Understanding Water Filter Jargon

advertising claims, no filter can remove all water
contaminants – and some remove too many beneficial
minerals. No nonelectric filter can remove live bacteria.
These must be eliminated by boiling or in a separate,
prefiltration chlorine-treatment stage.

Some filters contain a single (ceramic or
carbon/ion-exchange) element; others offer multistage
filtration combining two to five of the following
filtering/purification systems:

Mechanical particulate filter elements of
fine-grained, porous ceramic that strain out dirt, sediment
(turbidity) and other particles, including asbestos,
parasitic flukes and their egg cysts, and some large
bacteria. The government pure-water filtering standard is
.05u (half a micron), but some filters will eliminate
particles as small as .01u – small, but larger than most
bacteria. Many portable hiker’s ceramic filters can be
renewed by simply scraping off the outer surface on the
rough leg of your jeans.

Activated carbon filters contain beads of
bone charcoal (elemental carbon) that are superheated/dried
to become ionized, so they naturally attract metallic
elements and many stray organic molecules. They capture
lead, mercury, chlorine, sulfur, VOCs (volatile organic
chemicals such as the pesticide Lindane) and biological
sources of bad taste and odor. Carbon filters can be partly
restored by washing and superdrying.

Reverse osmosis filters force water
through a semipermeable membrane that removes salt, heavy
metals, most chemicals and many other microscopic
impurities, including VOCs and nitrates. They do
not reliably filter out bacteria.

Ion-exchange filters, as used in
single-cartridge, faucet-mount filters and in large water
softeners, expose water to plastic beads coated with
ionized salts that capture nitrates, many minerals,
including lead and mercury, and the iron, magnesium and
calcium that can give water an off-color or off-taste. Some
can be recharged — and contaminants washed away — in a
disposable bath of strong brine, so they can be used for
years. WARNING: One of our editors sees a dentist who warns
against too-soft, overdemineralized water (such as
steam-distilled “pure spring water”), as it deprives us of
minerals that are essential to lifelong strong teeth and
bones.

UV generators, included in some
top-of-the-line, multistage home countertop, undercounter
and central filters, expose water to natural ultraviolet
(sunburn) light radiation that kills living parasites and
bacteria, but not all cysts and eggs (these must be
filtered out in another stage).

Save instruction sheets and be sure to clean, renew or
replace filter or purification elements as indicated — some
after a given number of months, others after a number of
gallons of water.