When testing your water, understanding water filter jargon can make a difference.
Which model works best?
First and foremost, have your water tested and determine what specifically needs to be filtered. Despite 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.
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