Water Purification – The Facts

First the disclaimer: The post below is my opinion only and I am not responsible for any injury or illness you may suffer from drinking improperly treated water. I did my research, but what do you really know about my research abilities? I could be near-sighted and insane for all you know. This is not meant to be a substitute for your own work.

When it comes to drinking water in the backcountry, there are 5 major threats:

1. Chemical – usually herbicides and fertilizers from nearby farms, occasionally plain old pollution.
2. Giardia cysts – these are 6-10 microns in size
3. Cryptosporidium cysts – these are 4-7 microns in size
4. Other random bacteria – size varies widely, but can be as small as .2 microns (E.Coli, Salmonella, and Cholera)
5. Viruses – size varies widely, but most are less than .1 micron (hepatitis A, rotovirus, polio).

In the United States there is a terminology difference between “filter” and “purifier.”  A water filter will remove Giardia and Cryptosporidium as well as some other harmful bacteria (depending on the pore size).  A purifier will remove viruses as well.  I’m not sure if this same terminology difference holds true outside the U.S. or not (i.e., it may be an industry defined term and not a government defined term).

There are 5 commonly used purification techniques:

Boiling – bring the water to a boil hold it there for some period of time.  There is a lot of debate on this and people try to bring in altitude and many other factors.  Here’s the bottom line: 212 degrees fahrenheit/100 degrees Celsius, for 1 minute will kill of anything living in the water (bacteria, protozoa, viruses — collectively called “critters”).  Just be aware that water may reach a rolling boil at temps well below 212 Fahrenheit at high altitudes, so continuing to add heat and boiling for longer is advisable.  Boiling WILL NOT eliminate many chemicals and may actually concentrate them further.  As one article I read worded it – “if there are harmful chemicals in the water, boiling will just make them warm harmful chemicals.”   That said, boiling is probably the safest (as in most foolproof) method for removing “critters,” but it does have a few significant disadvantages.  1) It takes time, effort, and materials you may not have; 2) If the water was dirty as well as contaminated, it will still be dirty after boiling; 3) the water will taste “flat” after boiling.  This can be remedied by pouring it from one container into another; 4) as mentioned previously, it WILL NOT remove chemicals; and 5) if the water tastes bad before boiling, it will likely still taste bad afterwards.

Chemical Purification – the two most common methods used are iodine tablets (available from Aquamira) and chlorine dioxide tablets (available from Katadyn – called MicroPur).  Both work well against viruses and bacteria, including giardia.  Iodine WILL NOT work against cryptosporidium.  Chlorine Dioxide will (though it takes 4 hours).  Chlorine Dioxide and household bleach ARE NOT the same thing.  Household bleach is sodium hypochlorite.  Chlorine dioxide is…well…chlorine dioxide.  The two are not interchangeable.  In fact, cryptosporidium has been shown to survive a 24 hour immersion in 100% bleach and still be healthy enough to infect a human.  Not so with chlorine dioxide.  Moreover, using bleach to purify your water can be risky as different types of bleach contain different percentages of the purifying chemical.  Downside to iodine: 1) funky taste, odor, and color in the water; 2) ineffective against cryptosporidium.  Downside to Chlorine Dioxide: it takes 4 hours to work against cryptosporidium and 30 minutes to work against everything else.  Downside to both: 1) performance is affected by water clarity and temperature; 2) they take a good deal of time to be effective.  On the upside – Chlorine Dioxide is actually known to improve the taste of backcountry water.  I can vouch for that firsthand.  It makes it taste…clean, but not like bleach or other chemicals.  I have no idea why this is true.

Filtration – Filters have the added benefit of removing “crap” from water.  Dirt, sediment, and other things that affect water taste and clarity go away.  I won’t go into the difference between membrane and pore filters, but I will say that membrane filters are generally longer lasting and capable of more precise filtration at a smaller micron size, but unless they incorporate an activated carbon stage, they are ineffective against chemical contaminants.  If you see a filter like those made by Sawyer that says “lifetime guarantee” or “no replacement filters,” it’s probably a membrane filter.  Those can be backflushed and reused indefinitely.  There are hand-sized filters of both pore and membrane type on the market ranging in filter size from 4 microns down to .2 microns and in price from $20 to well over $200 (and counterintuitively, micron rating doesn’t determine the price).  Generally, in a filter, you want to minimize pore size (smaller is better) and if chemical contaminants are a concern, you want an activated carbon component somewhere in the process.  I’m going to deal with the specific examples I have experience with and describe the pros and cons.

Aquamira Frontier Pro is a pore filter with pores that are more than 99% effective against giardia and cryptosporidium that are 4 microns in size or larger.  Looking at the sizes I mentioned above, that means it will handle giardia and the vast majority of cryptosporidium, but not viruses and many bacteria will sail right on through.  Careful water selection is key here.  The product website says it does have a carbon filter stage as well (though they never use the keywords: activated carbon), so it should be at least somewhat effective against chemical contaminants.  It needs to be replaced every 50 gallons (200L), but at $25 per unit, that’s very doable.  It takes up very little space, weighs 2 oz dry, it can function as a direct drinking straw, can be attached to a water bladder, and can be used in a gravity filter mode (though it IS slow).  In short, it’s versatile, affordable, and functional as long as you understand its limits, but the limits are serious.

Katadyn Hiker Pro – at one time this was the single most popular model out there.  It costs about $80, weighs about 11 oz and takes up about the same size in your pack as a 20 oz Nalgene bottle.  It’s a hand pump type filter, with a 200 gallon (750 L) capacity before needing to change the filter cartridge ($40 per replacement).  It comes with attachments that allow you to use it in a number of ways, but gravity filter isn’t one of them.  It’s a pore filter with a .3 micron pore size (that will the vast majority of critters, but not viruses or the smallest bacteria).  It does have an activated carbon core, which should cover most chemical contaminant issues.  The main downside is that it can be a pain to use.  The pumping action is violent and tends to kick up sediment from the bottom in shallow water.  Your filter then has to take out that sediment and that shortens your filter life.  It’s also really tiring to use the hand pump after a day of backpacking.  A typical 4L basecamp setup is going to require constant pumping for 4-6 minutes with a fair amount of resistance (depending on how new the filter is).

Platypus Cleanstream Gravity Filter – I reviewed this HERE, so I won’t cover it again.  HERE is another review.  This is .2 microns (covers all critters except viruses), and DOES NOT have an activated carbon stage in the filter (will not eliminate chemicals).  Downside: doesn’t eliminate chemicals.

Ultraviolet – there are probably other systems out there, that do this, but the most well known is the Steri-pen.  Tiny and costs about $90 before accessories.  Basically, you put the “pen” (it’s actually about the size of a large car key) into the water, push the button and hold for however long the manual says…I believe it’s a minute, but don’t quote me.  The device is effective against critters, but not chemicals.  This would be an AWESOME product for international travel, but when it comes to camping, I don’t own it for one main reason: it requires electricity and that, to me, is just dumb.  I am not going to depend on electricity or batteries for something as important as water when I’m 10-30 miles away from civilization.  I’m not trusting my life to my memory if I can avoid it.  The company, to their credit, tried to address this concern with a solar charger.  It takes something like 20 hours of hardcore sunlight to get a full charge (the company calls that 3-5 days).  Inadequate and unacceptable.  Notably, I can no longer find this product for sale on the Steripen site, though it is available at several other places online.  Another concern is that it only works properly if the water is clear.  The company did address this concern well – they now have a prefilter that will attach to virtually any type of bottle or bladder.  That cleans the water, then the steripen purifies it.  One more downside: if the water tastes bad before purification, it will still taste bad afterward.

Mixed Oxidant – the MSR Miox is the shining example.  $140 and tiny.  Works very quickly.  The process is a bit complicated, and here again, it requires electricity.  Basically, chemicals are combined (in the unit) with salt and water in a very small dosage (exact amounts depend on the amount of water and the pH balance).  That solution is then electrified and poured into the water you intend to drink.  You shake it up and poof, the water is “pure.”  That’s about all I know here.  It’s effective against critters but not chemicals, and I rule it out based on cost, the need for electricity, and the fact that the process is too complicated for me to trust myself when I’m tired and dehydrated.

So what’s the best option?  In my opinion, the dream system would be small, lightweight, gravity fed, less than 1 micron in filter size, electricity free, and effective against viruses, bacteria, cryptosporidium and giardia, and chemical contaminants.  It would also be affordable.

The only way I’ve found to even come close to this is via a combination of filtration and chemical treatment.  Specifically, filters and chlorine dioxide combined are an amazing choice.  You eliminate the 4 hour wait time for the chlorine dioxide to kill off cryptosporidium because the filter takes care of the cryptosporidium for you.  That means you only have a 30 minute wait time to kill off remaining bacteria and viruses.  If you have a filter size of less than 1 micron, then you are down to a 15 minute wait to kill viruses.  If you aren’t in an area where viruses are a concern, you’re down to zero wait (at this point, the chlorine dioxide tablets are just for flavor and aren’t really doing anything in the way of purification until after 15 minutes).

If I’m near a farm or using a metropolitan water source, then I’m at risk from viruses, bacteria, and chemical contaminants.  Therefore, I’m going to use my platypus gravity filter, chlorine dioxide tablets, and a katadyn carbon filter attachment in combination and choose my water from a clean, moving water source that I’ve scouted upstream for at least 100 yards (or ideally, find the source and take from that).  This way, I’m safe from chemicals and critters both.  I’m also going to give the water a full 30 minutes of wait time after treatment.  Overkill? Maybe. Worth it?  You tell me: cryptosporidium can lead to diarrhea, vomiting, nausea, and headaches for 2-10 days straight.  Giardia is similar but lasts for 2 to 6 weeks.  Both can be fatal.

If I’m in a more pristine wilderness, I’m still going to choose my water source carefully as described above.  I’ll just drop the carbon filter attachment.

I do carry the Aquamira Frontier Pro in some situations – a dayhike, for example.  I’m willing to make the micron trade-off for a hike when I’m only a few miles from civilization.  I’ll still bring and use chlorine dioxide.

There are “pre-combined” purification systems.  Most incorporate a filter and chemical treatment in a squeeze bottle setup.  These undoubtedly work, but I always see reviews that say they taste awful.  Usually reviews of water purification systems that include “tastes awful” are attached to iodine based systems.  One example with decent reviews, however, is the Katadyn Exstream XR.  It’s iodine based, but the reviewers are either kind or just don’t mention the taste.  Most of these precombined systems don’t do anything against chemical contaminants, but they eliminate critters.

I realize this is a huge post, even for me, but it’s an important issue and there is a lot of info to sort through out there.

There is also a method I didn’t mention – bring your own water in.  That works, but it’s heavy and you still want a backup system.