Tuesday, December 8, 2015

Water Treatment - "I'll just use drops"

Yesterday I heard that sentence. "I'll just use drops" she said. This is not a good sentence when you are advising someone on gear for an extended trip. There is a lot of misconceptions about water and water treatment for the backcountry. I would like to dispel some of them now, or...

Everything you wanted to know about water treatment for the backcountry but were afraid to ask!

What are we afraid of? If you are adventuring in North America, in regard to water, you have two things to worry about. Giardia, and Cryptosporidium. Both are intestinal parasites, that give you gastrointestinal distress, which can actually be life threatening. There are many ways to take care of these two water born nasties. Lets talk about how pervasive these are later. We will also talk about viruses in your water later.

You can outright kill them, with chemicals or ultraviolet light. Or you can remove with with some form of filtration. Here is a rundown on all three methods.

Chemicals: Drop a tablet or drops into a liter of water and wait, or create a solution of some sort, drop it in a liter of water and wait. this is the chemical method, but there are different types of chemicals for this process and they have varying degrees of success.

Iodine is the most common, and the least effective. It is cheap, which is why it is so common. Simply add it to your water, wait 30 minutes and you are good to go. Sort of. It only kills giardia. Cryptosporidium has a hard shell, that Iodine can't penetrate. DO NOT USE IODINE!

Chlorine or Chlorine Dioxide. These work well. They kill both Giardia, and Crypto, and depending on which you use, it can only take 30 minutes, but depending on the brand it may take up to four hours. MSR and Aqua Mira are the brands I look to, if I choose this method. NOLS uses Aqua Mira. Great product for long trips. Also kills viruses which we will talk about later.

UV Light: UV light systems made by steripen or camelback use light to kill giardia, crypto and viruses. It is quick, 60 to 90 seconds. It is theoretically effective. I have had chemists tell me when they do the same thing in a lab they use a much longer 'dwell time'. They don't understand how these devices can work in 90 seconds. There is also the problem that the water has to be clear. If there are floaties in the water, the light can't get to the things it is trying to kill. Which means you may be pre-filtering the water so the water is clear (though this could be as simple as a bandana or a coffee filter) Let's also not forget that they require batteries and electronic devices can break.

Then there is filtration. Filtration uses some form of pressure to force water through a material. This material has to have .2 micron holes or smaller, to allow water molecules to pass through without letting giardia and crypto pass through. Add something like charcoal, or carbon to the process and you also remove odors and flavors. Historically, this pressure was created by pumping. If you have been active in the outdoors for along time you know the Katadyne Hiker and Hiker Pro, as well as the MSR Waterworks, and MiniWorks. Later MSR released the Sweetwater which was smaller and faster then the other filters i have mentioned. All of the filters I have mentioned with the exception of the Waterworks is still in production.

All of these filters utilize some form of replaceable filter cartridge, so when you are shopping, think about how fast it filters a liter of water, how much it weighs and how long the filter cartridge will work. They are generally in the range of 1000 liters or 200 gallons.

About ten years ago people started to say they hated pumping water. It was hard work, and it was slow. Various companies released gravity fed systems, where you fill a bag with water, and hang it in a tree, and gravity forces it through a filter into a receptacle. No pumping, but they tended to be bigger and harder to pack.

Then about five years ago, we saw a big change. Sawyer and MSR released Hollow Fiber technology. Here is how hollow fiber works.

I am a big fan of Sawyer filters, I used them on both the Inside passage and the AGAP PWS trip, and we had exactly zero problems. I love the versatility of the sawyer squeeze and mini. They can be hand held, used in line with a reservoir. In a water bottle like a Lifestraw. Or you can turn it into a gravity system like we did. No filters to change, just periodic cleaning. An important thing to note, Hollow fiber technology doesn't get out odors and flavors. If your water tastes like poo, after filtering with hollow fiber, it will still taste like poo - but be safe to drink. We did experience this once in Alaska. We had questionable water as our only option. We drank it with a drink mix until we found better water.

The lifestraw is incredibly popular and it is also a terribly flawed product. It can really only be used as a straw, from either the water source or a water bottle (that is now contaminated with unfiltered water). It is popular because of amazing marketing, that went viral, much like the biolite stove, something that is also amazingly flawed. The lifestraw has lifespan of 200 gallons, versus 100,000 gallons for the sawyer mini or 1,000,000 gallons for the sawyer squeeze. The lifestraw costs 4 dollars less than the sawyer mini.

There is one thing I left out of this equation. Viruses. Viruses are even smaller than Giardia and Crypto, and historically have been hard to filter. Though every year there are more options for filtering viruses, as sawyer even makes a filter that will do it. Viral level filters tend to be harder to pass water through, as you have to pass it through an even smaller hole. It is important to note that Chlorine and Chlorine Dioxide both kill viruses and can be used in conjunction with a filter if you are in a location with questionable water. When water has been treated for viruses, it is referred to as purified. Filtered water still has the potential for viral infection, Purified water doesn't.

How common are viruses in our drinking water? Not very. At least in North America. If you are backpacking or paddling in North America it is a non-issue. While we are talking about how common things are, how common are Giardia, and Crypto? Great question, and there is no definitive answer.

In the 80's a hiking club decided to take it upon themselves to find out. They sent sterile water bottles to hiking clubs in all 50 states. Asked them to fill the bottle with water from a popular hiking destination in their area and send it back. They paid to have all the water tested. They found about a third of water was contaminated. This is a very unscientific test.

This doesn't mean, you don't have to filter your water. You absolutely should. Particularly considering how small, light, fast and inexpensive filters have gotten.

The final thing I want to talk about is this. I have heard many times "this filter doesn't work, because I used it, and the next morning I had diarrhea." This isn't a water filter problem, this is a hand washing problem. After going to the bathroom the person didn't practice good hand hygiene, and then ate dinner with their hands. Yuck, but all too common.

You probably won't see effects from Giardia or Crypto for 10 days. Both have to get into your digestive tract and have time to reproduce. Giardia is the slowest, 7 to 14 days. Crypto is technically listed as 1 to 14 days, but 7 to 10 is normal.

A couple of final questions I get asked:

"What about boiling?" Boiling works great. The water just needs to come to a full rolling boil - temp of 212F or 100C - you don't need to let it boil for X minutes. But it does use up fuel, and you have to wait for it to cool.

"What about bleach in my water?" Go for it. I don't know the ratio, like 3 drops per gallon, and 30 minutes? Find a reliable source online for the ratio.

"Can I cook with untreated water?" if you will be using high heat/it will have opportunity to boil, absolutely.

"if I shower in the backcountry do I have to use treated water?" No. Just keep your mouth closed. I would however brush your teeth with treated water.

I think that should cover it.


  1. I have more than 30 years of water treatment experience and this is the best article I've seen for the layman camper. Very good advice here. I have used all these technologies and you do a great job of covering the strengths and weaknesses.

    1. Well, that is about the nicest thing I have heard in a while. Thank you.


  2. I have studied this extensively and I agree with Canoe Sailor, this is one of the best, most sensible posts I've seen on the topic.

    I didn't notice a mention of bacteria. Bacteria such as Campylobacter jejuni have been shown to be a significant risk factor in backcountry water as shown in the paper "Campylobacter enteritis from untreated water in the Rocky Mountains" and others.

    I think the incubation period for giardiasis, the time from when cysts are ingested until symptoms occur, is shorter than often quoted. Two of my most trusted sources, the CDC and the Waterborne Pathogens website agree that the incubation period is 1 to 14 days with an average of about 7 days.

    I highly recommend the latter website for scientific, up-to-date information on waterborne pathogens.

    Bleach, aka chlorine is ineffective against crypto. Chlorine dioxide is a much better disinfectant.

    Lastly, I've gathered a long list of scientific papers directly relating to backcountry water pathogens and treatment:



    1. Thanks so much Buck, I saw the CDC info, and rounded it up slightly to match other sources, I was unaware of the other link though, thank you.

      I also didn't know bleach didn't work on crypto, good info. thanks.

      I am untrained in the danger of campylobacter, I will remedy that. Thank you for all the information, and for stopping by.


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