Primer: Water Purification in the Outdoors


Clean drinking water in the wilderness is never guaranteed. No matter how pristine the lake or stream, microbes like giardia and cryptosporidium can inhabit the waters, threatening illness that might wreck a trip or affect a camper weeks after they are home.

In the woods, I use multiple water-purification products, from tablets to pumps. Product weight, speed of purification, and filtration type are criteria I assess to choose the right weapon against the bacteria, viruses and protozoa that may exist in a particular place.

katadyn tablets.jpg

Chlorine-dioxide Micropur tablets from Katadyn

Drop-and-dissolve tablets, including Potable Aqua iodine ($7, and Katadyn’s chlorine-dioxide Micropur product ($12.95,, are my most common defense. They are relatively inexpensive, light weight, and easy to use — just add a tablet into your water and let it fade away and do its stuff.

But tablets have a few limitations. You often have to wait 30 minutes or so for the chemicals to take effect. There is an aftertaste, too, especially with iodine. And for cryptosporidium, a nasty contaminant found in some areas, tablets will take four hours or more to neutralize, making them nearly unusable except for overnight application.

potable aqua.jpg

Potable Aqua iodine tablets

Much faster than tablets, pumps like the HyperFlow Microfilter from MSR ($99.95, can purify liters of water per each minute of hand-pumping action. The HyperFlow is small and weighs about 7 ounces, making it more than suitable for backpacking.

msr pump.jpg

HyperFlow Microfilter from MSR

The Platypus GravityWorks Filter ($109.95, is a neat option. It has two water reservoirs connected by a hose. Fill one side with “dirty” water and hang it up to let gravity do all the work. Water trickles from one reservoir to the other, passing through a filter for purification along the way.

Caveat: Both the MSR pump above and the GravityWorks Filter will eliminate protozoa and bacteria, but not viruses. Though rare on wilderness trips, viruses can be present around human habitation, notably in the water you may filter to drink on a trip through a developing country.


Platypus GravityWorks Filter

To expunge all biological contaminants — bacteria, protozoa, and viruses included — a product called the SteriPEN AdventurerOpti uses an ultra-violet light to neutralize suspect water. Simply dip the UV light wand into your water and let it shine for 90 seconds to “clean.”

I have used the AdventurerOpti ($89.95, on several trips, including a two-week trek in Nepal. It is easy to wield and lightweight at just 3.6 ounces. One downside: The SteriPEN does not work in cloudy liquid. You must filter murky water before zapping it with the magic UV light.

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AdventurerOpti UV-light purification product from SteriPEN

A final option, the old-fashioned trick of boiling water on a campfire is a foolproof purification plan. Boiling will kill all the bad stuff. But it is a slow process requiring a pot, an open flame, and then time to boil and, finally, wait for the water to cool before you can drink.

—Stephen Regenold is founder and editor of

Posted by Chas. Bruske - 04/21/2011 03:23 PM

So, if you choose the pen, what filtering system do you use to clarify the water?

Posted by RW Cook - 04/21/2011 03:26 PM

it’s worth pointing out that iodine tablets are not effective on cryptosporidium, though chlorine dioxide is.

Posted by Thirsty - 04/21/2011 04:33 PM

My vote: Gravity fiters rule!

Posted by Stephen Regenold - 04/21/2011 04:37 PM

RE “if you choose the pen, what filtering system do you use to clarify the water?”. . . answer is you can use anything. A piece of cloth even will do. Just need to get rid of the sediment and the murk.

Posted by Bernie - 04/21/2011 07:09 PM

A less popular, but very efficient, option is the MSR MIOX. It has a small reservoir of salt and a battery powered electrolyzer that creates mixed oxidants in a small reservoir of water. Pour this activated water in your bottle and everything gets killed. It has a much longer battery life than the SteriPen. It’s as light as the lightest reusable devices. The main drawback is that learning the right technique to dissolve the salt in the water reservoir is tricky.

Posted by TJM - 04/21/2011 09:38 PM

I am stunned you didn’t mention the FIRST NEED filter/purifier.

Posted by Erik - 04/22/2011 01:12 AM

I’ve used Aqua Mira on every trip for 5 years now after getting introduced to it on a NOLS course. Little to no taste beyond what the water already has. 20 minutes from filling the bottle to drinking w/o having to stop to pump. No batteries and you can take it into frozen locations (unlike a filter system).

Posted by David - 04/22/2011 11:25 PM

It’s also worth mentioning that the Katadyn Pocket is a solid option, with a field-cleanable ceramic filter that lasts for 13,000 gallons. That’s a lot of water!

Posted by Luke - 04/23/2011 12:17 AM

I also think it is worth mentioning the sawyer drip filter. If weighs just about nothing and is 0.02 microns. I am waiting for them to come in stock, cant find them anywhere. I currently have an MSR sweetwater, which is great but a bit heavy and it would be nice to have a drip, set and forget.

Posted by FedEx - 04/23/2011 10:04 AM

It’s hard to beat Chlorine-dioxide tablets for the ultralight hiker/backpacker. Virtually weightless. And most of us aren’t likely to need to worry much about viruses. (Life is full of small risks everywhere). When planning to refill I usually save a swallow or two to wet my whistle before refilling – its more psychological than anything, but it helps stave off that “panic” of being parched without water. (I carry gum for the same reason-and that really works when stretching my water supply, though obviously its a temporary stalling measure.) Then I’ll fill an extra bottle and resume hiking. 30 minutes wait time goes by surprisingly quickly and then I drink that extra water to “camel up” and not carry the extra weight all day. If hiking somewhere where I was particularly concerned about viruses I’d probably use my steripen. But otherwise even the added 3.3 ounces is no real advantage to me. Most filter users should remember that for all that weight they still aren’t treating for viruses – so why carry the weight? Works for me.

Posted by KO - 04/23/2011 03:41 PM

In the wilderness, using a water-purification product is close to being hysteric. I’ve never used it and it has never caused me any problems. By drinking/fetching water from a fresh looking, moving stream you’ll avoid most risks.

I cannot think of anything that tastes better than water straight from the stream!

Posted by jpea - 04/24/2011 10:36 PM

until you’re on day 4 of some race only to find that your gut has been compromised because of some bacteria or parasite and you’re shit out of luck (literally) :)

Posted by Brett - 05/18/2011 07:27 PM

KO – Just because you have done it, and continue to do it doesn’t mean it is safe. There is great debate as to how much our water is contaminated, but there is no debate that things like Giardia, and cryptosporidium are out there. There is zero correlation between ‘fresh looking, moving stream’ and cleanliness. While I do agree that people tend to be paranoid about a lot of things. this is one that I think makes sense to cover your bases.

jpea – Just an FYI, in general intestinal issues from Giardia and Crypto take a week to ten days to show effects.

Posted by Jordan Karp - 06/14/2011 11:47 AM

These are great. Nobody likes bringing bottled water with them in the wild. I’ll definitely check out the iodine for my upcoming camping trip!

Posted by Tom Varoz - 07/02/2011 08:23 AM

I am the owner of 7summitsgear. I always take with me some type of water purification. About a month back 6 of us went off to do Bluejohn’s Canyon in Southern Utah. We did 3 slots in one day, around 16 miles of hiking. Well we thought there was going to be water but not a drop to be found till the end of the last slot we found a small pool of stagnant water. I would have rather tried getting water from a bathroom stall at a truck stop is what crossed my mind while we filled up one of the bags with the katadyn hiker pro. After only getting about 100 oz of water before it clogged up with slim and goo we headed out with 5 hours of hiking left to go. We ran out of water with about 3 hours left. No wanted to drink the bluejohns water. We all finally broke down and had a sip of Bluejohn water and that 100 oz got all 6 of us back safely to are camp. A month later and we are all healthy and no Giardia, and looking to to do Neon canyon in a few more weeks.

Posted by Vladislav Vasilkevitch - 07/21/2012 05:25 AM

This is amazing technology. All you need is to carry it along whenever we go out and can assure a great pure quality water anytime and at anyplace.

Posted by Håken Hveem - 08/25/2012 03:37 PM

What about lifestraw ?

Posted by thatsfunny - 02/13/2013 09:26 AM

Said KO- “I cannot think of anything that tastes better than water straight from the stream!”
lol…and you will get ko-ed

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