  If you get sick one or two weeks following
a backcountry trip it might have been the water... or it might be something
else.  My dogs have been drinking out of streams for 10 years with no ill
effects (yes, yes, let's hear all your witty comments about my dogs), and I
would certainly drink untreated water rather than risk dehydration.


Resources
---------
  Backpacker Magazine, 12/96, p. 57 (followup 3/97, p. 14)
  Backpacker Magazine, 12/03, p. 45
  http://www.princeton.edu/~oa/manual/water.shtml
  http://www.rei.com/reihtml/LEARN_SHARE/camp/howfilter.html