Household jug water filters have become very popular - usually to
remove the taste of chlorine and/or potential domestic water supply
contaminants such as: lead, chlorine, fluoride, trihalomethanes
(water chlorination by-products), iron, manganese. Filters are often
preferred, especially indoors, to bottled water because of lower
cost and greater convenience.

Sometimes there is hope that a filter will also remove or reduce the
risk of waterborne diseases like: Cryptosporidium, Giardia, E.coli,
Salmonella.

I have recently investigated how safe and effective a jug filter is
likely to be. My primary interest was in the question of silver
toxicity - especially when people self-medicate with colloidal
silver. Actually there does not seem to be any reason for concern
about silver toxic effects from these common household filtration
cartridges, but I did turn up a number of other health risks (and
potential health benefits) from filtered water...

What's in a Jug ("Pitcher" in U.S. English) Filter?
--------------------------------------------------
Jug filters normally comprise granular activated carbon (GAC) and a
weak base ion exchange resin impregnated with silver ions. The ion
exchange resin serves to replace the calcium and magnesium ions in
the water with hydrogen ions, thereby softening the water and
reducing pH (i.e. making the water slightly more acidic). GAC
removes chlorine and SOME organic material from the water. The
silver ions act as a (bacteriostatic) biocide to reduce bacterial
accumulation in the filter cartridge. "Bacteriostatic" means that
the silver tends to control numbers of bacteria, rather than totally
eliminate them. However, the risk of infection by food poisoning
bacteria is often dose-related i.e. reducing numbers can have a
significant protective effect in some cases.

Effectiveness of Jug Drinking Water Filters
-------------------------------------------
[edited extract from http://www.homeenv.com/art_wtr_filt.htm]

Chlorine is one of the easiest contaminants for carbon to remove -
there is adequate carbon in a typical cartridge for NSF Class I
chlorine removal. Filter cartridges are much less efficient for
removing other contaminants such as trihalomethanes, MtBE, MX, trace
pesticides/herbicides, and many other VOC's because these potential
contaminants require more carbon "contact" time.

Carbon filters will not usually remove all dissolved inorganic
contaminants (dissolved solids e.g. heavy metals). Some carbon
filters will remove lead and some copper but other dissolved
inorganics will pass through unobstructed: dissolved minerals/salts,
antimony, arsenic, asbestos, barium, beryllium, cadmium, chromium,
copper, fluoride, mercury, nickel, nitrates/nitrites, selenium,
sulfate, thallium, and certain radionuclides. With the exception of
lead and fluoride, removing these contaminants requires either a
reverse osmosis water filter system (RO system) or a water
distiller. Lead can be removed through specialty carbon filters and
there is a type of activated alumina cartridge that can be used for
fluoride removal.

Safety Concerns and Precautions for Risk-free Use
-------------------------------------------------
[edited extract from
http://www.unitedutilities.com/resources/files/40_WaterHealth_Issue_34.pdf]

An extensive UK study came up with the following conclusions about
jug-filtered water:

* A significant reduction in pH in filtered water.

* Bacterial levels were slightly higher in the filtered water
compared to the feed water, but overall there was no evidence that
jug water filters had an adverse effect on microbial water quality.

* If the filter was used beyond the designated lifetime (normally
28 days) there was an increase in bacterial numbers in the filtrate.

* A difference in taste and odour between filtered and unfiltered
water, this was due to the removal of chlorine by the filter.

* Bacterial numbers were high in the first litre filtered after a
period of non use. (Manufacturers normally recommend that the first
two litres of water should be discarded).

* Higher concentrations of silver ions in the filtrate than the
feed; the levels declined as the water filter aged. There is limited
toxicity data on the presence of silver in drinking water and
currently no regulatory standard.

* Elevated levels of nickel in the filtered water after boiling.

* Filters were spiked with high concentrations of the foodborne
pathogens: Salmonella and Escherichia coli to simulate cross-
contamination of the filter from general activities in the kitchen.
These organisms were only present in the first litre filtered after
their introduction. This suggests that the silver ions do act as an
effective biocide.

World Health Organization Report
--------------------------------
[edited extract from
http://www.who.int/water_sanitation_health/dwq/WSH02.07.pdf]

Charcoal and activated carbon have been used extensively as
adsorbents for water treatment in the developed and developing
world. Charcoal or activated carbon will adsorb microbes, including
pathogens, from water, but dissolved organic matter in the water
rapidly takes up adsorption sites and the carbon rapidly develops
a "biofilm" coating. Therefore, carbon is not likely to appreciably
reduce pathogenic enteric microbes in water over an extended period
of time. If anything, carbon particles are prone to shedding
microbes into the product water, thereby reducing the microbial
quality.

In many point-of-use devices the carbon is impregnated or commingled
with silver that serves as a bacteriostatic agent to reduce
microbial colonization and control microbial proliferation in the
product water. Fecal indicator bacteria, such as total and fecal
coliforms, and opportunistic bacterial pathogens, such as Aeromonas
species are capable of colonizing carbon particles and appearing in
product water. For these reasons, activated carbon is not
recommended as a treatment method to reduce pathogenic microbes in
drinking water. Additional treatment, such as chemical disinfection,
often is needed to reduce microbe levels in carbon-treated water.
Mixed media containing carbon along with chemical agents effective
in microbial retention have been developed and evaluated. For
example, carbon filters containing aluminum or iron precipitates
have been described, and these filters have achieved appreciable
microbial reduction in tests.

Granular activated carbon filter media prepared with chemical agents
which are more effective in retaining microbes may eventually become
more widely available for point-of-use treatment of household water.
However, the conventional charcoal and activated carbon media
currently available for water treatment are not recommended for use
at the household level to reduce microbial contaminants. Only
charcoal or activated carbon media that been combined with other
materials to improve microbial reductions should be considered for
household treatment of collected and stores water and then only if
there are performance data or certifications to verify effective
microbial reductions.

Limitations of Silver in Filter Cartridges
------------------------------------------
[edited extract from
http://www.who.int/water_sanitation_health/dwq/WSH02.07.pdf]
Silver is used as a bacteriostatic agent for point-of-use or
household water treatment by storing water in vessels composed of
silver or passing water through porous or granular filter media
impregnated with silver. However, the extent to which silver alone
inactivates microbes in water is limited, bacteria may develop
silver resistance and many microbes, such as viruses, protozoan
cysts and oocysts and bacterial spores, are not inactivated at
silver concentrations employed for point-of-use drinking water
treatment.

Author: Michael Meredith http://www.lovehealth.co.uk
[This article may be distributed freely with the attribution that it
is copied from "Cambridge Healing - Holistic Lifestyle Group":
http://health.groups.yahoo.com/group/cheal/]