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Backcountry Water Treatment Part 4: Methods for Making Water Safe

December 8, 2008

All drinking and cooking water should be treated, regardless of how clear and clean it looks.
(photo: A. MacLeay)

Short of transporting all your water from civilization and municipal water supplies, there are three general methods for treating your water for drinking and cooking, and two more recent additions:




Although sterilization by heating is referred to as “boiling,” it is not necessary to actually bring water to a full rolling boil or to boil for 5 to 10 minutes, as is often stated. Raising the temperature of water to 155°F (70°C) is sufficient to kill most biota encountered by backpackers. This is also the temperature required for pasteurizing milk.

The temperature at which water boils decreases with altitude. However, the boiling temperature is higher than 155°F (70°C) at all altitudes that you would camp at (even on Mt. Everest with a boiling point of approximately 167°F / 75°C). Since few people carry a thermometer capable of measuring water temperature on a backpack, the most practical approach is to heat water until it starts bubbling.

Note: the Environmental Protection Agency (EPA) and the Centers for Disease Control and Prevention (CDC) both recommend boiling water for one minute. If you are above 6,562 feet (2,000 meters), the recommended boiling time increases to three minutes.

Advantages of Boiling:

  • Boiling kills most microorganisms.

    Raising your water’s temperature to boiling is an easy way to treat it for cooking and drinking.
    (photo: D. MacLeay)
  • Boiling is the most practical and simplest approach to sterilizing water for meals, since you have to raise the water to boiling for most backpacking foods anyway.
  • In winter, when you often must melt snow or ice, you usually will raise the water to boiling, as well.

Disadvantages of Boiling:

  • Boiling does not remove silt, glacial flour, or volcanic ash, though it will sometimes reduce turbidity from plant material in the water.
  • Boiling does not remove chemical contamination, though it can drive off some of the sulfur compounds.
  • Boiling requires burning fuel. Since you generally will be carrying your stove fuel with you, this means carrying extra weight.




Filters depend primarily on forcing water through a medium with tiny holes to physically remove microbes and matter. Anything larger than the hole size is blocked, so a filter’s effectiveness depends on its “pore” size. Most filters available for backpackers remove all parasites and bacteria, plus some viruses. They remove most of the particles that cause turbidity. However, few filters for backpackers remove the smallest viruses.

The Katadyn Exstream XR bottle purifier uses a straw.

Filters sold as “purifiers” (First Need, for example) use a chemical purifier to kill viruses, usually an iodine resin. Purifiers must prove inactivation of all three biological contaminants (protozoa, bacteria, and viruses) to meet the EPA Guide Standard for Testing Microbiological Purifiers.

There are filters, known as “reverse-osmosis filters,” available for desalination. However, their size makes them impractical for backpacking, though usable for ocean-going sailboats and other larger vessels.

Backpacking filters may work via a pump (a manual pump forces the water through the filter element), “straw” (your suction pulls the water through the filter), or gravity. Ease of use and the speed of filtering are considerations when selecting a filter.

 A pump filter, the MSR Miniworks EX.

Advantages of Filtering:

  • Most filters are effective against bacteria and parasites.
  • Some filters remove larger viruses.
  • Filters remove some turbidity.
  • Filters are usually convenient and fast.

Disadvantages of Filtering:

  • In areas where viral contamination is present (Third World countries, for example), additional purification by boiling or chemical treatment is still required.
  • Few filters remove chemical contamination; those that do remove only a limited range of chemical contaminants (usually with an activated carbon element).

    A gravity-fed filter, the Katadyn Base Camp.
  • Fine particles like silt, glacial flour, and volcanic ash will clog any filter, requiring field maintenance (backflushing, cleaning with a brush made for the purpose, or replacement of the filter element). Many filters have pre-filters available to reduce the amount of material that will cause clogging – use them. Settling can also help.
  • If the filter freezes with even a tiny amount of water in the element, the element can crack, rendering the filter useless.
  • The moving parts of pump filters can break, rendering the pump useless.
  • Pumping can be tiring.

Proper Use of Filters:

  • Always store the intake hose separately from the rest of the pump.
  • Use the covers for the inlet and outlet to prevent contaminating the filter element on the outlet side.
  • Protect the filter from freezing.
  • Clean the filter regularly according to the manufacturer’s specifications.
  • Use a bucket, pan, fold-up basin, or other container as the source of the water for the pump, rather than pumping directly out of the stream or lake (at least 100 feet from the water source). This is both for avoiding the watering area for local animals and to reduce the amount of suspended material entering the screen on the pickup and into the pre-filter.
  • If possible, let water stand overnight to allow suspended material to settle out.


Chemical Treatment: Iodine and Chlorine


The chemical treatment approach uses one of two halogens (chlorine or iodine) to kill biota. This is the method most used by municipal water supplies around the world. The backpacker’s approach is to use a small amount of the halogen, rather than the massive treatment plant used by your local water company. The halogen may be applied in one of two forms – a tablet that is dissolved in the water to be treated or in a solution of the halogen in water. Both iodine and chlorine are very effective against the most common pathogens, but they require sufficient time to act. Like all chemical reactions, the time required increases as the temperature decreases.


Potable Aqua tablets use iodine.

Iodine is most commonly used in the form of tablets, such as Potable Aqua water purification tablets. One or two tablets are added to each liter of water, with the time required being about 30 minutes for “room temperature” water (always follow the manufacturer’s instructions).

Alternatively, a small amount of a saturated solution made from iodine crystals is added to the water to be treated. The most common form of this treatment is Polar Pure. With Polar Pure, the crystals are in a bottle that has a “trap” in the mouth of the bottle to ensure that only the saturated solution of iodine in water and no crystals gets into your drinking water. One capful of the solution is measured out and poured into your one-liter water bottle. Then the Polar Pure bottle is refilled to allow a saturated solution to be formed for the next treatment.

Advantages of Iodine

  • Chemical treatments, like iodine, are very effective against most common pathogens.
  • Iodine is faster than chlorine, approximately 30 minutes versus up to 4 hours.

Disadvantages of Iodine

  • Does not kill the parasite cryptosporidium.
  • Chemical treatments do not remove chemical contaminants or turbidity.
  • Requires time to work (approximately 30 minutes); Temperatures below 70°F (20°C) and turbid water require increasingly longer times.
  • Some people react badly to iodine, particularly people with thyroid problems.
  • The medical community recommends that continuous usage of iodine-treated water last no more than 3 to 4 weeks.
  • Many people find the iodine taste objectionable (mixing in some citric acid in the form of lemon juice or tablets will kill the taste, but be sure to wait until sterilization has had plenty of time to take place).


Chlorine is most commonly used in the form of chlorine dioxide tablets or drops, such as in Aquamira, Katadyn Micropur, and Potable Aqua Chlorine Dioxide. It can also be used in the form of laundry bleach (be sure it is pure hypochlorous acid and not mixed with perfumes or other chemicals) or a solution generated from rock salt, such as done by MSR’s MIOX purifier.

While chlorine will kill most bacteria and parasites in a few minutes, a much longer time is required to kill the cysts of giardia and cryptosporidium, as well as many viruses. Typically 4 hours or more is the recommended time for room temperature water (70°F/20°C), with an increase for colder water, such as from mountain streams (always follow the manufacturer’s instructions).

Chlorine can be used indefinitely, unlike iodine. It’s what you drink in most city water systems. On the other hand, one of the joys of fresh stream water is its clean taste with no chemical smell or taste. The much longer time required for chlorine treatment is also a problem. The solution is to carry two water bottles, which are alternately refilled and the chlorine added at each water source. That way, you have a full bottle available when you empty the other.

Chemical treatments do not remove chemical contamination, and in fact can react with certain agricultural runoff. This is unlikely to be a significant problem for the backcountry traveler, however. Chemical treatment also does not remove turbidity. Turbid water requires longer treatment times or an increased amount of the halogen.

Advantages of Chlorine:

  • Chemical treatments are very effective against most common pathogens, and chlorine kills most bacteria and parasites in minutes.
  • Chlorine can be used indefinitely.

Disadvantages of Chlorine:

  • Chemical treatments do not remove chemical contaminants or turbidity.
  • Requires time to work, up to 4 hours, for full treatment; Temperatures below 70°F (20°C) and turbid water require increasingly longer times.


Ultraviolet Radiation

The SteriPen is one fast, convenient method of treating drinking water. (photo: A. MacLeay)


A recent addition to the quiver of techniques for purifying water in the field is ultraviolet (UV) radiation. The most widely available device for doing this is the SteriPen. This is a battery-operated device that is stirred in the water (preferably a one-liter water bottle with a wide mouth) for a short period of time (couple of minutes).

To prepare for purification, fill a bottle with water, press a button on the SteriPen according to the directions (single push for one liter), then insert the pen into the water. When the contacts on the side of the pen are immersed, the light will light up. Stir the water until the light extinguishes, and the water is sterilized. The UV radiation is extremely effective against biological contaminants.

However, like the other treatments mentioned above, UV radiation does not remove chemical contaminants or turbidity. The water should be fairly clear (it need not be crystal clear), so the water should be allowed to settle or a filter used to remove most of the sediment (a coffee filter is sufficient, according to the last word I had from the SteriPen people). If the water appears slightly milky from glacial flour or volcanic ash, you may want to run a second treatment. We used this approach on Kilimanjaro with the water taken from streams on the mountain.

The Adventurer, one of several models from SteriPen.

A disadvantage of the SteriPen is that it requires batteries. However, one of the optional packages includes a carrying case with a solar charger in the lid. This requires 8 to 10 hours to recharge a pair of batteries. Since a charge will suffice for 10 liters or so of water (a couple day’s worth), this is adequate. You can carry two or three sets of the batteries as backups, although the batteries (both primary and rechargeable) are lithium-based, hence subject to the TSA restrictions on carrying no more than two spare batteries in your carry-on baggage and none in your checked baggage.

Advantages of UV Radiation:

  • Effective against biological contaminants—parasites, bacteria, and viruses.
  • Fast and convenient.

Disadvantages of UV Radiation:

  • Does not remove chemical contamination nor reduce turbidity.
  • Water should be fairly clear, though it does not have to be perfectly clear.
  • Requires batteries, but a solar charger is available.


PUR Water Treatment Kit

Open the PUR packet.


PUR, a Swiss division of Proctor and Gamble, developed a water treatment kit for use in Third World countries a couple of years ago. They have now made the PUR Clean Drinking Water Kit available in North America. This kit will purify water, removing biological and many chemical contaminants, along with suspended particulates.

The complete kit includes two 10-liter containers (one for the untreated water to be treated, the other for the treated water to be decanted into), a stirring tool, a cotton cloth filter to remove the flocculus with the trapped contaminants, packets of the treatment chemical, and a packet opening tool. The first container is filled with the water to be treated. The premeasured chemical packet, containing iron sulphate and calcium hypochlorite, is poured into the water and the stirring tool is used to stir the water to mix the chemical thoroughly. The container is then closed and let stand for 10 minutes.

Stir with the tool.

The iron sulphate forms a flocculus (similar in appearance to fluffy cotton), which settles to the bottom, carrying most of the biological contaminants, silt and other suspended particulates, and most chemical contaminants (including heavy metal compounds) to the bottom. After 10 minutes, the water is carefully decanted through the cloth filter into the second container, which is allowed to sit for an additional 10 minutes, during which the remaining pathogens (viruses) are killed by the calcium hypochlorite acting as the purifying agent. At this point the water is pure enough to pass international standards for drinking water.

The two major problems with the PUR kit are that it is currently somewhat difficult to obtain, and that the packets are pre-measured for 10 liters. You cannot use a partial packet for a smaller amount of water (the powder does not necessarily have the components uniformly mixed throughout the packet, so you must empty the complete packet into the water). While this is ok for a group (or, in Third World communities, for a family group), this is inconvenient for the individual backpacker or a small group of backpackers. However, the cost is very small, less than the cost per liter of most of the other methods described.

The resulting flocculus.

The big advantage is that this is the only method available for water contaminated heavily with suspended particulates, many chemical contaminants, and virtually all biological contaminants. It would work well for larger backcountry groups, as well as in case of a natural or man-made disaster that interrupts municipal water supplies. It will not desalinate water.


Advantages of PUR Clean Drinking Water Kit:

  • Removes biological, particulate, and some chemical contamination.
  • Particularly good for Third World and highly contaminated water sources, and during natural or man-made disasters.

    Decant. (photos: B. Straka)
  • Inexpensive.
  • Simple procedure.
  • Treats 10 liters at a time, so is best for large groups.


Disadvantages of PUR Clean Drinking Water Kit:

  • Treats 10 liters at a time—no smaller, no larger—so inconvenient for most backpackers.
  • Takes 20 minutes total time for treatment.


Chart: Which Treatment Methods Remove What


Bacteria Viruses



Yes Yes Yes No No
Filters Yes Yes

Remove some larger viruses, not smallest

A few remove a limited range of chemical contaminants Removes some turbidity
Purifiers Yes Yes Yes No No
Chemical: Iodine
Not cryptosporidium Yes Yes No No
Chemical: Chlorine
Yes Yes  Yes No No
UV Radiation (SteriPen) Yes Yes Yes No No
PUR Water Treatment Kit  Yes Yes Yes Some Yes


The information above is for general interest only. Always consult each manufacturer's specific product information for effectiveness of your treatment method against specific pathogens and contaminants.


The Bottom Line


As noted previously in “Part 3: What is in Backcountry Water,” the strong evidence is that for backcountry travelers in the United States and Canada, the major source of digestive tract illness is not waterborne pathogens or other contamination, but poor sanitation. The best prevention is paying diligent attention to simple sanitation measures:

  1. Wash your hands frequently, particularly after relieving yourself. Use soap and water and/or Purell or another alcohol-based purifier.
  2. Wash and sterilize your hands before eating, particularly finger foods (sandwiches, bars, trail mix, etc.)
  3. All individuals preparing or serving food for the group must wash and sterilize their hands, and should consider using gloves of the type now mandated for restaurant workers.
  4. All dishes and utensils should be washed before meal preparation and serving. Sterilizing by dunking in boiling water is one of the easiest and quickest ways to assure sterile utensils.

It is all too easy to be careless and neglect simple sanitation while hiking, backpacking, and climbing. But, by treating your backcountry water, staying hydrated, and practicing proper hygiene, you'll help ensure that you, and everyone in your group, has a great trip and will be back on the trail again soon.


 Read “Backcountry Water Treatment Part 1: Proper Hydration” »

 Read Water Treatment and Storage Reviews »



I work for Katadyn as their northern rockies representative. I have done a lot of research into what is in backcountry water and how to make it safe.

Unfortunately there are a few major errors in your water articles and a lot of information that is either left out or glossed over.

I will address the errors.

1. Iodine does not kill Cryptosporidum. Cryptosporidium is a protozoa that first hit the news in 1993 when over 400,000 people in Milwaukee caught it. Symptoms are similar to Giardia and it is just as common. It had simply not been researched much until the Milwaukee outbreak made the news. A 1992 study of U.S. rivers and lakes fouund 97% contained Giardia, Cryptosporidium, or both.

2. Boiling time. Both the Environmental Protective Agency (EPA) and the Center for Disease Control (CDC) recommend boiling water for one minute unless you are above 6,700 Ft., then the recommend goes to three minutes. I'll take their advice-but boiling water for all your needs in the backcountry is a real pain.

3. There are now more popular and easy to use forms of Chlorine on the market than noted in the article. Tablets that produce Chlorine Dioxide are marketed under 3 brand names. Micropur (Katadyn), Potable Aqua Chlorine Dioxide, and Aqua Mira Chlorine Dioxide. They will kill all micro-organisms in any kind of water, but take 4 hours to kill Crytosporidium in cold dirty water.

In Asia and South America, where killer viruses can be present I microfilter first to remove hard to kill protozoa (and also bacteria and turbidity), then I add Micropur tablets. EPA required testing indicates that Micropur will kill all virus within 15 minutes. I just returned from a 16 day Nepal trek where we used this technique and everyone's intestines stayed happy.

My recomendations for North America are a good quality pump microfilter, with Chlorine Dioxide tablets for backup. In 20 years of using pump filters on many, many multiday trips I've only ever been mad at one. I've never seen one irrepairably clog, break, or otherwise fail.

Thanks, Riverridgeray.

Welcome to Trailspace, Riverridgeray, and thanks for the feedback.

I've edited the article to reflect your suggestions and clarifications.

You're right that we had an error of omission and should have stated that idodine doesn't kill crypto. I also expanded our mention of the chlorine dioxide products available, as well as the CDC and EPA's boiling recommendations.

Hopefully I've addressed all issues of confusion. Thanks again

Alicia: Thank you for so quickly making those changes in the article. I realize I did not leave a comment in the "What's in backcountry water comments" but I think more information on Cryptosporidium is needed there. Two years ago I put my college science degree to work, did a bunch of research, and knocked out a 12 page, hopelessly technical paper on "What's in the Water Now." I will email it to for your perusal and or use.

Here is a link to the article on line. It got butchered a little in the posting, since they couldn't handle footnotes. thanks, riverridgeray

Riverridgeray -
I had not responded before now because I was out in the backcountry in snow for a week, then only had access to the web away from my reference materials. Since I returned home, I have cross-checked my article with several professionals in the field (we here in the SFBay area are blessed with having a number of active wilderness medicine research people, including authors of the several of what are considered to be the authoritative compendiums on the subject). Although I have training and certification in wilderness medicine, I am not myself an MD (my doctorate is in another field). I will be posting a detailed response, hopefully this week, with references to the literature.

Briefly, though, keep in mind (as posted earlier in the discussion of one of the other segments), the article was not intended as an exhaustive scholarly review of the field, but rather as a brief summary of the salient points of practical use for the backpacker and climber. It was not intended to cover all possible environments and disaster scenarios, but rather the wilderness situations encountered by most of the readers of Trailspace. There are some omissions and oversimplifications that were made in the interests of conserving space (originally, the intent was a single article, but Alicia wisely split it into 4 more readily readable sections). I will be doing a bit of editing to clarify several points.

I will note that, according to 2 of my acquaintances who are recognized wilderness medicine experts, there are several misleading or erroneous items in your post, and in the "ezine" article you link to. Without going into detail at this point, here are a couple -

1. While it is true that giardia and crypto are resistant to halogens (both chlorine and iodine), especially in the oocyst form, it is not true that "iodine does not kill" crypto. As I noted, the effectiveness is dependent on temperature and turbidity. Given sufficient time and temperatures of 20-30C, crypto cysts are killed (65 to 80% inactivation after 3 hours, 3log inactivation after an additional 4 hours with 2 iodine tablets in "general case" water). Note that the Milwaukee incident involved a failure of the municipal filtration system, and in a city using chlorine dioxide, not a wilderness situation.

2. The boil time recommendations from EPA and CDC are for sterilization of the water, not purification, and are primarily driven by the lack of data for Hep A. Sterilization means killing all the organisms. There are bacterial cysts that do not cause problems in humans that can withstand boiling water, but most biota that cause harm are inactivated at pasteurization temperatures of 155F (including giardia and crypto, as well as most viruses). In fact, as an emergency measure, it has been noted that international travellers can significantly lower their risk by using the hot water (as hot as your hand can stand) from the tap of hotel sinks (most hotels in foreign countries do not have the 120F limitation on hot water that we do in the US - this is lower, not eliminate). One clarification I will add is this - since most people do not carry a thermometer into the back country to determine the water temperature, to be safe, raise the water to a boil. This is not when bubbles start forming in the water on the bottom and sides of the pot, but when a full rolling boil starts.

I will be giving the references later. But for a quick reference in a single compendium, you can refer to Paul Auerbach's book Wilderness Medicine (the 5th edition has come out recently with updated information). The book itself is huge enough that you need the DVD-rom that goes with it to readily search the references.

I have noticed that when discussing giardia & cryptosporidium some product literature uses the term "kill" and some use the term "inactivate".

I have also read that iodine does not "kill" crypto, however it seems to me if all you need to do is "inactivate" giardia & crypto so it can not reproduce and make you sick then the iodine would be effective against crypto.

It has in the past seemed to me that this is purely a game of semantics between competing brands of chemical water treatments.

Or am I all wet?

You are correct that there is a lot of semantic gaming involved. There are technical meanings to "disinfection", "purification", "potable", "inactivate", and "sterilization" that are not necessarily obvious to the non-technically educated consumer. For example, "potable" means "drinkable" with a statistical likelihood of illness that is "acceptable" (if I am the one who gets super-sick and have to be evacuated, it ain't acceptable, but if I'm the only one in a million, that's considered more than ok).

"Kill" means it is dead and the organism will cause no problems (some bacteria and other organisms generate waste products while alive that are not destroyed and will continue to make you very sick, salmonella being an example). Iodine will in fact kill crypto, given sufficient exposure time at a high enough concentration at the right pH, though the time required is fairly inconvenient. "Inactivate" means the organism goes dormant and will cause no problem for a while - bacterial cysts being an example - but will eventually become active again.

As for inactivate, UV (Steripen, for example) does kill most biota, but inactivates others for long enough to drink or use in food preparation safely, but does not have a lingering effect (as do halogens), so some of the critters can stir themselves back to dangerous levels if the water is left in the water bottle long enough.

There is a list, which I should reproduce here, of "claims" terminology that the CDC and EPA have placed requirements on and "claims" terminology that has no accepted meaning in a book I recently acquired on disaster survival.

I should note that the filter I use most, the Katadyn Hiker Pro, is intended for high-quality surface water in the US backpacking market. It is recommended by Katadyn (coincidentally riverridgeray's company) that halogen disinfectants be used for international travel or where high levels of contamination are possible, which includes events such as the recent Midwest flooding, Hurricane Katrina, or our occasional West Coast large earthquakes, where there may be a large increase in the content of viruses. From reviews like Backpacker publishes, you can get the impression that such filters are good anywhere, anytime, under any level of contamination.

I note that riverridgeray says that in 20 years, he has neveer seen a filter

irrepairably clog, break, or otherwise fail

Well, sorry, but I have seen failures with every brand of pump filter over the last 25-30 years. Maybe "irrepairably clog" does not include where you have a spare element to swap out, but I have seen every brand clog to where the filter element could not be cleaned by brushing or backflushing, notably in areas like Philmont Scout Reservation, where they run a couple thousand youth through per week during the 12 week summer season (my son was a Ranger there and reported the same thing to me). I have seen filter elements (especially ceramic) cracked by freezing when people neglected to make sure there was no water remaining when the temperature was dropping well below freezing, and seen them cracked in careless handling. Plus I have seen many broken pump handles, hoses getting so worn they would not stay on the hose bib (the push-on inlet or outlet), etc. Most of these failures were user errors and/or ignorance, but some were due to age or water laden with glacial flour or volcanic ash.

Note that my personal choices are boiling for water that I am cooking with (have to heat it anyway), Steripen for water that is sufficiently clear, filter with settling and prefiltering if there is turbidity, and halogens for quick and dirty desperation backup (iodine if I want the water fairly quickly, chlorine dioxide if I can wait the 4 hours). I haven't had a water-borne sick spell in several decades (actually none ever that I know of, though I got really sick from a shrimp cocktail served in First Class on an airline, along with all 5 of my travelling companions). But then, given the claim in riverridgeray's "ezine" article of most long-time hardy outdoors types being carriers, maybe I am just "Giardia Bill" or "Crypto Joe".

Bottom line - treat all your water by one or more means, and make sure your hands are clean either by soap and water or Purell before handling food or putting your hands near your mouth.

I have been using filters, followed by chemical treatment for about 20 yrs.
I also pay close attention to personal hygiene as well.

I currently use the Katadyn Hiker Pro with Micropur & the MSR Sweetwater Purification System with Viral Stop.

I like both systems, but anything with moving parts can and will fail under the right circumstances, and almost always when it is being used.
At least that has been my experience.

I should add that, if I know the water is really really contaminated, I use the Pur kit that is described at the end of the 4th installment. Since that works on 3rd World mudhole water, that should do it. Problem is, I am running very low on the chemical packets, so I am storing the remaining ones for a major natural disaster (or if I somehow get transported to Zimbabwe or Somalia). Alicia and I have had a lot of difficulty in dealing with the Pur distributor, and I don't know of a local source, other than the on-line ordering site. It would sure be great if somehow a large number of the kits could get shipped to those unfortunate countries, where the people are resorting to drinking water containing raw sewage.

Bill S. It appears the two parts of my posts that bothered you the most were.

1. My assertion that Iodine does not kill Cryptosporidium. I confess I could have stated that a little more lawyer-like. Let me try again.

Iodine does not kill Cryptosporidium when used according to manufacturer’s recommendations in any reasonable amount of time. Let me quote my source.
From: Wilderness and Environmental Medicine: Vol. 8, No. 2, pp. 96–100.
Efficacy of iodine water purification tablets against Cryptosporidium oocysts and Giardia cysts CHARLES P. GERBA, PhD; DANA C. JOHNSON, PhD; MICHAELA N. HASAN, MS

To sum up the above paper I'll use one quote:
"These data strongly suggest that iodine disinfection is not effective in inactivating Cryptosporidium oocysts in water. Because this organism is common in all surface waters, it is recommended that another method of treatment be used before ingestion”.

2. Boil time. I'll stay with "sterilization" and the recommendations of the CDC and EPA over other assertions. 1 minute up to 6,700 Ft. and 3 minutes above seems easy to achieve in most all situations.

Although I do more than my share of solo wilderness trips, maybe of my trips are multiday whitewater float trips. We commonly pump many gallons of water per day. When you have group of people on a multi-day river trip: those pumps get a workout.

I do see and hear about broken and clogged pumps from Katadyn and other brands. I will stick with my assertion that I have never been on a trip where the pump filter completely failed from clogging or breakage. I've done a lot of cleanning of prefilters and filters, lubrication of gaskets, and I do try to avoid really dirty water. But I've even pumped for 16 people on a 18 day Grand Canyon float without totally trashing my filters.

thanks for your interest! riverridgeray.

Bear with me. I wrote the above post in Word and then cut and pasted it in. There was some movement of words when it uploaded. Since health information is important. I will repeat the parts that are messed up.

Bill S. It appears the two parts of my posts that bothered you the most were.

1. My assertion that Iodine does not kill Cryptosporidium. I confess I could have stated that a little more lawyer-like. Let me try again. Iodine does not kill Cryptosporidium when used according to manufacturer’s recommendations in any reasonable amount of time.

Let me quote my source.

From: Wilderness and Environmental Medicine: Vol. 8, No. 2, pp. 96–100. Efficacy of iodine water purification tablets against Cryptosporidium oocysts and Giardia cysts


To sum up the paper:

"These data strongly suggest that iodine disinfection is not effective in inactivating Cryptosporidium oocysts in water. Because this organism is common in all surface waters, it is recommended that another method of treatment be used before ingestion”.


It serves no one to get into a p-ing contest. But some of your statements are a bit misleading. When you state flatly that iodine "does not kill" crypto, you are not correct. It is correct to say that crypto, especially in the oocyst form is highly resistant to iodine (and chlorine, for that matter). It is also correct to note that halogens are much less active at low temperatures (which are commonly encountered in mountain streams, the environment we are talking about) and if the pH departs significantly from 7.0. It is also correct to state that most backcountry travelers do not have the patience (and may be unaware) of the time required or of the time/temperature effect. This is no doubt what you are referring to in your comment about "any reasonable amount of time." It is not correct to state flatly, as you did, that iodine does not kill crypto. If you make that statement, you also have to state that chlorine, including in the form of chlorine dioxide, does not kill giardia (times of 4 hours and longer are not really very reasonable, with 8 to 12 hours being required for giardia cysts with water at the 35-40°F found in many mountain streams much of the year).

Since filters of 1 micron pore size (not just "effective pore size", but actual pore size) and smaller are effective at removing protozoa (like giardia and crypto) and many of the problem-causing bacteria, filters are a good first step. However, filters are ineffective against many viruses which are present in water in major rivers and lakes in the US and in most water sources in Third World countries, as well as disaster-disrupted water supplies anywhere. Halogens applied after filtration are effective against the majority of these viruses (the hepatitus and HIV groups are notable among these). Passing filtered water through an iodine resin matrix (which several of your company's filters used to have in the series purchased from Pur, and your bottle/straw still has) has been found to be effective for these viruses.

Your statements on boiling are the result of confusion of terminology. The medical and public health community designate several stages in reducing the effectiveness of contaminants in water. "Potable" means that the water is "drinkable" and that there is "minimal microbial hazard" so that the statistical likelihood of illness is acceptable. "Disinfection" is a process that kills or destroys nearly all disease-producing microorganisms except bacterial spores (some of which can survive for long periods in boiling water at 100°C/212°F). Basically, this is the goal for wilderness water treatment. "Purification" means the removal of organic or inorganic chemicals and particulate matter to improve taste, color, and odor. Note that the term "purification" is often used when "disinfection" is meant (including in my posts). "Sterilization" means that all microbial life, including bacteria, viruses, protozoa and spores are destroyed. At this stage, the water can be used for surgical purposes. The CDC and EPA recommendations for boiling times are intended to produce water sufficiently sterile for surgery and other medical procedures, with this specifically being to destroy hepatitis A . If the disinfected level reached at 155°F/70°C is not sufficient for you, then you should avoid pasteurized products like most commercially sold milk in the US (a number of European countries have sterile milk standardly in their stores). Protozoa like giardia and cryptosporidium are particularly vulnerable to temperatures of 140°F/60°C and higher. Look at Auerbach, Wilderness Medicine, 5th edition, p 1377 and the references listed there for a detailed discussion.

One note to be added in my revision of the articles will note that while streams in the Rocky Mountain, Cascade, and Sierra backcountry show an absence of giardia and cryptosporidium or a number of cysts per liter well below the level considered to pose a risk in the vast majority of samples, there are occasional spikes that do pose a significant risk, probably due to seasonal runoff, sporadic animal activity, and/or presence of humans who fail to practice basic sanitation. Therefore, at the minimum, it does not hurt to treat the water to be drunk (like wearing your seatbelt in the car or wearing your helmet on bike or skis, you may go for years with nothing happening).

Note well that I have not said anything remotely resembling "it's all safe, don't bother with treating the water." Instead, I am saying practice basic sanitation, since all the evidence shows that by far the major source of backcountry illness is failure to wash or disinfect your hands or your food handler's hands, while at the same time taking basic precautions with the water you use for drinking and with your meals. Prevention is far better than the cure, and the cure may be days away from where the problem arises.

Yeah, what Bill said.

I used to own and use the PUR purifier with a prefilter, charcoal top, and filter with a iodine resin matrix. It was a great filter I thought.

There does not seem to be a backpackers filter on the market like that now, were there liability issues with claims made or what's the deal with that? Or am I overlooking a product?

Currently I both filter, and treat chemically, just 'cause I want to play it safe. Being real sick on a solo trip is no fun, not to mention that you can get sick days after a trip as well.

I take soap & Purell or equivalent, I don't see the reason to filter or boil water when you have contaminated all your gear (like your filter hoses, water bottles, cup, etc.) with nasty hands.

And yeah, they are nasty after a couple days with no washing.

Bill, riverridgeray--

Seems to me that both of you are knowledgeable and have lots of good information to share. As an MD, and having read the articles involved, the comments, etc., I'll go so far as to say that you have both in general taken reasonable, responsible opinions. The type of disagreement arising here is a not uncommon one in the medical and scientific fields. In a Journal Club discussion of even a highly reputable article, the fur may fly with abandon at times. So, in the interest of harmony, world peace, and reduction of carbon dioxide emissions, may I suggest that you both take a deep breath, count to ten, and then respond as if your mother were watching?

I'm not intending to be paternalistic or whatnot, just hoping to help keep the peace between what I perceive as two well-meaning individuals. If I've offended one or both of you, I apologize.

Just to give you both opportunity to redirect yor fire, however, consider this: Giardia is not nearly the risk that it is generally made out to be, nor is cryptosporidium, for most folks. Absolute safety whilst ingesting water in any locale is impossible. Therefore, the reasonable person will seek to make the risks "reasonable" to him. As far as I can tell, the approaches you both advocate are reasonable. I don't routinely follow either one. (So there, hah!)

Note to anyone reading--this does not constitute medical advice regarding water ingestion, potability, purification, sterilization, or any of those things. If you wish to obtain medical advice appropriate to your health and circumstances, see your personal health care provider.

consider this: Giardia is not nearly the risk that it is generally made out to be, nor is cryptosporidium, for most folks. Absolute safety whilst ingesting water in any locale is impossible. Therefore, the reasonable person will seek to make the risks "reasonable" to him. As far as I can tell, the approaches you both advocate are reasonable....

Well, Perry, I do not advocate any particular approach for water treatment (although I do advocate being sanitary when it comes to personal hygiene and especially for the food preparers). The point of my articles was to present the information that is out there, as it relates to North American backpacking areas, so that people would know the alternatives and could choose for themselves. I have no system to promote (unlike ridgeriver, who is a Katadyn representative). I listed some (but not all) the advantages and disadvantages of each approach (boil, chemical, UV, coagulation/flocculation). My problem with ridgeriver's posts is with his dogmatic statements that disagree with the wilderness medicine community's research (I relied on several of the people who seem to be considered the leading experts for reviewing what I wrote).

I completely agree with your statements that the risks of giardia and crypto are overblown for most people in most of the backcountry in the US, and that complete safety is impossible. Some people have other health issues and should take extensive precautions, of course. And, as I said, it doesn't matter if the odds are 0.0000001 of getting one of the waterborne diseases if I am that one person. If I am not comfortable with those odds, then I should take extra precautions - belt and suspenders, so to speak. Since no one system takes care of all the risks (viruses get through filters, crypto is resistant to halogens especially for the cold water coming from streams, UV does not have a ligering effect, some bacterial spores will survive boiling water...) as I stated, it is reasonable to take a multiprocess apprach, if that makes me more comfortable (still keeping in mind that this is still not perfect).

Hopefully, having the information that is out there in the wilderness medicine community will allow people to make a more or less rational choice without succumbing to the scary ads of the companies selling products.

I suspect there is a lot of truth to the statement that a number of long-time backcountry travellers may have resistance or some level of immunity to many of the waterborne illnesses (and may be carriers, in turn). I have had the experience of being on climbing expeditions where 2 or 3 of the party got very sick, while the rest of us suffered nothing at all, despite eating the same food and sleeping in the same tent. Maybe part of that in my case came from growing up in fairly primitive conditions in the Arizona desert, coupled with living for a while at a very young age in Central America and our family travelling a lot in Mexico. I see these articles claiming that one reason so many children have allergies these days is that they are so protected from exposure to "germs" that their immune systems do not develop as well (I also suspect this is one of those areas you referred to with your comment on vigorous debate, even on well-refereed articles in professional journals).


Thanks for the reply. I think you're spot on with both your approach and description of methods, options, etc. And I'll certainly acknowledge that riverridgeray might have a different dog in the fight. I just kinda wanted to remind all that making decisions about water filtration/treatment, etc. isn't something wherein there's always only one "right answer". And I'd certainly echo your comment that it's almost always more important to practice good, clean food preparation techniques and proper personal hygiene.


Thanks, btw, for preparing the article series. Quite good, I thought, and I'll be referring folks to it for their own edification.


BTW, you're right about the childhood allergy thing being one of those topics that can get people riled up. And we won't even talk about immunizations! Whew!


Does anyone have experience with the Lifesaver bottle? After reading a bunch of articles and the tech info it seems like a pretty incredible filter. Unfortunately it's not mentioned in this article. Is it too new and untested? Claims to filter down to 15 nm (.015 microns) which is smaller than the smallest virus. It's a big bottle but not heavier than the Katadyn Pocket or Combi filter which only filter down to 200nm (.2 microns.)

Those who find themselves in areas where viruses are common typically tend to treat with chlorine tablets. Filters small enough to catch viruses are going to have a much shorter useful life and are going to cost more than your average bacterial and protozoa filter. It just makes better sense to use two treatment methods in most cases.

My knowledge of the Lifebottle is limited, but from what I gather it's being marketed as a charitable gift to under-developed regions where modern sewage treatment isn't a reality. There is some minimal knowledge required in filtering and treated especially dangerous water sources, which is what I believe the Lifebottle is trying to eliminate. By providing one simple device that removes or neutralizes all contaminants they're helping to improve the health of those who have little choice to life in those areas.

That being said, gear reviews are great and great gear reviews are awesome. If you have one in your posession and have a desire to use it, go ahead and put it through its paces and write all about it. Then post it on Trailspace!

I just purchased a collider silver generator. I also have a couple of ounces of silver in my backpack. I need to get a small nine volt solar panel so I can treat water in the field. Batteries will work but I can't recharge them.

The settlers tossed a silver coin into a bucket of water overnight to purify the water. I am pretty sure it will still work today.

Silver does indeed work, but has an incredibly long contact time to actual purify a large amount of water. Research shows that for a silver coin the size of a modern day quarter it would take about 4-6 hours per liter. And the time will increase based on the temperature and amount of sediment etc in the water.

A common practice in remote villages is to use a combination of silver and UV treatment.

Russia has been putting large blocks of silver into village wells in remote areas for a long long time.

....Research shows that for a silver coin the size of a modern day quarter it would take about 4-6 hours per liter. ...

Not to mention that the currently issued US coins have no silver (dime, quarter, half dollar, and silver dollar are copper and nickel, penny is only copper plated, and the nickel is 75% copper, 25% nickel).

That's interesting, I didn't know that silver could be used to purify water like that. I knew it was used in wound dressings and as an antiseptic.

TheRambler said:

....Research shows that for a silver coin the size of a modern day quarter it would take about 4-6 hours per liter. ...

Not to mention that the currently issued US coins have no silver (dime, quarter, half dollar, and silver dollar are copper and nickel, penny is only copper plated, and the nickel is 75% copper, 25% nickel).

This is what happens when you let spoiled rich kids run an economy.

DrReaper, can you please explain the silver water treatment process more thoroughly? You have definitely peaked my interest.

The settlers that crossed the planes tossed a silver coin into their wooden buckets to disinfect their water. It takes hours to days to do it that way and it still works.

I have a cheep $30 collider silver generator in my pack. It runs off of a 9 volt battery. Using electrolysis it makes collider silver water. You can read all about that on the web. It should be pretty well decontaminated at that point.

I want to get a few solar cells to eliminate the battery so I can run it all the time.

I am not sure what the effects are from living off collider silver for an extended amount of time. I think your skin may change color literally.

Wikipedia on medical uses of silver:

What can happen if you ingest too much colloidal silver:

When I used to hike the Grand Canyon, I used to carry Gatorade to mix into my water. Often times it was untreated and I did not use a water filtration system. All I added was the Gatorade and drank it.

Do you think its possible for some one to be able to grow up drinking natural water and never treating it, so that eventually the body builds some sort of natural defense to untreated water? I grew up on a farm in upstate New York, I grew up drinking untreated well water till I was 16. Then when I started hiking at age 21 I never used water filters anywhere I hiked and have had but a few times when water got me sick.

I hiked the Grand Canyons backcountry for 20 years and never treated the water with anything besides Gatorade. My theory was that the citric acid in the drink mix neutrized the water?

Can anyone explain how this worked otherwise. The only time I got sick from drinking untreated water was in Tucson when I had ingested water at Tanque Verde Falls while diving into the water. The next day I woke with a terrible feeling in my gut. I had to call in sick to work and went to the hospital. The said I had microrganisms in my intestines that were making me sick. They asked if I had drank any untreated water, I told them no but had been diving into Tanque Verde pools the day before and had ingested water as I dove in. It took about two days for the discomfort to go away.

I have been hiking around the southern California desert for years. I drink the water without treatment when I was young. I never got sick. I may have just been lucky.

SnowGoose: I think that is the guy who beat cancer using collider silver. It didn't say anything about it in the interview but I am pretty sure that is the guy.

Do you think its possible for some one to be able to grow up drinking natural water and never treating it, so that eventually the body builds some sort of natural defense to untreated water?

I personally think that's possible. On many trips into the Yucatan of Mexico we would find wells next to latrines or downstream from latrines. When we asked locals about overall health of those that lived in the jungle around it, there were no issues. We always carried our own water then on those 2-3 day trips and never used that water to clean up in.

And I have a good friend who grow up in Colorado. Thy never used any public water works, but always drank water from their own wells and when in the backcounrty meerly drank from streams with out purifing it first. She was born in 1957and untill she moved away from home to come to Jackson Hole in the early 80s always drank from water every source of running water or wells. She now has lived in Jh for 30 year and whn she goes hiking drinks dierectly from streams, creeks and springs in the JH highcountry with no ill effects.

When I was in Yosemite in 2002, I went to get a permit to hike the Yosemite Falls to Tenya Lake Trails and the ranger asked what kind of water treatment I used. I said I did not carry anything. So she asked "so you boil it or add something?" I said no I dip my Sierra cup in and drink. She told me if I got sick not to blame the park service!

In the backcountry of the Grand Canyon where I spent 20 years hiking from October to March, all the water is from springs or the Colorado River. I drank freely without anything but Gatorade mix in the water. After a while I wasu cautious not to drink directly from water sources in front of others as they would always ask if it was okay, and I did not want to make them think it was and then get sick.

I would usually get sick from city water when I would come back into towns to work after being in the backcountry drinking water untreated for 6 months. It usually took me a couple weeks after returning to towns to get used to the city water.

I stumbled upon this fun fact today while poking around the Sawyer website: 

For viruses to be present at least one of the following conditions is usually present in the water:

1. Human or animal waste in the water
2. Dead animals in the water
3. Slow or stagnant water
4. Water temperatures above 50 degrees F

..figured it was worth passing along.


As the frequent contrarian (although here maybe not so contrary) here is my two cents worth:

The whole spiel about filtering wilderness water is unnecessary for the most part, at least in the western half of the nation.  I think the huge concern to use any treatment is a result of misguided fears over the statistically improbable occurrence of getting sick from water borne bugs, and Madison Avenue pitching their wares to the gullible masses.

There are water quality surveys conducted on an ongoing basis in the Sierra Nevada that indicate most water sources there are at least as free of harmful organisms as your typical city water.  Research based on these surveys concluded the only areas that seem to warrant caution are watershed with heavy human backcountry presence, and areas with a lot of equestrian or bovine activity.  But surprisingly the list of hot spots is rather limited, and did not include some areas I would have assumed otherwise. This same research also supports Bill’s assertions that much of what passes as water borne illnesses are most likely personal hygiene issues.

For what it is worth I used filtration for only for two seasons in my forty years of camping throughout the Sierras, Rockies, Cascades, and Alaskan ranges.  I quit using filters because I found glacier silted water and freezing issues made the technology a hassle to use.  Besides I had better things to do than operate a pump for thirty minutes a day.  I currently carry a two part chemical sterilizer that is marketed to marine sports enthusiasts, which has a treatment time that is almost instantaneous, baring suspended particulates (in which case they recommend a four hour pickling time).  But I only treat my water in areas known for questionable water quality, such as the Grand Canyon, Peru, etc. or when a chosen camp site appears to have risk issues, as described above.  That said I rarely treat my water.

Like Bill, I have yet to get sick from bad water despite the thousands of gallons of untreated water I have ingested in my life time.  It does help, however, to avoid obvious questionable sources such as waters with proximal upstream trail crossings, brackish ponds, etc.  I make a concerted effort to seek camp locations with water sources that are either percolating out of the mountain as head water, or have a vigorous flow.   It’s all about knowing your water sources – and washing your hands prior to handling anything that goes into your mouth!


Hi ,
I think that colloidal silver will be safe if it taken within a specific limits .
Here is a blog that contain very useful information about colloidal silver uses .


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