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Wilderness Safety and the TRUTH about Wilderness Survival: Treating "wild water."

My opinion on this topic is in accord with the C.D.C. and the E.P.A., so to keep the record straight: we are generally talking about four types of pathogens; Specifically 1) Giardia, 2) Crypto’ (Cryptosporidium), and generally 3) Bacteria, and 4) Viruses. In all cases, they can get into wild water through human and animal waste. Solids like salts or minerals require specialized water purifiers (if the water is treatable at all). This post also deals with three treatment options: 1) Boiling, 2) Filtering, and 3) Chemicals (i.e. Potable Aqua, Aquamira, etc.)

Giardia and Crypto’, in first-world countries like the U.S., are normally the only things we have to be concerned with. Most good 1-micron filters will be sufficient for these. The symptoms for both present in about a week, and while those symptoms are usually mild, they can be severe for some people. If you’re in the backcountry, and you know you’re going home soon, then it’s really not a big deal. If it’s a problem later, just get a prescription and take some pills. However, people usually DON’T know when they’re going to find themselves in a survival ordeal, so if you’re on day 2 of a 7-day outing after drinking untreated water, THEN find yourself in a survival ordeal, your situation just became that much more complicated with probable dehydration. Yes, any decision to opt for diarrhea instead of dehydration is a calculated risk.

Bacteria presents the next level of consideration with wild water. These are smaller than Giardia or Crypto’, so for this you need a better .03-micron filter (read labels!). These are things like Escherichia coli (or “E. coli”), Salmonella, etc. Symptoms from these can present anywhere from a few days to a few weeks, so again, your risk depends on whether you go home on time, but the consequences are much more risky!

Viruses are the most serious consideration with drinking untreated wild water, most often in third-world countries, they are about .02 to 1 micron in width, and 1 to 10 microns in length, so they’re hardest to filter out. These are things like hepatitis A, rotavirus, enterovirus, norovirus, etc. Symptoms from these can present anywhere from 1 day to a few weeks and have the most serious consequences. So again, ultimately the level of risk depends on going home on time.


Boiling is the “Gold standard” of wild water treatment! Boiling is the ONLY highly effective treatment that WILL make wild water safe!! As long as the water is clear, or at least slightly cloudy (Not muddy or contain a lot of silt), BOILING is the only, single, method that WILL guarantee safe water. Otherwise, always try to arrive at the best possible water before filtering/treating by screening-out particulates (i.e. with a head net or t-shirt, etc.) Water from a “waterfall”, a “fast moving” river, or water that is cold, are NOT indications of clean, safe water. Only BOILING will work, clear? Most knowledgeable people will say it’s only necessary to bring water just to the point of boiling, (which is true). Still, I recommend boiling for 1 minute, 3 minutes if above 6500 feet or if the water has slight particulates, etc.

If boiling is not an option, using a 1-micron filter for Giardia and Crypto’ is fine. For bacteria, a .03-micron filter AND chemical treatment (usually iodine or chlorine) will make it just as safe as boiling. For viruses, while using a .03-micron filter helps a little, with chemical treatment (although not as effective as boiling), should make it reasonably safe. However for viruses, I would recommend using a water purifier (if you have one) with a chemical treatment to be sure, but water filters by themselves are NOT effective against viruses at all.

What if you have no fire, AND no filter? With Crypto’, iodine and chlorine are NOT effective at all, and chlorine dioxide will only give low/minimal effectiveness. With Giardia, iodine and chlorine give low/minimal effectiveness while chlorine dioxide gives good protection. With bacteria and viruses, iodine, chlorine and chlorine dioxide all give good/acceptable protection (but they’re much better with filtration!).

With potassium permanganate, just a few crystals can treat a quart/liter of water (about 0.01% solution or 1 gram per liter, 3 - 4 crystals), just enough to make the water a light pink (That’s LIGHT pink, not “Pink”!), with contact time from 2 to 24 hours. But it’s interesting to note that it’s not as effective as chlorine dioxide or as safe.

UV light (or “solarizing”, done by putting the water in a clear glass or plastic P.E.T. bottle) is also effective, but it depends on following the standardized recommendations and good pre-screening practices. Particulates in the water (and temperature and altitude) always inhibit treatment effectiveness, so screening-out silt, debris, etc. before filtering is always recommended.


How does chlorine dioxide differ from sodium hypochlorite? (common household bleach). Any topic involving science/chemistry can get rather scientific, so I’ll try to keep it simple. The difference between chlorine and chlorine dioxide is HUGE! The only thing they have in common is the word "chlorine" in their name and that they're both water soluble, THAT's where the similarity ends! The chemical makeup, the way they react, their strength, etc. are ALL different.

Chlorine Dioxide is a more powerful oxidant. It undergoes 5 changes in its oxidative nature, Chlorine is only capable of 1, so Chlorine Dioxide is 2.6 times more powerful. Chlorine Dioxide acts only by oxidation, Chlorine will combine to produce harmful Chlorinated byproducts (e.g. chlorinated phenols, THM's, Dioxins etc.), many of these byproducts are recognized carcinogens. The properties of Chlorine are very pH dependent; Chlorine Dioxide is effective at all pH levels below 12. Chlorine has been found to be ineffective against complex organisms (e.g. cysts and protozoa, both giardia and crypto' are protozoa), but Chlorine Dioxide has been found to be effective against a wide range of organisms. Chlorine cannot be used at high temperatures (104F/40C) because it tends to dissociate evolving Chlorine Gas. Chlorine Dioxide does not dissociate as readily at elevated temperatures. Chlorine does not remove Biofilm. Chlorine Dioxide Does. Basically, Chlorine Dioxide is better and safer.


There are two common methods for water purification tablets: Iodine and chlorine. Iodine is the arguably more effective method, but it leaves an iodine taste. It is suggested the taste may determine how much or how little one drinks. So, how do you deal with it? Some products like Potable Aqua include a second bottle with tablets you can add to remove the taste, OR, simply adding vitamin C (i.e. Tang), or adding a pinch of salt per quart, adding flavorings (e.g., lemonade mix, etc.) should do it or you can just pour it back and forth between containers (again, AFTER it has been adequately treated).

The other option is chlorine. Chlorine should be used for persons with iodine allergies or restrictions like persons with thyroid problems, are on lithium, are allergic to shellfish (they may also be allergic to iodine), women over fifty and pregnant women should consult their physician prior to using iodine for purification. Be aware that iodine is light sensitive and must always be stored in a dark bottle, once opened, it may need to be used within a certain time.


With more medical uses of iodine (especially as a radio contrast media), more instances of reactions have been reported in recent years. It is a commonly held belief among radiologists and other medical professionals that there's a specific cross-reactivity between iodinated radiographic contrast material and other iodine-rich substances.

Iodine is a common element found in, among other places, the human body so reactions to iodine are extremely rare, but they do happen. "Iodine allergy" is used as a collective term for adverse reactions, and though iodine is not generally considered an allergen, some people who are hypersensitive may be considered to have an iodine "allergy." In a few cases, iodine has even been responsible for patient deaths.

Evidence exists of a nonspecific cross-reactivity between contrast material sensitivity and allergy to seafood (as well as other foods). Patients reporting iodine or seafood allergy should be questioned as to the exact nature and severity of the reaction. If possible, seafood allergy should be distinguished from other causes of seafood intolerance. The presence of a seafood allergy places the patient at a threefold risk of an adverse reaction to iodine contrast material. As with any other allergy, the nature and severity of the reaction should be considered when choosing the type of contrast material and when determining the need for a premedication regimen.

Finally, iodine and chlorine will NOT work on toxic water (water that has dissolved chemicals or solids like salt). In that case, it MAY be safe/safer to add the use of absorbent filters (i.e. with charcoal), but the BEST advice is to simply NOT use toxic water!

Potable Aqua, for example (both the iodine and chlorine versions), are effective against viruses, bacteria, and cysts (such as giardia and cryptosporidium). But while the iodine version can work in as little as 30 minutes, the chlorine version may take a 4-hour treatment. ALL chemical treatment is effective, HOWEVER, you need to use clear or virtually clear water, AND it can't be too cold or you may need to increase the treatment time.

The effectiveness of all chemical treatment of water is related to the temperature, pH level, and clarity of the water. Cloudy water often requires higher concentrations of chemical to disinfect. If the water is cloudy, strain it, add the tablets and swish it around. Splash some water with the chemical onto the lid and the threads of the water bottle so all water areas are treated. The water should sit for at least 30 minutes. The colder the water, the less effective the chemical, it works best if the water is over 68F/21C, if the water temperature is below 40F/4C, double the treatment time before drinking.

I always suggest you have at least TWO options for water, fire and shelter. Here, tablets are one, the other is a filter like Sawyer (it has the distinction of being able to be used almost perpetually by simply backwashing it!). But the best method is still boiling, some say you don't actually have to "boil" water to make it safe, that by the time water actually comes to a boil it is already safe, but I like to see bubbles for my own peace of mind!

19 Replies

I was pointing you to evidence in the form of the PET UV transmission spectrum.  The spectrum shows that PET strongly absorbs light below 300nm, with some PET variants having an even higher UV cutoff.  SODIS requires UV light shorter than 300nm.  That means SODIS will be ineffective using PET containers.  

Instead you need a container that will not filter out (absorb) the wavelengths necessary for pyrimidine dimer formation.


no association with milk implied.




Now that I have a few minutes… Although I appreciate your interest (and attempt to engage on my level), your argument, quite frankly, falls short. Setting aside, for just a moment, the fact that SODIS (Solar Water Disinfection) has been around since at least the mid-eighties (I believe), and that the CDC, the NCBI, the WHO and other international organizations are all very well aware of the use of PET (polyethylene terephthalate) plastic bottles for SODIS use, and of course the BILLIONS of people all over the world who have benefited from precisely that, “Mooniac” has an opposing opinion, shall we?

Firstly, while you are very emphatic about “… no association with milk implied…”, you’re also very nonspecific, but presuming you’re talking about the figure at the top of the page you cited (at, I can only guess you didn’t actually READ the very article you cited starting with the title, which is, “Protective Influence of Several Packaging Materials on Light Oxidation of Milk”, 2005, from the Journal of DAIRY Science (which you would have easily found if only you had clicked the “view publication” button. HELPFUL HINT: You may want research that is on point to support your arguments!

Alternatively, you may want to re-start your research with a ‘quick’ look at an article called “Solar Disinfection of Viruses in Polyethylene Terephthalate Bottles”, 2015, from a journal called Applied and Environmental Microbiology (at, which I found with just a quick check. An even MORE on point article called “A Pilot Study of Solar Water Disinfection in the Wilderness Setting”, 2014, from a journal called Wilderness & Environmental Medicine (at may also be of interest, if your interest is sincere.

On the other hand, you may simply want to read (or RE-read) my earlier post on SODIS in which I wrote, “Pathogenic microorganisms are vulnerable to two effects of sunlight: radiation in the spectrum of UV-A light (wavelength 320-400nm) and heat (increased water temperature). A synergy of these two effects occurs, as their combined effect is much greater than the sum of the single effects. This means the mortality of the microorganisms increases when they are exposed to both temperature and UV-A light at the same time.”

You apparently disagreed stating, “… PET strongly absorbs light below 300nm…”, clearly this is a NON-issue since, as I stated, UV-A has a wavelength of 320-400nm! (not that you mentioned which TYPE of UV light you were referring to, perhaps UV-B?) I will say this, the ability of SODIS to kill viruses is less certain than bacteria, but that’s nothing new if you read my initial post since I made it clear viruses are harder to kill than bacteria. On the other hand, HERE, in North America (specifically the U.S. as in other first-world countries), we don’t really have viral issues with our water. In fact, and to restate, our backcountry “wild water” is actually fairly clean! Sure, there is the POSSIBILITY of giardia or crypto’, but except for relatively few people, they present essentially non-issues making SODIS a very valid and viable solution as an emergency water treatment option, particularly in emergency/survival situations. Questions?


I’m watching this show called Alone where 10 people are dropped into the wilderness and I’m watching this man walk the course of the river talking about I need water! I’m like what do you mean you have a whole river. He said he’s not worried about making a fire, he needs to find water while walking next to a river. WTF. So i had to look around and see if I am tripping. Can’t you just boil it I thought to my self? So yeah thanks for the great article. 


@@Citygirl123 LOL!

Ah yes, on The History Channel, I know it (and they know ME... or at least they know my trail name / online handle). I almost always know who has a chance and who doesn't (near the beginning), andwho will tap-out next.

I don't know what his issue was, do you have the production number? (season and episode).



LOL. Well it was season 1. I don’t know production number or anything. As I continued to watch I realized maybe it was because he was on the ocean and it was salt water. But even still they had pots and tarp and it pretty much rained 85% of the time. 



AH, yes, I predicted Allen Kay would win before the first episode was over! The rest were fakes, frauds and pretenders!

I seem to recall one guy who poured brackish water through spagna moss, thinking THAT would make it potable. DORK!!

Another (young-is) guy who was trying to collect rain water with his tarp in the hole of a log.

Any of those ring a bell? And yes, part of the game is they can bring a limited amount of gear.



I have "Alone" recorded (of course), but I don't feel like going through it to find your reference. Instead, I'll just do a few posts for you, one on seawater and one on sphagnum moss.

And yes, he could have caught rainwater with the tarp and kept it in his pot. If he had a tube, he may have been able to make a water still.


Really? No discussion of Steripens and UV light purification? This must be a surprise to NYC that only uses UV for water purification


LOL, okay. I did cover solarization/SODIS, but okay.

They may have come up with a better version of the Steripen, but I recall seeing reviews that complained it tended to fall apart. Also, it uses batteries, so there's THAT issue. But otherwise, it works. However, as with solarizing/SODIS, the water MUST have low turbidity! (cloudiness). If there are any particulates, they really SHOULD be screened/filtered out. Otherwise the UV light can't do its job.

Most cities that use chlorine to treat their water have, or are, switching to chlorine dioxide. However, most bacteria only take about 10 seconds to kill with UV light, provided the light source is within about 6 inches. NY has the LARGEST UV (Ultraviolet Germicidal Irradiation to be exact) treatment system, San Francisco also has a massive UV system, so it could be a model for other cities/countries in the future. But as I said, UV works best IF the water is clear.



Along with UV treatment, "ozonaton" (treating with ozone gas) is another option that has received a lot of research. You can buy ozone generators, but I remember seeing a D.I.Y. approach.