From: email@example.com (Eugene N. Miya)
Subject: [l/m 9/25/92] Water filters & Giardia Distilled Wisdom (9/28) XYZ
Organization: NAS Program, NASA Ames Research Center, Moffett Field, CA
Date: Sat, 9 Jan 93 12:20:20 GMT
Reply-To: firstname.lastname@example.org (Bill Tuthill)
[Comparison of filters, boiling and iodine]
Filters: First Need, Katadyn,
Iodine: PolarPure, Potable-Aqua
1991 – 1992
Based on “Medicine for Mountaineering”, owner’s manuals and
personal experience of author
Memo from Center from Disease Control
Dennis D. Juranek
Chief, Epidemiology Activity
Parasitic Diseases Branch
Division of Parasitic Diseases
Centers for Disease Control
c. Back-country water treatment to prevent giardiasis.
American Journal of Public Health
December 1989, Vol 79, No 12, pp 1633-1637.
Copyright 1989 AJPH 0090-0036/89$1.50 [used without permission]
Filters: First Need, H2OK, Katadyn, Pocket Purifier, Water Purifier
Chemicals: Polar Pure, Coghlan’s Emergency Germicidal Drinking
Water Tablets, Potable Aqua, 2% iodine,
Sierra Water Purifier, Halazone, commercial liquid bleach
Jerry E. Ongerth, PhD, PE,
Ron L. Johnson,
Steven C Macdonald, MPH,
Floyd Frost, PhD,
Henry H. Stibbs, PhD
d. REI Water Filter Chart (2 similar articles)
Comparison of specs: pore size, weight, capacity, filter life,
cost/gallon, price, replacement cost,
Filters: Katadyn, MSR, PUR, First Need, Basic Designs, Timber Line
Copyright (c) 1991 by Bill Tuthill
Unpurified drinking water may contain four things that pose health risks:
protozoan parasites (e.g. giardia), toxic bacteria, harmful viruses, and
poisonous chemicals. Of the methods available in the field, only boiling
and iodine are entirely effective against the first three, and only charcoal
filtration is effective against the fourth.
The First Need(R) water filter is cheap (less than $40), but is effective
merely against protozoan parasites. Its .4 micron filter pores are smaller
than giardia cysts at 3.5 microns, but larger than some bacteria, such as
E. coli at .3 to .9 microns. The First Need’s charcoal canister is not big
enough to be effective against poisonous chemicals — you need a pound of
charcoal for this — so it just adds unnecessary weight, and provides a
potential haven for the growth of harmful bacteria. If you own a First Need
filter, flush it with iodine after each trip.
The Katadyn(R) water filter is expensive (over $200), but is completely
effective against bacteria as well as giardia. Moreover, it can be cleaned
after it clogs up. The Katadyn is effective at removing smaller bacteria
such as E. coli. However, its .2 micron filter is not effective against
any virus. If you travel abroad (to Nepal for example), you risk viral
infections such as Hepatitis A and Hepatitis non-A non-B, among others.
MSR has a new water filter, which may be superior to the Katadyn. Results
from the field aren’t in yet.
To be entirely safe, water should be boiled for at least five minutes.
Giardia is killed in less than a minute at 176 degrees, well under the
boiling point. Bacteria and viruses last somewhat longer, but are probably
killed in less than five minutes at 190 degrees. Some viruses may last
longer; nobody knows. At 10,000 feet water boils at 194 degrees; above
this altitude boil water about an extra minute for each 1000 feet.
If you have neither the time nor the inclination to boil water, iodine
is equally effective. After 15 minutes (30 minutes for very cold water),
a sufficient dose of iodine kills all protozoa, bacteria, and viruses.
One readily-available choice is Potable-Aqua(R) tablets. Dissolve one
tablet per liter of water (two tablets if cloudy) and wait. The problem
with iodine tablets is that they degrade upon contact with moisture, so
keep that bottle dry, and discard it upon returning home.
Avoid halazone and Clorox, because chlorine is volatile, slow to disinfect,
and works differently against protozoa and viruses at various pH levels.
It also reacts with organic compounds to form carcinogenic chloramines.
Iodine is not highly toxic, and in fact is an essential ingredient of
human nutrition. However, continuous ingestion of large doses may cause
health problems, so don’t iodinate all your water for more than a few
months at a time.
The accepted concentration for iodine disinfection is 8 milligrams per
liter, but this is mostly to get rid of protozoan parasites. A good way
to reduce overall iodine consumption and minimize that iodine flavor is
to filter first, then use a low concentration of iodine to get rid of
bacteria and viruses. For this, a concentration of .5 mg/L is deemed
adequate, so one capful of PolarPure or one Potable-Aqua tablet should
disinfect around 16 liters of lightly filtered water. The Timberline(R)
filter, with its 2 micron pores, is fine for removing protozoa.
Giardia has become a well-known, almost fashionable, outdoor hazard.
Many people who experience gastro-intestinal problems after drinking
bad water think they have contracted giardia. In many cases they have
contracted something else. Since the only FDA-approved treatment for
giardia (Flagyl) is very nasty, it’s wise to make sure you really have
giardia before taking Flagyl. Most low-grade bacterial infections go away
on their own, and Flagyl is ineffective against viral infections. One
alternative to Flagyl is quinacrine. In many parts of the world (Asia
for example) Tinidazole is available, and is preferable to Flagyl because
it is less toxic and quicker acting.
[This information based on “Medicine for Mountaineering”, various owner’s
pamphlets, and personal experience.]
A packet of information arrived recently from Recovery Engineering
in Minneapolis, which I’ll summarize as promised.
They have a new product, the Pur Scout, which I believe is destined
to replace the First Need as the most popular low-cost filter. It
has the same 1 micron filter plus iodine matrix as the Pur Explorer,
pumps a quart in 120 seconds, but weighs only 12 oz! Capacity is
200 gallons, twice the First Need, but its $60 cost is less than
twice as much. The Scout is not self-cleaning like the Explorer,
and is only half the speed, with 2/5 the filter life.
Unlike other water filters, all Pur products meet EPA’s purification
guidelines. No other filter does this, because no other filter can
remove viruses. Here is the abstract from a study done at U Arizona
on the Pur Tritek(tm) system:
“Three identical [Pur Traveller water filters] were evaluated
for their ability to inactivate/remove Klebsiella terrigena,
poliovirus type1, rotavirus SA-11, and Giardia lamblia cysts.
The units were operated according to the manufacturer’s
instructions until the designed lifetime of 100 gallons (378
liters) passed through. The units were challenged with [the
micro-organisms mentioned above] after a passage of 0, 50, 75
and 100 gallons. At the 75% lifetime challenge, ‘worst case’
water quality of 1500 mg/l dissolved solids, 10 mg/l organic
matter, 4 degrees C, with a turbidity of 30 NTU and a pH of 9
was used. For the 100% lifetime test the worst case water
quality at pH 5 was used. The units were also tested after
stagnation for 48 hours at the 50%, 75%, and 100% [stages].
“At 0 and 50% lifetime test points, > 99.9999% of the bacteria,
> 99.9% of the Giardia cysts, and > 99.99% of the test viruses
were removed. With worst case water two passages of the test
water through the units was required to achieve these same
removals. These units would comply with criteria guidelines
suggested by the US EPA…
“One passage of the pH 9 worst case water was not sufficient
to remove the Klebsiella terrigena and poliovirus type1 to
the required reduction. However, the required reduction [was]
achieved by passage of the test water through the units a
second time… Holding the water for 5 to 10 minutes after
it had passed through the units also resulted in a further
reduction of test bacteria and viruses.”
What is Klebsiella terrigena anyway? I assume it’s a bacteria, but
what disease does it cause? And what does NTU stand for? Also, is
parts per million (ppm) the same as milligrams per liter (mg/l)?
Here is the residual iodine in ppm after treatment:
cup1 cup2 cup3
0% .7 .7 .7
50% .6 .5 .6
75% .6 .6 .7
100% .7 .6 .8
This indicates that the filter still had plenty of life at 100 gallons.
It also indicates that there is enough residual iodine to kill off all
viruses and bacteria overnight (assuming ppm = mg/l). At these levels
some iodine taste may be present, which can be removed with the optional
charcoal filter. Since the charcoal filter also removes iodine, it
would be prudent to use it only when filtering good quality water above
5 degrees C. It’s a tradeoff, though: when travelling thru agricultural
areas, charcoal filtration helps remove pesticides and herbicides.
All in all, I’ve decided to trade in my Katadyn for a Pur Explorer. I
used an MSR last week on the Rogue, and liked its pump action and bottle
attachment, but it *did* start to clog. Anybody want to buy my Katadyn
(in excellent condition) for a mere $185? F*ck the Swiss.
OCR’ed memo from the Center from Disease Control:
GIARDIASIS: By Dennis D. Juranek, Chief, Epidemiology Activity
Parasitic Diseases Branch
Division of Parasitic Diseases
Centers for Disease Control
Transmission and Control
During the past fifteen years giardiasis has been recognized as one of the
most frequently occurring waterborne diseases in the United States (1).
Giardia lamblia have been discovered in the United States in places as far
apart as Estes Park, Colorado (near the Continental Divide); Missoula,
Montana; Wilkes-Barre, Scranton, and Hazleton, Pennsylvania; and Pittsfield
and Lawrence, Massachusetts just to name a few. In light of recent large
outbreaks of waterborne giardiasis, it seem timely to present reliable
information on the way in which giardiasis is acquired, treated, and
Giardiasis: Prevalence and Symptoms
Giardiasis is a disease caused by a one-celled parasite with the scientific
name Giardia lamblia. The disease is characterized by intestinal symptoms
that usually last one week or more and may be accompanied by one or more of
the following: diarrhea, abdominal cramps, bloating, flatulence, fatigue, and
weight loss (see Table 1). Although vomiting and fever are listed in Table 1
as relatively frequent symptoms, they have been uncommonly reported by people
involved in waterborne outbreaks of giardiasis in the United States. Table 1
also suggests that 13 percent of patients with giardiasis may have blood in
their stool. Giardia, however, rarely causes intestinal bleeding. Therefore,
blood in the stool of a patient with giardiasis almost always indicates the
presence of a second disease.
While most Giardia infections persist only for one or two months, some people
undergo a more chronic phase, which can follow the acute phase or may become
manifest without an antecedent acute illness. The chronic phase is
characterized by loose stools, and increased abdominal gassiness with
cramping, flatulence and burping. Fever is not common, but malaise, fatigue,
and depression may ensue (2). For a small number of people, the persistence of
infection is associated with the development of marked malabsorption and
weight loss (3). Similarly, lactose (milk) intolerance can be a problem for
some people. This can develop coincidentally with the infection or be
aggravated by it, causing an increase in intestinal symptoms after ingestion
of milk products.
Some people may have several of these symptoms without evidence of diarrhea or
have only sporadic episodes of diarrhea every 3 or 4 days. Still others may
not have any symptoms at all. Therefore, the problem may not be whether you
are infected with the parasite or not, but how harmoniously you both can live
together, or how to get rid of the parasite (either spontaneously or by
treatment) when the harmony does not exist or is lost.
Three drugs are available in the United States to treat giardiasis: quinacrine
(Atabrine*), metronidazole (Flagyl*), and furazolidone (Furoxone*). All are
prescription drugs. In a recent review of drug trials in which the efficacies
of these drugs were compared, quinacrine produced a cure in 93% of 129
patients, metronidazole cured 92% of 219, and furazolidone cured 84% of 150
patients (4). Quinacrine is generally the least expensive of the anti-Giardia
medications but it often causes vomiting in children younger than 5 years
old. Although the treatment of giardiasis is not an FDA-approved indication
for metronidazole, the drug is commonly used for this purpose. Furazolidone
is the least effective of the three drugs, but is the only anti-Giardia
medication that comes as a liquid preparation, which makes it easier to
deliver the exact dose to small children and makes it the most convenient
dosage form for children who have difficulty taking pills. Cases of chronic
giardiasis refractory to repeated courses of therapy have been noted, one of
which responded to combined quinacrine and metronidazole treatment (5).
(*) Use of trade names is for purposes of identification only.
Etiology and Epidemiology
Giardiasis occurs worldwide. In the United States, Giardia is the parasite
most commonly identified in stool specimens submitted to state laboratories
for parasitologic examination. From 1977 through 1979, approximately 4% of 1
million stool specimens submitted to state laboratories were positive for
Giardia (6). Other surveys have demonstrated Giardia prevalence rates ranging
from 1 to 20% depending on the location and ages of persons studied.
Giardiasis ranks among the top 20 infectious diseases that cause the greatest
morbidity in Africa, Asia, and Latin America (7); it has been estimated that
about 2 million infections occur per year in these regions (8).
People who are at highest risk for acquiring a Giardia infection in the United
States may be placed into five major categories:
1) People in cities whose drinking water originates from streams or
rivers and whose water treatment process does not include
filtration, or filtration is ineffective because of malfunctioning
3) International travelers
4) Children who attend day-care centers, day-care center staff, and
parents and siblings of children infected in day-care centers.
5) Homosexual men.
People in categories 1, 2, and 3 have in common the same general source of
infections, i.e., they acquire Giardia from fecally contaminated drinking
water. The city resident usually becomes infected because the municipal water
treatment process does not include a filter that is necessary to physically
remove the parasite from the water. The number of people in the United States
at risk (i.e., the number who receive municipal drinking water from unfiltered
surface water) is estimated to be 20 million. International travelers may
also acquire the parasite from improperly treated municipal waters in cities
or villages in other parts of the world, particularly in developing
countries. In Eurasia, only travelers to Leningrad appear to be at increased
risk. In prospective studies, 88% of U.S. and 35% of Finnish travelers to
Leningrad who had negative stool tests for Giardia on departure to the Soviet
Union developed symptoms of giardiasis and had positive tests for Giardia
after they returned home (10,11). With the exception of visitors to Leningrad,
however, Giardia has not been implicated as a major cause of traveler’s
diarrhea. The parasite has been detected in fewer than 2% of travelers who
develop diarrhea. Hikers and campers risk infection every time they drink
untreated raw water from a stream or river.
Persons in categories 4 and 5 become exposed through more direct contact with
feces of an infected person, e.g., exposure to soiled diapers of an infected
child (day-care center-associated cases), or through direct or indirect
anal-oral sexual practices in the case of homosexual men.
Although community waterborne outbreaks of giardiasis have received the
greatest publicity in the United States during the past decade, about half of
the Giardia cases discussed with staff of the Centers for Disease Control in
the past 2 to 3 years have a day-care center exposure as the most likely
source of infection. Numerous outbreaks of Giardia in day-care centers have
been reported in recent years. Infection rates for children in day-care
center outbreaks range from 21 to 44% in the United states and from 8 to 27%
in Canada (12,13,14,15,16,17). The highest infection rates are usually
observed in children who wear diapers (l to 3 years of age). In one study of
18 randomly selected day care centers in Atlanta (CDC unpublished data), 10%
of diapered children were found infected. Transmission from this age group to
older children, day-care staff, and household contacts is also common. About
20% of parents caring for an infected child will come infected.
It is important that local health officials and managers of water utility
companies realize that sources of Giardia infection other than municipal
drinking water exist. Armed with this knowledge, they are less likely to make
a quick (and sometimes wrong) assumption that a cluster of recently diagnosed
cases in a city is related to municipal drinking water. Of course, drinking
water must not be ruled out as a source of infection when a larger than
expected number of cases are recognized in a community, but the possibility
that the cases are associated with a day-care center outbreak, drinking
untreated stream water, or international travel should also be
To understand the finer aspects of Giardia transmission and the strategies for
control, one must become familiar with several aspects of the parasite’s
biology. Two forms of the parasite exist: a trophozoite and a cyst, both of
which are much larger than bacteria (see Figure 1). Trophozoites live in the
upper small intestine where they attach to the intestinal wall by means of a
disc-shaped suction pad on their ventral surface. Trophozoites actively feed
and reproduce at this location. At some time during the trophozoite’s life,
it releases its hold on the bowel wall and floats in the fecal stream through
the intestine. As it makes this journey, it undergoes a morphologic
transformation into an egglike structure called a cyst. The cyst, which is
about 6 to 9 micrometers in diameter x 8 to 12 micrometers (1/100 millimeter)
in length, has a thick exterior wall that protects the parasite against the
harsh elements that it will encounter outside the body. This cyst form of the
parasite is infectious for other people or animals. Most people become
infected either directly by hand-to-mouth transfer of cysts from the feces of
an infected individual, or indirectly by drinking feces-contaminated water.
Less common modes of transmission included ingestion of fecally contaminated
food and hand-to-mouth transfer of cysts after touching a fecally contaminated
surface. After the cyst is swallowed, the trophozoite is liberated through
the action of stomach acid and digestive enzymes and becomes established in
the small intestine.
Although infection after the ingestion of only one Giardia cyst is
theoretically possible, the minimum number of cysts shown to infect a human
under experimental conditions is ten (18). Trophozoites divide by binary
fission about every 12 hours. What this means in practical terms that if a
person swallowed only a single cyst, reproduction at this rate would result in
more than 1 million parasites 10 days later, and 1 billion parasites by day 15.
The exact mechanism by which Giardia causes illness is not yet well
understood, but is not necessarily related to the number of organisms
present. Nearly all of the symptoms, however, are related to dysfunction of
the gastrointestinal tract. The parasite rarely invades other parts of the
body, such as the gall bladder or pancreatic ducts. Intestinal infection does
not result in permanent damage.
Data reported to the CDC indicate that Giardia is the most frequently
identified cause of diarrheal outbreaks associated with drinking water in the
United States. The remainder of this article will be devoted to waterborne
transmission of Giardia. Waterborne epidemics of giardiasis are a relatively
frequent occurrence. In 1983, for example, Giardia was identified as the
cause of diarrhea in 68% of waterborne outbreaks in which the causal agent was
identified (19). From 1965 to 1982, more than 50 waterborne outbreaks were
reported (20). In 1984, about 250,000 people in Pennsylvania were advised to
boil drinking water for 6 months because of Giardia-contaminated water.
Many of the municipal waterborne outbreaks of Giardia have been subjected to
intense study to determine their cause. Several general conclusions can be
made from data obtained in those studies. Waterborne transmission of Giardia
in the United States usually occurs in mountainous regions where community
drinking water is obtained from clear running streams, is chlorinated but is
not filtered before distribution. Although mountain streams appear to be
clean, fecal contamination upstream by human residents or visitors, as well as
by Giardia-infected animals such as beavers, has been well documented. It is
worth emphasizing that water obtained from deep wells is an unlikely source of
Giardia because of the natural filtration of water as it percolates through
the soil to reach underground cisterns. Well-water sources that pose the
greatest risk of fecal contamination are those that are poorly constructed or
improperly located. A few outbreaks have occurred in towns that included
filtration in the water treatment process, but the filtration was not
effective in removing Giardia cysts because of defects in filter construction,
poor maintenance of the filter media, or inadequate pretreatment of the water
before it was filtered. Occasional outbreaks have also occurred because of
accidental cross-connections between water and sewerage systems.
One can conclude from these data that two major ingredients are necessary for
waterborne outbreak. First, there must be Giardia cysts in untreated source
water and, second, the water purification process must either fail to kill or
fail to remove Giardia cysts from the water.
Although beavers are often blamed for contaminating water with Giardia cysts,
it seems unlikely that they are responsible for introducing the parasite into
new areas. It is far more likely that they are also victims: Giardia cysts
may be carried in untreated human sewage discharged into the water by
small-town sewage disposal plants or originate from cabin toilets that drain
directly into streams and rivers. Backpackers, campers, and sports
enthusiasts may also deposit Giardia-contaminated feces in the environment
that are subsequently washed into streams by rain. In support of this concept
is a growing amount of data that indicate a higher Giardia infection rate in
beavers living downstream from U.S. National Forest campgrounds compared with
a near zero rate of infection in beavers living in more remote areas.
Although beavers may be unwitting victims in the Giardia story, they still
play an important part in the transmission scheme, because they can (and
probably do) serve as amplifying hosts. An amplifying host is one that is
easy to infect, serves as a good habitat for the parasite to reproduce, and,
in the case of Giardia, returns millions of cysts to the water for every one
ingested. Beavers are especially important in this regard because they tend
to defecate in or very near the water, which ensures that most of the Giardia
cysts excreted are returned to the water
The contribution of other animals to waterborne outbreaks of Giardia is less
clear. Muskrats (another semiaquatic animal) have been found in several parts
of the United States to have high infection rates (30 to 40%) (2l). Recent
studies have shown that muskrats can be infected with Giardia cysts obtained
from humans and beavers. Occasional Giardia infections have been reported in
coyotes, deer, elk, cattle, dogs, and cats, but not in horses and sheep,
encountered in mountainous regions of the United States. Naturally occurring
Giardia infections have not been found in most other wild animals (bear,
nutria, rabbit, squirrel, badger, marmot, skunk, ferret, porcupine, mink,
raccoon, river otter, bobcat, lynx, moose, bighorn sheep) (22).
Removal from Municipal Water Supplies
During the past 10 years, scientific knowledge about what is required to kill
or remove Giardia cysts from a contaminated water supply has increased
considerably. For example, it is known that cysts can survive in cold water
(4 deg C) for at least 2 months and that they are killed instantaneously by
boiling water (100 deg C) (23,24). It is not known how long the cysts
will remain viable at other water temperatures (e.g., at 0 deg C or in a
canteen at 15-20 deg C), nor is it known how long the parasite will survive
on various environment surfaces, e.g., under a pine tree, in the sun,
on a diaper-changing table, or in carpets in a day-care center.
The effect of chemical disinfection, such as chlorine, on the viability of
Giardia cysts is an even more complex issue. It is clear from the number of
waterborne outbreaks of Giardia that have occurred in communities where
chlorine was employed as a disinfectant that the amount of chlorine used
routinely for municipal water treatment is not effective against Giardia
cysts. These observations have been confirmed in the laboratory under
experimental conditions (25,26,27). This does not mean, however, that chlorine
does not work at all. It does work under certain favorable conditions.
Without getting too technical, one can gain some appreciation of the problem
by understanding a few of the variables that influence the efficacy of
chlorine as a disinfectant.
1) Water pH: at pH values above 7.5, the disinfectant capability of
chlorine is greatly reduced.
2) Water temperature: the warmer the water, the higher the efficacy.
Thus, chlorine does not work well in ice-cold water from mountain
3) Organic content of the water: mud, decayed vegetation, or other
suspended organic debris in water chemically combines with chlorine
making it unavailable as a disinfectant.
4) Chlorine contact time: the longer Giardia cysts are exposed to
chlorine, the more likely it is that the chemical will kill them.
5) Chlorine concentration: the higher the chlorine concentration, the
more likely chlorine will kill Giardia cysts. Most water treatment
facilities try to add enough chlorine to give a free (unbound)
chlorine residual at the customer tap of 0.5 mg per liter of water.
The five variables above are so closely interrelated that an unfavorable
occurrence in one can often be compensated for by improving another. For
example, if chlorine efficacy is expected to be low because water is obtained
from an icy stream, either the chlorine contact time or chlorine
concentration, or both could be increased. In the case of
Giardia-contaminated water, it might be possible to produce safe drinking
water with a chlorine concentration of 1 mg per liter and a contact time as
short as 10 minutes if all the other variables were optimal (i.e., pH of 7.0,
water temperature of 25 deg C, and a total organic content of the water close to
zero). On the other hand, if all of these variables were unfavorable (i.e.,
pH of 7.9, water temperature of 5 deg C, and high organic content), chlorine
concentrations in excess of 8 mg per liter with several hours of contact time
may not be consistently effective. Because water conditions and water
treatment plant operations (especially those related to water retention time
and, therefore, to chlorine contact time) vary considerably in different parts
of the United States, neither the U.S. Environmental Protection Agency nor the
CDC has been able to identify a chlorine concentration that would be safe yet
effective against Giardia cysts under all water conditions. Therefore, the
use of chlorine as a preventive measure against waterborne giardiasis
generally has been used under outbreak conditions when the amount of chlorine
and contact time have been tailored to fit specific water conditions and the
existing operational design of the water utility.
In an outbreak, for example, the local health department and water utility may
issue an advisory to boil water, may increase the chlorine residual at the
consumer’s tap from 0.5 mg per liter to 1 or 2 mg per liter, and, if the
physical layout and operation of the water treatment facility permit, increase
the chlorine contact time. These are emergency procedures intended to reduce
the risk of transmission until a filtration device can be installed or
repaired or until an alternative source of safe water, such as a well, can be
The long-term solution to the problem of municipal waterborne outbreaks of
giardiasis will involve improvements in and more widespread use of filters in
the municipal water treatment process. The sand filters most commonly used in
municipal water treatment today cost millions of dollars to install, which
makes them unattractive for many small communities. Moreover, the pore sizes
in these filters are not sufficiently small to remove a Giardia (6 to 9
micrometers x 8 to 12 micrometers). For the sand filter to remove Giardia
cysts from the water effectively, the water must receive some additional
treatment before it reaches the filter. In addition, the flow of water
through the filter bed must be carefully regulated.
An ideal prefilter treatment for muddy water would include sedimentation (a
holding pond where the large suspended particles are allowed to settle out by
the action of gravity) followed by flocculation or coagulation (the addition
of chemicals such as alum or ammonium to cause microscopic particles to clump
together). The large particles resulting from the flocculation/coagulation
process, including Giardia cysts bound to other microparticulates, are easily
removed by the sand filter. Chlorine is then added to kill the bacteria and
viruses that may escape the filtration process. If the water comes from a
relatively clear source, chlorine may be added to the water before it reaches
the filter. The point here is that successful operation of a complete water
treatment facility is a complex process that requires considerable training.
Troubleshooting breakdowns or recognizing potential problems in the system
before they occur often requires the skills of an engineer. Unfortunately,
most small water utilities that have a water treatment facility that includes
filtration cannot afford the services of a full-time engineer. Filter
operation or maintenance problems in such systems may not be detected until a
Giardia outbreak is recognized in the community. The bottom line is that
although, in reference to municipal systems, water filtration is the best that
water treatment technology has to offer against waterborne giardiasis, it is
not infallible. For municipal water filtration facilities to work properly,
they must be properly constructed, operated, and maintained.
Water Disinfection in the Out-of-Doors
Whenever possible, persons in the out-of-doors should carry drinking water of
known purity with them. When this is not practical, and water from streams,
lakes, ponds, and other outdoor sources must be used, time should be taken to
disinfect the water before drinking it.
Boiling water is one of the simplest and most effective ways to purify water.
Boiling for 1 minute is adequate to kill Giardia as well as most other
bacterial or viral pathogens likely to be acquired from drinking polluted
Disinfection of water with chlorine or iodine is considered less reliable than
boiling for killing Giardia. However, it is recognized that boiling drinking
water is not practical under many circumstances. Therefore, when one cannot
boil drinking water, chemical disinfectants such as iodine or chlorine should
be used. This will provide some protection against Giardia and will destroy
most bacteria and viruses that cause illness. Iodine or chlorine concentrations
of 8 mg/liter (8ppm) with a minimum contact time of 30 minutes are recommended.
If the water is cold (less than 10 deg C or 5O deg F) we suggest a minimum
contact time of 60 minutes. If you have a choice of disinfectants, use iodine.
Iodine’s disinfectant activity is less likely to be reduced by unfavorable
water conditions, such as dissolved organic material in water or by water with
a high pH, than chlorine.
Below are instructions for disinfecting water using household tincture of
iodine or chlorine bleach. If water is visibly dirty, it should first be
strained through a clean cloth into a container to remove any sediment or
floating matter. Then the water should be treated with chemicals as follows:
Tincture of iodine from the medicine chest or first aid kit can be used to
treat water. Mix thoroughly by stirring or shaking water in container and let
stand for 30 minutes.
Tincture of Iodine Drops* to be Added per Quart or Liter
Clear Water Cold or Cloudy Water**
2% 5 10
* 1 drop = 0.05ml
** Very turbid or very cold water may require prolonged contact time; let
stand up to several hours or even overnight.
Liquid chlorine bleach used for washing clothes usually has 4% to 6% available
chlorine. The label should be read to find the percentage of chlorine in the
solution and the treatment schedule below should be followed.
Drops* to be Added per Quart or Liter
Available Chlorine Clear Water Cold or Cloudy Water**
1% 10 20
4% to 6% 2 4
7% to lO% 1 2
Unknown 10 20
* 1 drop = 0.05ml
** Very turbid or very cold water may require prolonged contact time; let
stand up to several hours or even overnight.
Mix thoroughly by stirring or shaking water in container and let stand for 30
minutes. A slight chlorine odor should be detectable in the water; if not,
repeat the dosage and let stand for an additional 15 minutes before using.
Newcomers in the battle against waterborne giardiasis include a variety
of portable filters for field or individual use as well as some household
filters. Manufacturers’ data accompanying these filters indicate that some
can remove particles the size of a Giardia cyst or smaller and may be capable
of providing a source of safe drinking water for an individual or family
during a waterborne outbreak. Such devices, if carefully selected, might also
be useful in preventing giardiasis in international travelers, backpackers,
campers, sportsmen, or persons who live or work in areas where water is known
to be contaminated.
Unfortunately, there are yet few published reports in the scientific
literature detailing both the methods used and the results of tests employed
to evaluate the efficacy of these filters against Giardia. Until more
published experimental data become available, there are a few common sense
things that a consumer should look for when selecting a portable or household
filter. The first thing to consider is the filter media. Filters relying
solely on ordinary or silver-impregnated carbon or charcoal should be avoided,
because they are not intended to prevent, destroy, or repel micro-organisms.
Their principal use is to remove undesirable chemicals, odors, and very large
particles such as rust or dirt.
Some filters rely on chemicals such as iodide-impregnated resins to kill
Giardia. While properly designed and manufactured iodide-impregnated resin
filters have been shown to kill many species of bacteria and virus present in
human feces, their efficacy against Giardia cysts is less well-established.
The principle under which these filters operate is similar to that achieved by
adding the chemical disinfectant iodine to water, except that the
micro-organisms in the water pass over the iodide-impregnated disinfectant as
the water flows through the filter.
While the disinfectant activity of iodide is not as readily affected as
chlorine by water pH or organic content, iodide disinfectant activity is
markedly reduced by cold water temperatures. Experiments on Giardia indicate
that many of the cysts in cold water (4 deg C) remain viable after passage
through filters containing tri-iodide or penta-iodide disinfectants (28). As
indicated earlier, longer contact times (compared to those required to kill
bacteria) are required when using chemical filters to process cold water for
Giardia protection. Presently available chemical filters also are not
recommended for muddy or very turbid water. Additionally, filters relying
solely on chemical action usually give no indication to the user when
disinfectant activity has been depleted.
The so-called microstrainer types of filters are true filters. Manufacturer
data accompanying these filters indicate that some have a sufficiently small
pore size to physically restrict the passage of some micro-organisms through
the filter. The types of filter media employed in microstraining filters
include orlon, ceramic, and proprietary materials. Theoretically, a filter
having an absolute pore size of less than 6 micrometers might be able to
prevent Giardia cysts of 8 to 10 micrometers in diameter from passing.
However, when used as a water sampling device during community outbreaks,
portable filters in the 1- to 3- micrometer range more effectively removed
Giardia cysts from raw water than filters with larger pore sizes. For
effective removal of bacterial or viral organisms which cause disease in
humans, microstraining filters with pore sizes of less than 1 micrometer are
advisable. However, the smaller the pores, the more quickly the filters will
tend to clog. To obtain maximum filter life, and as a matter of reasonable
precaution, the cleanest available water source should always be used. Keep
in mind, however, that even sparkling, clear mountain streams can be heavily
Secondly, because infectious organisms can be concentrated on the filter
element/media, it is important to consider whether the filter element can be
cleaned or replaced without posing a significant health hazard to the user.
Properly engineered portable filters should also minimize the possibility of
contaminating the “clean water side” of the filter with contaminated water
during replacement or cleaning of the filter element. This is especially
important for filters used in the field where they are often rinsed or
“cleaned” in a stream or river that may be contaminated.
Ongerth (29) recently evaluated four filters (First Need, H20K, Katadyn, the
Pockett Purifier) for their ability to remove Giardia cysts from water. Only
the First Need and Katadyn filters removed 100% of the cysts.
In conclusion, during the past fifteen years, giardiasis has been recognized
as one of the most frequently occurring waterborne diseases in the United
States. The most common sources of water contamination include improperly
treated municipal sewage, infected animals, and indiscriminate defecation by
outdoorsmen. Chlorine concentrations in the 0.1 mg per liter to 0.5 mg per
liter range are largely ineffective against Giardia at the contact times
commonly employed by municipal water utilities. The long-term solution to the
problem of municipal waterborne outbreaks of giardiasis will involve
appropriate pretreatment combined with improvements in and more widespread use
of filters in the municipal water treatment process. While both micrometer-
and submicrometer-rated filters are being employed on a limited scale for
personal or household use, further evaluation of the efficacy of filters
distributed by different manufacturers is needed to enable individuals and
public health personnel to distinguish those that are safe and effective from
those that are not.
Diarrhea* 84 516
Malaise 80 56
Weakness 72 324
Abdominal cramps 63 412
Weight loss (O.5 – 11 kg) 63 412
Greasy, foul smelling stools 59 412
Nausea 57 444
Headaches 53 92
Anorexia 49 156
Abdominal bloating 45 380
Flatulence 41 388
Constipation 25 88
Vomiting 24 488
Fever 22 32
Abdomen tender to palpitation 66 92
Anemia 15 124
Leukocytosis 9 32
Increased mucus 56 32
Increased neutral fats 50 32
Blood 13 156
* Index symptom; may be biased (upward)
TABLE 1 – Based on data from Fifty diseases: Fifty Diagnoses, by M.G. Periroth
and D.J. Weiland.
Year Book Medical Publishers, Inc., Chicago, 1981, pp. 158-159. Reprinted by
special arrangement with Year Book Publishers, Inc.
1. Craun, Gunther T. Waterborne Giardiasis in the United States: A review.
American Journal of Public Health 69:817-819, 1979.
2. Weller, Peter F. Intestinal Protozoa: Giardiasis. Scientific American
3. Id. 2.
4. Davidson, R.A. Issues in Clinical Parasitology: The treatment of Giardiasis.
Am J. Gastroenterol. 79:256-261, 2984
5. Id. 2.
6. Intestinal Parasite Surveillance, Annual Summary 1978, Atlanta, Centers for
Disease Control, 1979.
7. Walsh, J.D. Warren K. s. Selective Primary Health Care: An Interim Strategy
for Disease Control in developing countries. N. Engl. J. Med., 301:967-974,
8. Walsh, J.A. Estimating the Burden of Illness in the Tropics, In Tropical and
Geographic Medicine, Edited by K.S. Warren and A.F. Mahmoud, McGraw-Hill,
New York, 1981, pp 1073-1085.
9. Weniger, B.D., Blaser, MlJ., Gedrose, J., Lippy, E.C., Juranek, D.D. an
Outbreak of Waterborne Giardiasis Associated with Heavy Water Runoff due to
Warm Weather and Volcanic Ashfall. Am. J. Public Health 78:868-872, 1983.
10. Brodsky, R.E., Spencer, H.C., Schultz, M.G. Giardiasis in American
Travelers to the Soviet Union. J. Infect Dis. 130:319-323, 1974.
11. Jokipii, L., Jokipii, A.M.M. Giardiasis in Travelers: A prospective Study.
J. Infect. Dis., 130:295-299, 1974.
12. Black, R.E., Dykes, A.C., Anderson, K.E., Wells, J.G., Sinclair, S.P.,
Gary, G.W., Hatch, M.H., Gnagarosa, E.J. Handwashing to Prevent Diarrhea in
Day-Care Centers. Am. J. Epidemiol. 113:445-451, 1981.
13. Pickering, L.K., Woodward, W.E., DuPont, H. L., Sullivan, P. Occurrence of
Giardia lamblia in Children in Day Care Centers. J. Pediatr. 104:522-526,
14. Sealy, D.P., Schuman, S.H. Endemic Giardiasis and Day Care. Pediatrics
15. Pickering, L.K., Evans, D.G., DuPont, H.L., Vollet, J.J., III, Evans, D.J.,
Jr. diarrhea Caused by Shigella, Rotavirus, and Giardia in Day-care
Centers: Prospective Study. J. Peidatr., 99:51-56, 1981.
16. Keystone, J.S., Yang, J., Grisdale, D., Harrington, M., Pillow, L.,
Andreychuk, R. Intestinal Parasites in Metropolitan Toronto Day-Care
Centres. Can J. Assoc. J. 131:733-735, 1984.
17. Keystone, J.S., Kraden, S., Warren, M.R. Person-to-Person Transmission of
Giardia lamblia in Day-Care Nurseries. Can. Med. Assoc. J. 119:241-242,
18. Rendtorff, R.C. The Experimental Transmission of Human Intestinal Protozoan
Parasites. II. Giardia lamblia cysts Given In Capsules, Am. J. Hygiene
19. Water-related Disease Outbreaks Surveillance, Annual Summary 1983. Atlanta,
Centers for Disease Control, 1984.
20. Craun, G.F. Waterborne Outbreaks of Giardiasis–Current Status in Giardia
and Giardiasis, edited by S.L. Erlandsen and E.A Meyer. Pleunu Press. New
York, 1984, pp 243-261.
21. Frost, F. Plan, B., Liechty, B. Giardia Prevalence in Commercially Trapped
Mammals. J. Environ. Health 42:245-249.
22. Id. 21.
23. Id. 18.
24. Bingham, A.K., Jarroll, E.L., Meyer, E.A. Radulescu, S. Introduction of
Giardia Excystation and the effect of Temperature on cyst Viability
compared by Eosin-Exclusion and In Vitro Excystation in Waterborne
Transmission of Giardiasis. Edited by J. Jakubowski and H. C. Hoff, U.S.
Environmental Protection Agency, Washington, DC, 1979, pp. 217-229.
25. Jarroll, E.L., Bingham, A.K., Meyer, E.A. Effect of Chlorine on Giardia
lamblia Cyst Viability. Appl. Environ. Microbiol. 41:483-487, 1981.
26. Jarroll, E.L., Jr., Bingham, A.K. Meyer, E.A. Inability of an Iodination
Method to Destroy completely Giardia Cysts in Cold Water. West J. Med.
27. Jarroll, E.L., Jr., Bingham, A.K., Meyer, E.A. Giardia Cyst Destruction:
Effectiveness of Six Small-Quantity Water Disinfection Methods. Am. J.
Trop. Med. Hygiene 29:8-11, 1980.
28. Marchin, B.L., Fina, L.R., Lambert, J.L., Fina, G.T. Effect of resin
disinfectants–13 and –15 on Giardia muris and giardia lamblia. Appl
Environ. Microbiol. 46:965-9, 1983.
29. Ongerth JE, Johnson RL, Macdonald SC, Frost F, Stibbs HH. Back-country
water treatment to prevent giardiasis. Am J Public Health
Back-country water treatment to prevent giardiasis.
Jerry E. Ongerth, PhD, PE, Ron L. Johnson, Steven C Macdonald, MPH, Floyd Frost,
PhD, and Henry H. Stibbs, PhD
American Journal of Public Health December 1989, Vol 79, No 12, pp 1633-1637.
Copyright 1989 AJPH 0090-0036/89$1.50 [used without permission]
This study was conducted to provide current information on the effectiveness of
water treatment chemicals and filters for control of Giardia cysts in areas
where treated water is not available. Four filters and seven chemical
treatments were evaluated for both clear and turbid water at 10C. Three contact
disinfection devices were also tested for cyst inactivation. Filters were
tested with 1-liter volumes of water seeded with 3×10^4 cysts of G. lamblia
produced in gerbils inoculated with in vitro cultured trophozoites; the entire
volume of filtrate was examined for cyst passage. Chemical treatments were
evaluated at concentrations specified by the manufacturer and for contact times
that might be expected of hikers (30 minutes) and campers (eight hours, i.e.,
overnight). Two of the four filter devices tested were 100 percent effective
for Giardia cyst removal. Of the other two filters, one was 90 percent
effective and the other considerably less effective. Among the seven
disinfection treatments, the iodine-based chemicals were all significantly more
effective than the chlorine-based chemicals. None of the chemical treatments
achieved 99.9 percent cyst inactivation with only 30-minute contact. After an
eight-hour contact each of the iodine but none of the chlorine preparations
achieved at least 99.9 percent cyst inactivation. None of the contact
disinfection devices provided appreciable cyst inactivation. Heating water to
at least 70C for 10 minutes was an acceptable alternative treatment.
Giardia lamblia is the most commonly identified human intestinal parasite in the
United States. Giardiasis is commonly transmitted between humans, especially
among small children. lt is also transmitted in water, particularly in the
mountainous regions of the U.S. Since 1965, over 80 waterborne outbreaks of
giardiasis have occurred in community water systems, affecting more than 20,000
persons (1). Giardiasis in hikers and campers has also been documented (2,3);
indeed, it is commonly considered a backpackers’ illness. Giardia cysts in
concentrations as high as four per gallon have been detected in untreated
surface water in northeastern and western states (4).
Concern over waterborne transmission of Giardia has led to development of a
variety of chemical disinfectants and portable filters for individual use in the
backcountry. Although some information on such methods has been reported
(2,5,6), there is no comprehensive guide to their reliability in actually
removing or inactivating Giardia cysts. We tested four commercially available
portable filters and one contact disinfection device for their ability to remove
Giardia cysts from water. We also evaluated the cysticidal effectiveness of
seven chemical disinfectants and three contact disinfection devices.
Cysts of G. lamblia were prepared for use in both the filtration and
disinfection tests by propagation in gerbils inoculated with trophozoites from
sterile culture. Trophozoites were of two isolates: one from a beaver (Be-4
isolate from Alberta) and one from a human (H-2 CSU isolate from Colorado).
Cysts were concentrated from crushed, filtered gerbil feces by flotation on zinc
sulfate (sp. gr. 1.18), cleaned, and stored in distilled water at 4C for up to
10 days before use. Similarly, G. muris cysts of an isolate originally obtained
from hamsters (7) were purified from feces of infected athymic (nu/nu) mice and
stored before use. Cyst concentrations were determined with a Coulter Counter
(Model ZBI, Coulter Electronics, Hialeah, FL) and a haemacytometer. Except
where noted, cysts were added to water samples in concentrations of about
3×10^4/ml. Cyst viability was assayed by fluorogenic staining (8) and in vitro
excystation (7). In the former method, live cysts are distinguished by two
fluorescing dyes. One dye is fluorescein diacetate (FDA), which when absorbed
by cysts produces a fluorescent green only in live cysts; the second dye, either
propidium iodide (Pl) or ethidium bromide (EB), is excluded efficiently by live
cysts but absorbed by dead cysts, resulting in red fluorescence.
The following backpacker-type water filters were purchased from local retailers:
First Need Water Purification Device (First Need), General Ecology Inc.,
Lionville, PA; H2OK Portable Drinking Water Treatment Unit Model No. 6 (H2OK),
Better Living Laboratories Inc., Memphis, TN; Katadyn Pocket Filter (Katadyn),
Katadyn Products Inc., Wallisellen, Switzerland; and Pocket Purifier, Calco Ltd,
Rosemont, IL. Also noted in this category is the Water Tech Water Purifier
(Water Purifier), Water Technologies Corp., Ann Arbor, Ml. Although it is not
advertised as a filter and was not specifically tested for Giardia cyst removal,
we report qualitative observations made during disinfection testing (see below)
because its configuration and mode of operation suggest that particle removal
may occur. Physical and operating information provided in the filter packaging
is summarized in Appendix A. Each device was tested when it was new. Devices
that removed all cysts when new were retested after a period of use
approximating several months for a regular weekend user.
Each filter was prepared for testing by filtering four liters of tap water to
purge loose carbon particles or debris. The cyst removal performance of each
filter was determined by filtering one liter of spring water, turbidity of 0.1
NTU, to which formalin-fixed G. lamblia cysts had been added. The entire
filtrate volume was passed through a 25-mm dia., 5-um pore size, polycarbonate
membrane (Nuclepore, Pleasanton, CA). stained with EB (100 ug/ml), and mounted
under a cover slip. Cysts were counted at x250 magnification with the aid of
epifluorescence microscopy. A representative portion of each filter was
examined to quantify cyst recovery as described previously (9). The area
examined was inversely proportional to the number of cysts found and ranged from
3.5 percent of seeded positive control filters to 25 percent (one quadrant) of
filters with cyst densities less than one per field. Total numbers of cysts
present were estimated by extrapolation in direct proportion to the area
examined. In extensive work on recovery of Giardia cysts using the procedures
described above, cyst retention on the 5-um polycarbonate membrane in a single
filtration step has routinely averaged 80 to 90 percent (Ongerth JE:
unpublished). Accordingly, the ability to identify high levels of cyst removal,
which would result in passage of very few or no cysts, is excellent. This
ability is unaffected by the factors that contribute to lack of precision in
counting large numbers of cysts on filters; such inaccuracies usually occur when
only small representative subareas are examined and the total numbers are
estimated by extrapolation. A seeded positive control and an unseeded negative
control were processed with each batch of filter evaluations. The cyst removal
performance evaluation was replicated three times for each filter device, with
results expressed as the arithmetic average and corresponding standard
Contact Disinfection Testing
The Water Purifier is described in packaging information as a contact
disinfection device. Likewise, the H2OK and Pocket Purifier devices are
described as providing disinfection as well as removing cysts by filtration.
These devices were therefore tested for their effect on cyst viability in
addition to filtration efficiency. A single 500-ml sample for each device was
seeded with approximately 2.5 x 10^4 cysts and passed through the device.
Filtrate was collected and filtered as described above to recover cysts. The
viability of cysts was then assessed by FDA and EB staining as described below.
The cysticidal effects of seven commercially available and commonly used
disinfectant preparations were tested with identical procedures. Four of the
products were iodine based: Polar Pure Water Disinfectant (Polar Pure), Polar
Equipment, Saratoga, CA; Coghlan’s Emergency Germicidal Drinking Water Tablets
(CEGDWT). Coghlan’s Ltd, Winnipeg. Canada; Potable Aqua Drinking Water
Germicidal Tablets (Potable Aqua), Wisconsin Pharmacal Inc., Jackson, WI; and 2
percent iodine prepared from I2 reagent grade (Baker, Phillipsburg, NJ). The
remaining three products were chlorine-based: Sierra Water Purifier (Sierra), 4
in 1 Water Co., Santa Fe, NM; Halazone, Abbott Laboratories, North Chicago, IL;
and commercial liquid bleach (5.25 percent sodium hypochlorite). Disinfectant
solutions were characterized by pH and total halogen concentration (Appendix B),
the latter being determined colorimetrically using the DPD method.
Two water sources were used, one to reflect clear high-mountain conditions, the
other to reflect downstream, more turbid conditions. Water sources were
characterized by pH, turbidity, and free chlorine demand (Appendix C). The
upstream source was from a small, spring-fed tributary to the Snoqualmie River
near North Bend, Washington. Samples were taken from the stream approximately
50 yards downstream from the spring. The downstream source was the discharge
from Lake Washington in Seattle, Washington. Samples were taken in midstream at
the entrance to Portage Bay, adjacent to the University of Washington campus.
Water samples were prepared for testing by adding disinfectant, according to
manufacturers’ instructions, to one liter of water in stoppered glass bottles
Cysticidal properties of the chemical treatments were determined as follows.
1) Water was put in 50-ml disposable plastic centrifuge tubes and placed in a
2) G. lamblia cysts were added to each test sample at time zero.
3) Tubes were vortex-mixed, sampled, and returned to the incubator.
4) At each sampling time, i.e., time 0, 30 minutes and 8 hours, a 10-ml sample
was withdrawn; a portion was used for measuring disinfectant concentration, and
in the remainder the disinfectant was quenched with 0.1-mM sodium thiosulphate.
5) Cysts in the quenched sample portion were exposed to aqueous solutions of the
viability indicators, FDA (25 ug/ml) and EH (100 ug/ml), filtered on to a 13-mm
dia. 5-um pore-size filter membrane, and rinsed with distilled water (10 ml).
6) Filters were mounted on glass slides, sealed under coverslips and examined by
epifluorescence microscopy at x250 magnification (Model 16, Carl Zeiss, Inc.,
Thornwood, NY) to enumerate proportions of red and green fluorescing cysts
indicating dead and live status, respectively. The viability baseline of the
cysts was established by running a control sample of untreated water seeded with
cysts through each test, using procedures identical to those for disinfectant-
treated samples. Data are presented in terms of percent survival relative to
the controls (Figure 2). The effectiveness of each disinfectant for killing
cysts in both upstream and downstream water was determined in triplicate, with
results expressed as the arithmetic average and corresponding standard
The Water Tech Water Purifier, a contact disinfectant, was also tested as a
chemical disinfectant. The test water was 100 ml of spring-source water seeded
with Giardia cysts. The treated water was filtered, stained, and examined for
cyst viability as described in steps 5 and 6 above. Three replicates were
Inactivation of G. lamblia and G. muris cysts by heating was established as
follows. Cysts were added to distilled water in 15-ml glass test tubes. The
seeded tubes were incubated for 10 minutes at temperatures ranging from 10C to
70C. Afterwards, cyst suspensions were cooled immediately by swirling in 10C
water for one minute. Cyst viability was determined either by excystation or by
staining. If by the latter, FDA and EB were added to the samples, the tubes
were vortex-mixed, and a 1-ml aliquot was filtered through a 13-mm dia. 5-um
pore-size filter membrane. Filters were rinsed, mounted, and examined as
described above to enumerate the live and dead cysts.
Filter Device Tests
The four filters differed significantly in their ability to remove Giardia cysts
(Figure 1). The number of cysts recovered from water having passed through the
filter devices ranged from zero to greater than 10^4 in individual tests. The
performance of individual devices was consistent as indicated by the standard
deviations for each of the three replicate test sets (Figure 1). The percentage
of cysts removed by the devices, corresponding to 100 minus the percent of cysts
recovered from the filtrate, was 100 percent for the First Need and Katadyn
filters and approximately 90 percent for the H2OK filter. The concentration of
cysts in the Pocket Purifier effluent was not statistically different from the
The First Need and Katadyn filters were then subjected to a period of moderate
use and then retested. The volume of water processed during the simulated use
period was not the same for the two filters owing to differences in their
operation. The difference in volume had no apparent effect on performance of
the two filters. A total of 88 liters of tap water (turbidity of 0.3 NTU) was
filtered with the First Need. During the process it was back-flushed, as
recommended in package instructions, because the filtration rate decreased after
50, 71, and 75 liters had been filtered. After 88 liters had been processed,
the filtration rate was about 25 percent lower than when the filter was new, and
it was retested in that condition. The Katadyn filter was subjected to use by
filtering one liter of tap water four times a day for five days. At the end of
each day, the filter was cleaned according to package instructions by
disassembling, brushing the filter element, and allowing it to air-dry overnight
before reassembly. After the respective periods of use, these two filters were
tested in triplicate for efficiency of cyst removal. Performance of these
filters was the same, 100 percent cyst removal, when they were retested.
Contact Disinfection Devices – The effect of each of the contact disinfection
devices on G. lamblia cyst viability was limited. The Water Purifier
inactivated about 15 percent of the cysts added in 100 ml of upstream (low
turbidity) water; the H2OK filter inactivated about 5 percent of the cyst
challenge, and the Pocket Purifier inactivated about 2 percent of the cyst
Chemical Disinfectants – The effectiveness of seven disinfecting chemical
preparations ranged from only a few percent to greater than 99.9 percent,
depending on the chemical and its concentration, the contact time, and the
disinfectant demand of the water (Figure 2). None of the disinfectants was more
than 90 percent effective after a contact time of 30 minutes. After eight-hour
contact, the four iodine-based disinfectants, each caused a greater than 99.9
percent reduction in viable cysts. The chlorine-based disinfectants were
clearly less effective than the iodine-based ones at both contact times.
Heating in Water – Experiments conducted with cysts of G. lamblia and of G.
muris indicated that the two species have virtually the same sensitivity to
inactivation by heating. Cysts at both species were completely inactivated by
heating to 70C for 10 minutes. Heating to 50C and 60C for 10 minutes produced
95 and 98 percent inactivation, respectively (Figure 3).
To remove Giardia cysts from water, one must use a filter with sufficiently
small pores to trap the cysts and sufficiently large capacity to produce a
useful volume of treated water before backwashing or replacement is necessary.
Although a number of manufacturers advertise that their filters remove Giardia
cysts, the only previously published account of filter performance was for the
Katadyn unit (6). Our filter evaluation study showed that only the First Need
and the Katadyn filters removed cysts with at least 99.9 percent effectiveness.
Under the same test conditions, the H2OK filter was approximately 90 percent
effective and the Pocket Purifier was less than 50 percent effective for cyst
removal. The analysis of viability for the cysts collected in the effluent of
the Water Purifier, H2OK, and Pocket Purifier indicates that passage through the
device did not significantly reduce the percentage of viable cysts.
The current study showed that none of the chemical treatments could inactivate
more than 90 percent of cysts with 30 minutes of contact time at 10C. At both
30 minutes and eight hours of contact time, the iodine-based disinfectants
inactivated a higher fraction of cysts than did the chlorine-based products.
All methods inactivated a lower percentage of cysts in cloudy or turbid water
than in clear water. All disinfectants performed better with eight hours of
contact time than with 30 minutes. Only the iodine-based compounds inactivated
99 to 99.9 percent of cysts, within eight hours of contact time for both turbid
and clear water. As observed by Jarroll, et al (5), the 2 percent tincture of
iodine was less effective than the other iodine preparations with 30 minutes of
contact time, but it was as effective as the others at eight hours. Comparison
of our results with those of Jarroll, et al (5), is complicated by differences
between test conditions used. However, our results generally indicate more
stringent requirements for effective inactivation of Giardia cysts. Differences
between cyst populations used in the two studies could account for the observed
differences, even though both were G. lamblia. Cysts produced in our
trophozoite – gerbil system had consistently high intrinsic viability (>80
percent), excysted efficiently when fresh (80 to 90 percent), and have appeared
more resistant to halogen disinfectants than reported previously (Ongerth J.E.:
The results of heat inactivation in our study correspond to previous reports
indicating that heating to between 60C and 70C kills Giardia cysts efficiently.
In addition, our data illustrate the correspondence between the fluorogenic
staining and in vitro excystation procedures for assessing cyst viability. When
applied to cysts of the same condition. Staining indicates a slightly higher
proportion of viable cysts than does excystation. Overall, however, the two
procedures provide comparable information.
Figure 1 – Effectiveness of Four Portable Water Filters for Removal of Giardia
Cysts from One-Liter Volumes of Water Each containing approximately 3×10^4 Cysts
(dotted line). [A bar chart showing the positive and negative controls and
results from the filters, on a log scale. The First Need and Katadyn results
and the negative control were all zero. The Pocket Purifier and the positive
control were approximately the same – i.e. the Pocket Purifier did not remove
cysts at all. The H2OK results were somewhat below the positive control,
actually — due to the log scale — indicating 90% removal.]
Figure 2 – Effect of Time and Disinfectant Concentration of Seven Chemical
Disinfectants on Survival of G. lamblia Cysts in Turbid and in Clear Water. [A
rather striking bar chart comparing chemical treatments under varying
conditions. The chlorine compounds were basically ineffective, with no
significant effect at 30 minutes; at 8 hours the Sierra was still totally
ineffective, the bleach killed about half the cysts, and the Halazone killed 70-
90% of the cysts (better in clear water). The iodine compounds were poor at 30
minutes in turbid water (half killed), only a little better at 30 minutes in
clear water (70-90% killed, with Potable Aqua the best), but completely
effective (100% killed) after 8 hours.]
Figure 3 – Inactivation of Giardia Cysts as a Function of Temperature (10-minute
exposures) as Indicated by Ethidium Bromide Staining and by in vitro
Excystation. [A line chart showing cyst survival at different temperatures.
Four combinations of Giardia species, source, and laboratory technique are
shown, but all show approximately the same results. 40C kills no cysts; 50C
kills a lot of cysts, 60C kills most cysts, 70C kills all cysts.]
References to commercial products shall not be construed to represent or imply
the approval or endorsement by project investigators or sponsors.
Grant support was provided in part by the REI Environment Committee which
assumes no responsibility for the content of research reported in this
(1) Craun GF: Waterborne outbreaks of giardiasis: current status. In: Erlandsen
SL, Meyer EA (eds): Giardia and Giardiasis. New York: Plenum Press, 1984; 243-
(2) Kahn FH, Visscher BR: Water disinfection in the wilderness. West J Med
(3) Barbour AG, Nichols CR, Fukushima T: An outbreak of giardiasis in a group of
campers. Am J Trop Med Hyg 1980; 25:384-389.
(4) Ongerth JE, Butler R, Donner RG, Myrick R, Merry K: Giardia cyst
concentrations in river water. In: Advances in Water Treatment and Analysis,
Vol 15. Denver: Am Water Works Assoc, 1988; 243-261.
(5) Jarroll EL, Bingham AK, Meyer EA: Giardia cyst destruction: effectiveness of
six small quantity water disinfection methods. Am J Trop Med Hyg 1980; 29:8-11.
(6) Schmidt SD, Meier PG: Evaluation of Giardia cyst removal via portable water
filtration devices. J Freshwater Ecol 1984; 2:435-439.
(7) Schaefer FW III, Rice EW, Hoff JC: Factors promoting in vitro excystation of
Giardia muris cysts. Trans R Soc Trop Med Hyg 1984; 78:795-800.
(8) Schupp DG, Erlandsen SL: A new method to determine Giardia cyst viability:
correlation of fluorescein diacetate and propidium iodide staining with animal
infectivity. Appl Environ Microbiol 1987; 53:704-707.
(9) Ongerth JE, Stibbs HH: Identification of Cryptosporidium oocysts in river
water. Appl Environ Microbiol 1987; 53:672-676,
(10) American Public Health Assoc: Chapter 408E In: Standard Methods for the
Examination of Water and Wastewater, 15th ed. Washington, DC: Am Public Health
Assoc, 1980; 309-310.
Appendix A: Water Filter characteristics Listed by Manufacturers on Packaging or
[Manufacturer column omitted. See text for this information.]
Name Filter Type Operating Operating Useful Restrictions
Mode Rate Life /Limitations
First Need 0.4 um microscreen hand pump 1 pt/min up to 800 A
plus adsorber pints
H2OK 6 um mesh, 3 in. gravity 1 qt/min 2000 gal A, B
activated carbon w/Ag
Katadyn 0.2 um ceramic, hand pump 1 qt/min many years A
Pocket 10 um (nominal), halo- mouth – – A
Purifier genated resin (38% I), suction
Water Pur- Polystyrene resin bed gravity – 100 gal A, C
ifier (a) (46% I2 as I5)
A – Does not desalinate; not for saltwater or brackish water.
B – Pretreat with I2 for bacterially contaminated water.
C – Not for use with muddy water.
(a) Not described as a filter by package information.
Appendix B: Characteristics of Disinfectant Preparations
[Manufacturer column omitted. See text for this information.]
Name Active Chemical Recommended Application Total Halogen pH
Polar Pure Crystalline iodine, 1-7 capfuls per quart 2.4 (1 6.1
99.5% depending on temperature cap/quart)
CEGDWT Tetraglycine hydro- 1 tablet per liter or 4.5 (1 5.6
periodate 16.7% (6.68% quart tab/quart)
Potable Tetraglycine hydro- 1 tablet per liter or 5.3 (1 5.6
Aqua periodate 16.7% (6.68% quart tab/quart)
2% Iodine Iodine 0.4 ml per liter 4.5 6.5
Sierra Calcium hypochlorite & 100 crystals (50 mg) 11.6 6.7
hydrogen peroxide Ca(OCl)2 + 6 drops H2O2
Halazone p-dichloro-sulfamoyl 5 tablets per quart 7.5 6.7
benzoic acid, 2.87%
Chlorine sodium hypo-chlorite, 5 ml per gallon 3.9 7.1
(a) As prepared according to package instructions.
(b) In water treated according to package instructions.
Appendix C: Characteristics of Disinfectant Test Water
Source pH Turbidity (NTU) Chlorine Demand (a)
Spring-fed 6.8 0.09 0.3
Lake Washington 7.1 0.75 – 0.80 0.7
(a) 30 minutes, free chlorine demand (5).
Address reprint requests to Jerry E. Ongerth, PhD, PE, Assistant professor,
Department of Environmental Health, SB-75, University of Washington, School of
Public Health and Community Medicine, Seattle, WA 98195. Dr. Stibbs is with the
Department of Pathobiology, also at the School, and Mr. Macdonald is with the
Department of Medical Education, School of Medicine, both at the University of
Washington; Mr. Johnson is with the Department of Biological Chemistry, Johns
Hopkins School of Medicine, Baltimore; Dr. Frost is with the Office of
Environmental Programs, Department of Social and Health Sciences, Olympia, WA.
This paper, submitted to the Journal January 12, 1289, was revised and accepted
for publication June 22, 1989.
REI Water Filter Chart
REI Water Filters Comparison Chart:
Katadyne MSR PUR First Need
Minimum | .2 absolute | .1 absolute | 1.0 nominal |.4 absolute |
Pore Size | | | | |
Weight | 23 oz. | 19 oz. | 21 oz. | 14 oz. |
Number of | | | | |
Filter | 2 | 4 | 2 | 1 |
Elements | | | | |
Types of | Screen, |Foam, Screen | Glass Fibre,| Charcoal |
Elements | Ceramic |Carbon,Paper | Iodine resin| |
| |Membrane | | |
Cost Per | $.25 | $.28 | $.24 | $.37 |
Gallon | | | | |
Appr.Filter | | | | |
Life | 1000 | 500 | 500 | 100 |
(in Gallons)| | | | |
Approximate | | | | |
Filtering | 120 seconds | 90 seconds | 60 seconds | 90 seconds |
Time | | | | |
(in Quarts) | | | | |
Cost of | | Two Parts | | |
Replacement | $89.00 | $20.00 & | $40.00 | $24.00 |
Filter | | $30.00 | | |
Price | $225.00 | $140.00 | $130.00 | $37.00 |
For room reasons I left off two filters. Its specs are in order:
1.0 absolute, 12 oz., 2, Granular active carbin & ceramic, $.07,
1000, 60 MINUTES!, $40.00, $60.00.
2.0 absolute, 6 oz., 1, Spun Polypro, $.30,
100, 70 Seconds, $??.??, $30.00.
The filtering times are probably based on a new unit. Some units are
easy to clean, one can’t be properly, and one can be cleaned on the fly.
Lower prices can be found elsewhere than REI. REI charges list mostly.
Also note some units are easier to use (and clean) than others.
Katadyn MSR PUR 1stNeed line Designs
min pore size .2 .1 1 + I .4 2 1
dry weight 23 oz 19 oz 21 oz 14 oz 6 oz 12 oz
seconds/qt 120 90 60 90 70 grav- (when new)
seconds/qt 120 180 60 180 140 ity (after usage)
filter life 1000 500 500 100 100 1000 (in gallons)
cost/gallon $.25 $.28 $.24 $.37 $.30 $.07
retail price $225 $140 $130 $ 38 $ 30 $ 65
replacement $ 89 $ 50 $ 40 $ 24 n/a $ 40 (filter cost)
# elements 2 4 3 1 1 2
elements screen foam screen carbon polypro carbon
ceramic screen glassfiber ceramic
Notes: 1st Need, Timberline, and Basic Designs require iodine to treat
bacteria and viruses. Katadyn and MSR require iodine to treat viruses.
Only PUR requires no additional iodine. With carbon elements, only MSR,
1st Need, and Basic Designs remove harmful chemicals.
TABLE OF CONTENTS of this chain:
9/ Water Filter wisdom
10/ Words from Rachel Carson
11/ Snake bite
13/ Questions on conditions and travel
14/ Dedication to Aldo Leopold
15/ Leopold’s lot.
16/ Morbid backcountry/memorial
17/ Information about bears
18/ Poison ivy, frequently ask, under question
19/ Lyme disease, frequently ask, under question
20/ “Telling questions” backcountry Turing test
22/ Words from Foreman and Hayduke
23/ A bit of song (like camp songs)
24/ What is natural?
25/ A romantic notion of high-tech employment
26/ Other news groups of related interest, networking
27/ Films/cinema references
28/ References (written)
3/ Learning I
4/ learning II (lists, “Ten Essentials,” Chouinard comments)
5/ Summary of past topics
6/ Non-wisdom: fire-arms topic circular discussion
7/ Phone / address lists
8/ Fletcher’s Law of Inverse Appreciation and advice