I was prompted by another current thread here on W&SS to share something that I have. About 12 years ago I participated in an online discussion (on another forum) with the water filter developer from MSR. We had some offline communication as well. I was persistent enough ion my questions that he shared some things with me that were not part of the online discussion. One was a full water filter test report. Another was the article I will post below, which I subsequently found on the Marathon Ceramics web site, the company who was making the ceramic elements for MSR.
Although some parts of this are clearly marketing, and this is dated (it does not discuss chlorine dioxide or UV lamps), it contains a lot of good discussion about water quality in general.
I'll post this in several parts since it is fairly long.
Portable Water Filters: a Designers Perspective
Dan Vorhis
version 7-30-97A
Most people know by now the advantages of carrying a portable water filter. Filters usually weigh less than carrying water and deliver drinking water quickly, with relatively little effort. And even if available surface water is cloudy, filtered water is usually pretty clear. Until about six years ago, you would find one or two "old-faithful" portable water filters to choose from on the shelf under the bike pumps. Now you go in a store and cant miss a huge display with a dozen likely-looking devices sitting in a prominent place beside an aquarium from which to pump. The backpacker has benefited from all these new product introductions - filters are easier to use and less expensive than ever before. But the added selection and marketing pressure has left a lot of people bewildered or, worse yet, has created product gurus who would answer your questions based on a casually-informed article or on persistent marketing hype.
One thing different about water filters compared to, say, stoves or snowshoes - you cant really tell if they work. Yes, you can see if they pump water easily. You can see if they seem to be well designed. You can read the reports about clogging rate, or even find out for yourself how fast they clog. But you cant really tell if they are protecting your health adequately. It is so intimidating an issue that even the backpacking journals have avoided questioning the effectiveness of devices, choosing instead to parrot manufacturers claims on well laid-out charts.
This paper describes my perspective on recent issues related to portable water filters, based on my experience as a designer of water treatment devices for Mountain Safety Research, Inc. These observations are probably not entirely objective, or at least a competitor of MSRs might make that case! You will probably notice a definite lean toward microfiltration here, a position which I think is justifiable.
What can make you sick?
Microorganisms.
It is estimated that about 1/3 of human illnesses in the world are caused by drinking contaminated water or eating contaminated food. According to recent reports, in the U.S., microorganisms (protozoa, bacteria, viruses) account for about 40% of waterborne illness, non-living or "chemical" contaminants account for about 10%, and the cause of the remaining 50% have not been identified. These statistics are gathered by the Center for Disease Control and Prevention (CDC), and others, from outbreaks mostly associated with community water treatment systems. Nobody does a very good job of tracking what makes backcountry travelers sick.
The "50% unknown" is interesting. Many of what are now known to be major waterborne pathogens (microorganisms that make you sick), such as Giardia, Cryptosporidia, and Campylobacter jejuni, were discovered to be human pathogens within the past 20 or 30 years. There are sure to be more "discovered" in the future.
Your friend may drink improperly-treated water and never show symptoms, while you drink the same water and are nauseous for weeks. Or the scenario might be reversed after your friend hasnt gotten enough sleep for a week, and is under the gun at work. Our ability to resist infection from bad water varies with age, stress, what weve eaten for lunch. Children are often more susceptible than healthy adults, as are older people and people with weaker immune systems.
For example: In a Baltimore, Maryland, study, healthy young adult volunteers were fed various doses and strains of a bacterium called Campylobacter jejuni. Campy is a bacterium found worldwide, including in the backcountry. When volunteers were fed 800 bacteria, 10% became ill with diarrhea and fever, 50% showed evidence of infection with no symptoms. When the dose was increased to 90,000 organisms, 46% became ill, and 85% showed evidence of infection.
Bacteria. Bacterial symptoms, if they appear, come about 6 hours to 3 days after exposure. Symptoms include "explosive" diarrhea, vomiting, fever, headache, dizziness, weakness, sometimes bloody stools. For most healthy adults, bacterial infections are self-limiting, and symptoms disappear after 3 or 4 days, although a small percentage of people will remain ill for weeks. Often, immunity against re-infection is maintained as a sort of compensation for all the fun. For example, in the Campy study mentioned above, seven volunteers who had experienced illness, and twelve who hadnt, were re-challenged one month later with 100,000,000 Campy bacteria. (Yummy. Actually, you wouldnt see or taste this quantity of bacteria in the water.) None of the veterans showed symptoms, while six of the "controls" paid their dues. It can be seen why a grim harvest of young children (death by dehydration) takes place each year in places where high quality drinking water is unknown - the kids havent had a chance to build up any immunity.
Protozoa. Protozoan infections usually take longer to show symptoms - one week to several months. Giardia cysts "hatch" after a period of time in the small intestine and reproduce, interfering with adsorption of nutrients and, in some people, causing symptoms such as diarrhea, gas, cramps, weight loss, weakness, nausea. Symptoms of Giardiasis usually appear 1 to 8 weeks after ingestion of the cyst. Without treatment, Giardiasis infection will continue for two or three months in most people, and can permanently scar intestines.
The protozoa Cryptosporodia parvum may cause copious watery diarrhea, cramps, nausea, vomiting, low-grade fever usually 1 to 2 weeks after exposure. The illness lasts for 7 to 20 days in "immunologically healthy" adults. "Crypto" has been getting a lot of press lately following about a dozen recent worldwide outbreaks. The largest outbreak so far occurred in Milwaukee, Wisconsin in 1993 - an estimated 403,000 ill, around 100 deaths. In its cyst form, Crypto is incredibly resistance to chemicals like chlorine and iodine. In one study, Crypto oocysts (the environmentally resistant form of Crypto) were able to infect mice after soaking 24 hours in straight household bleach! This organisms resistance to iodine is one of the reasons why the U.S. Marines have stopped relying on iodine tablets for water treatment. Crypto oocysts are smaller than Giardia cysts (see Figure 1). They can break through sand filtration at water treatment plants and make people sick even when the plants are working as they should. Infectious dose (how many organisms it takes to make you sick) is thought to be quite low, some say as low as one oocyst, for this organism. There is no known cure for Cryptosporidiosis - once youve got it, you have to suffer through it.
In a sampling of 257 water samples from 17 states (Rose, Gerba, Jakubowski 1991), Crypto oocysts were detected in 55% of surface water samples, with an average concentration of 43 oocysts/100 liters. Giardia cysts were found in 16% of the same samples, with an average concentration of 3 cysts/100 liters. Pristine waters seem to be less affected than lowland waters exposed to urban and agricultural run-off. Young calves are a major reservoir - the CDC estimates that 90% of dairy farms are infected with the cyst.
The USEPA is currently overseeing an even more thorough investigation of the microbiological state of surface water sources used by communities for water treatment. Out of this study will come more reliable information about the concentration of viruses, bacteria and protozoa in these waters. There have been questions about the reliability of previous studies because of examination methods used. The current exhaustive effort should deliver the most accurate picture yet.
Viruses. Waterborne viruses that make people sick usually originate from human fecal material. This differs from bacterial and protozoan pathogens, many of which cross species freely, and are therefore carried in the backcountry not only by humans, but by animals including small rodents and deer. Viruses do not reproduce in surface water like some bacteria. Most virus particles "die" (there is some question about whether they were actually alive in the first place) within days of exposure to the environment. Nevertheless, an individual may become infected after ingesting only a few virus particles. Anywhere there are infected humans and the chance of human fecal contamination, there is the chance of viral infection.
Illness from waterborne viruses takes many forms. Hepatitis A, spread through fecally contaminated food or water, is a highly contagious liver disease with symptoms that include yellow skin and eyes, dark-colored urine, flu-like symptoms (fever, chills, weakness), stomach pains. Young children often show no symptoms, and about half of adults who become infected show no symptoms. Illness from Hepatitis A, if it occurs, appears two to six weeks after exposure, and may require 6 months for complete recovery. Note that there are other Hepatitis (inflaming the liver) viruses like Hepatitis B and C, spread through contact with bodily fluids, not through drinking water.
Rotavirus is another common waterborne virus, with symptoms more similar to bacterial infections; vomiting, watery diarrhea, low-grade fever. Rotavirus infection is one of the most frequent causes of severe dehydrating diarrhea in children. Spread of the disease occurs not only through drinking fecally-contaminated water, but also through contact with utensils and objects that come into contact with feces.
Note that few water treatment facilities in the world routinely check for viruses in their water supply. Some cities - along the Ohio and Missouri rivers, for example - rely on water that has been "previously used" by citizens upstream. During low water times, a glass of water might quench more than one thirst on its way to the ocean. Viruses have been detected in community water systems along these routes. Another "home use" water source, well water, has also come under scrutiny. Apparently, household wells are sometimes located too close to septic systems, and viruses can find their way into drinking water more or less easily, depending on soil conditions.
"Chemical" contaminants.
This class of contaminant is often conveniently ignored in the portable device industry because most waterborne illness is caused by microorganisms, and illness caused by chemicals rarely causes acute symptoms, making tracking difficult. This class of contaminants can also be a problem for portable devices to deal with - a few grams of granular carbon doesnt do it. What kinds of chemicals can make you sick?
Pesticides are usually associated with urban or agricultural run-off. This can mean aerial sprays in backcountry timber stands. Concentrations of various pesticides in surface water go up in the early growing season as a result of higher application rates and more rains.
Bacterial Toxins are produced by what used to be called blue-green algae, now called cyano-bacteria, which bloom in warm water and form greenish soup. Other toxin-forming organisms are thought to occur on snow ("watermelon snow"). Filtering out the algae does not remove the toxin in the water. Such toxins have been known to kill large animals within minutes. Adequate contact with quality activated carbon has been shown to greatly reduce concentrations of bacterial toxins. Inorganic contaminants like mercury and arsenic dont just enter surface water through industrial run-off. In the big, dry interior basins in western U.S., for example, low rainfall allows accumulation of metals and minerals in valley surface water. Drainage from mine tailings can also contribute. Some of these contaminants are tough to remove even with a block of high quality activated carbon. Halogens such as iodine and chlorine, used in water treatment, are toxins in sufficient concentration, or create toxic by-products when they react with natural organic materials in surface water.
Some common misconceptions about the causes of waterborne illness.
"Giardia is mostly what I have to worry about in the backcountry, right?"
It surprises me how many people who should know better - microbiologists at the health department, for example - continue to spread this tale. Cryptosporidia is obviously another backcountry threat. The tiny bacteria Campylobacter jejuni is also a concern. A study in the early 1980s found 23% of patients showing up at a clinic near Grand Teton National Park were infected with Campy (compared to 8% infected with Giardia). Last summer (1996), another such clinic reported seeing about two Campy-caused illnesses for every one illness caused by Giardia. There are certainly other bacteria and protozoa in the backcountry, carried by animals and humans and transported into surface water from feces, that cause human illness.
"Viruses are the major health concern outside the U.S."
Food and water borne disease are the number one cause of illness in travelers, according to the Center For Disease Control and Prevention (CDC), and "travelers diarrhea" is the most frequent health problem. According to the CDC, " Although viruses are commonly acquired by travelers, they do not appear to be frequent causes of Travelers Diarrhea in adults." Bacterial infections from contaminated food or water, especially from toxic strains of Eschericia coli, Salmonella species, Shigella species, and Campylobacter jejuni, cause most of the diarrhea.
Although some parts of this are clearly marketing, and this is dated (it does not discuss chlorine dioxide or UV lamps), it contains a lot of good discussion about water quality in general.
I'll post this in several parts since it is fairly long.
Portable Water Filters: a Designers Perspective
Dan Vorhis
version 7-30-97A
Most people know by now the advantages of carrying a portable water filter. Filters usually weigh less than carrying water and deliver drinking water quickly, with relatively little effort. And even if available surface water is cloudy, filtered water is usually pretty clear. Until about six years ago, you would find one or two "old-faithful" portable water filters to choose from on the shelf under the bike pumps. Now you go in a store and cant miss a huge display with a dozen likely-looking devices sitting in a prominent place beside an aquarium from which to pump. The backpacker has benefited from all these new product introductions - filters are easier to use and less expensive than ever before. But the added selection and marketing pressure has left a lot of people bewildered or, worse yet, has created product gurus who would answer your questions based on a casually-informed article or on persistent marketing hype.
One thing different about water filters compared to, say, stoves or snowshoes - you cant really tell if they work. Yes, you can see if they pump water easily. You can see if they seem to be well designed. You can read the reports about clogging rate, or even find out for yourself how fast they clog. But you cant really tell if they are protecting your health adequately. It is so intimidating an issue that even the backpacking journals have avoided questioning the effectiveness of devices, choosing instead to parrot manufacturers claims on well laid-out charts.
This paper describes my perspective on recent issues related to portable water filters, based on my experience as a designer of water treatment devices for Mountain Safety Research, Inc. These observations are probably not entirely objective, or at least a competitor of MSRs might make that case! You will probably notice a definite lean toward microfiltration here, a position which I think is justifiable.
What can make you sick?
Microorganisms.
It is estimated that about 1/3 of human illnesses in the world are caused by drinking contaminated water or eating contaminated food. According to recent reports, in the U.S., microorganisms (protozoa, bacteria, viruses) account for about 40% of waterborne illness, non-living or "chemical" contaminants account for about 10%, and the cause of the remaining 50% have not been identified. These statistics are gathered by the Center for Disease Control and Prevention (CDC), and others, from outbreaks mostly associated with community water treatment systems. Nobody does a very good job of tracking what makes backcountry travelers sick.
The "50% unknown" is interesting. Many of what are now known to be major waterborne pathogens (microorganisms that make you sick), such as Giardia, Cryptosporidia, and Campylobacter jejuni, were discovered to be human pathogens within the past 20 or 30 years. There are sure to be more "discovered" in the future.
Your friend may drink improperly-treated water and never show symptoms, while you drink the same water and are nauseous for weeks. Or the scenario might be reversed after your friend hasnt gotten enough sleep for a week, and is under the gun at work. Our ability to resist infection from bad water varies with age, stress, what weve eaten for lunch. Children are often more susceptible than healthy adults, as are older people and people with weaker immune systems.
For example: In a Baltimore, Maryland, study, healthy young adult volunteers were fed various doses and strains of a bacterium called Campylobacter jejuni. Campy is a bacterium found worldwide, including in the backcountry. When volunteers were fed 800 bacteria, 10% became ill with diarrhea and fever, 50% showed evidence of infection with no symptoms. When the dose was increased to 90,000 organisms, 46% became ill, and 85% showed evidence of infection.
Bacteria. Bacterial symptoms, if they appear, come about 6 hours to 3 days after exposure. Symptoms include "explosive" diarrhea, vomiting, fever, headache, dizziness, weakness, sometimes bloody stools. For most healthy adults, bacterial infections are self-limiting, and symptoms disappear after 3 or 4 days, although a small percentage of people will remain ill for weeks. Often, immunity against re-infection is maintained as a sort of compensation for all the fun. For example, in the Campy study mentioned above, seven volunteers who had experienced illness, and twelve who hadnt, were re-challenged one month later with 100,000,000 Campy bacteria. (Yummy. Actually, you wouldnt see or taste this quantity of bacteria in the water.) None of the veterans showed symptoms, while six of the "controls" paid their dues. It can be seen why a grim harvest of young children (death by dehydration) takes place each year in places where high quality drinking water is unknown - the kids havent had a chance to build up any immunity.
Protozoa. Protozoan infections usually take longer to show symptoms - one week to several months. Giardia cysts "hatch" after a period of time in the small intestine and reproduce, interfering with adsorption of nutrients and, in some people, causing symptoms such as diarrhea, gas, cramps, weight loss, weakness, nausea. Symptoms of Giardiasis usually appear 1 to 8 weeks after ingestion of the cyst. Without treatment, Giardiasis infection will continue for two or three months in most people, and can permanently scar intestines.
The protozoa Cryptosporodia parvum may cause copious watery diarrhea, cramps, nausea, vomiting, low-grade fever usually 1 to 2 weeks after exposure. The illness lasts for 7 to 20 days in "immunologically healthy" adults. "Crypto" has been getting a lot of press lately following about a dozen recent worldwide outbreaks. The largest outbreak so far occurred in Milwaukee, Wisconsin in 1993 - an estimated 403,000 ill, around 100 deaths. In its cyst form, Crypto is incredibly resistance to chemicals like chlorine and iodine. In one study, Crypto oocysts (the environmentally resistant form of Crypto) were able to infect mice after soaking 24 hours in straight household bleach! This organisms resistance to iodine is one of the reasons why the U.S. Marines have stopped relying on iodine tablets for water treatment. Crypto oocysts are smaller than Giardia cysts (see Figure 1). They can break through sand filtration at water treatment plants and make people sick even when the plants are working as they should. Infectious dose (how many organisms it takes to make you sick) is thought to be quite low, some say as low as one oocyst, for this organism. There is no known cure for Cryptosporidiosis - once youve got it, you have to suffer through it.
In a sampling of 257 water samples from 17 states (Rose, Gerba, Jakubowski 1991), Crypto oocysts were detected in 55% of surface water samples, with an average concentration of 43 oocysts/100 liters. Giardia cysts were found in 16% of the same samples, with an average concentration of 3 cysts/100 liters. Pristine waters seem to be less affected than lowland waters exposed to urban and agricultural run-off. Young calves are a major reservoir - the CDC estimates that 90% of dairy farms are infected with the cyst.
The USEPA is currently overseeing an even more thorough investigation of the microbiological state of surface water sources used by communities for water treatment. Out of this study will come more reliable information about the concentration of viruses, bacteria and protozoa in these waters. There have been questions about the reliability of previous studies because of examination methods used. The current exhaustive effort should deliver the most accurate picture yet.
Viruses. Waterborne viruses that make people sick usually originate from human fecal material. This differs from bacterial and protozoan pathogens, many of which cross species freely, and are therefore carried in the backcountry not only by humans, but by animals including small rodents and deer. Viruses do not reproduce in surface water like some bacteria. Most virus particles "die" (there is some question about whether they were actually alive in the first place) within days of exposure to the environment. Nevertheless, an individual may become infected after ingesting only a few virus particles. Anywhere there are infected humans and the chance of human fecal contamination, there is the chance of viral infection.
Illness from waterborne viruses takes many forms. Hepatitis A, spread through fecally contaminated food or water, is a highly contagious liver disease with symptoms that include yellow skin and eyes, dark-colored urine, flu-like symptoms (fever, chills, weakness), stomach pains. Young children often show no symptoms, and about half of adults who become infected show no symptoms. Illness from Hepatitis A, if it occurs, appears two to six weeks after exposure, and may require 6 months for complete recovery. Note that there are other Hepatitis (inflaming the liver) viruses like Hepatitis B and C, spread through contact with bodily fluids, not through drinking water.
Rotavirus is another common waterborne virus, with symptoms more similar to bacterial infections; vomiting, watery diarrhea, low-grade fever. Rotavirus infection is one of the most frequent causes of severe dehydrating diarrhea in children. Spread of the disease occurs not only through drinking fecally-contaminated water, but also through contact with utensils and objects that come into contact with feces.
Note that few water treatment facilities in the world routinely check for viruses in their water supply. Some cities - along the Ohio and Missouri rivers, for example - rely on water that has been "previously used" by citizens upstream. During low water times, a glass of water might quench more than one thirst on its way to the ocean. Viruses have been detected in community water systems along these routes. Another "home use" water source, well water, has also come under scrutiny. Apparently, household wells are sometimes located too close to septic systems, and viruses can find their way into drinking water more or less easily, depending on soil conditions.
"Chemical" contaminants.
This class of contaminant is often conveniently ignored in the portable device industry because most waterborne illness is caused by microorganisms, and illness caused by chemicals rarely causes acute symptoms, making tracking difficult. This class of contaminants can also be a problem for portable devices to deal with - a few grams of granular carbon doesnt do it. What kinds of chemicals can make you sick?
Pesticides are usually associated with urban or agricultural run-off. This can mean aerial sprays in backcountry timber stands. Concentrations of various pesticides in surface water go up in the early growing season as a result of higher application rates and more rains.
Bacterial Toxins are produced by what used to be called blue-green algae, now called cyano-bacteria, which bloom in warm water and form greenish soup. Other toxin-forming organisms are thought to occur on snow ("watermelon snow"). Filtering out the algae does not remove the toxin in the water. Such toxins have been known to kill large animals within minutes. Adequate contact with quality activated carbon has been shown to greatly reduce concentrations of bacterial toxins. Inorganic contaminants like mercury and arsenic dont just enter surface water through industrial run-off. In the big, dry interior basins in western U.S., for example, low rainfall allows accumulation of metals and minerals in valley surface water. Drainage from mine tailings can also contribute. Some of these contaminants are tough to remove even with a block of high quality activated carbon. Halogens such as iodine and chlorine, used in water treatment, are toxins in sufficient concentration, or create toxic by-products when they react with natural organic materials in surface water.
Some common misconceptions about the causes of waterborne illness.
"Giardia is mostly what I have to worry about in the backcountry, right?"
It surprises me how many people who should know better - microbiologists at the health department, for example - continue to spread this tale. Cryptosporidia is obviously another backcountry threat. The tiny bacteria Campylobacter jejuni is also a concern. A study in the early 1980s found 23% of patients showing up at a clinic near Grand Teton National Park were infected with Campy (compared to 8% infected with Giardia). Last summer (1996), another such clinic reported seeing about two Campy-caused illnesses for every one illness caused by Giardia. There are certainly other bacteria and protozoa in the backcountry, carried by animals and humans and transported into surface water from feces, that cause human illness.
"Viruses are the major health concern outside the U.S."
Food and water borne disease are the number one cause of illness in travelers, according to the Center For Disease Control and Prevention (CDC), and "travelers diarrhea" is the most frequent health problem. According to the CDC, " Although viruses are commonly acquired by travelers, they do not appear to be frequent causes of Travelers Diarrhea in adults." Bacterial infections from contaminated food or water, especially from toxic strains of Eschericia coli, Salmonella species, Shigella species, and Campylobacter jejuni, cause most of the diarrhea.