No single water filter technology will eliminate all types of contaminants, but some treatment devices use more than one method to rid water of nearly all contaminants. Once you’ve identified your specific problem, you can choose a water-treatment solution that is right for it.
Reverse-osmosis (RO) filters. For water with multiple contaminants, a reverse-osmosis filter is often the best solution. It will remove inorganic chemicals such as salts, metals (including lead), minerals, nitrates, asbestos, and, because most models include carbon pre-filters and post-filters, catch organic chemicals such as pesticides, as well as trihalomethanes (THMs) and radon. Not all remove chlorine, so if this claim is made, request proof. The carbon post-filter is used to improve the water’s aesthetic properties. Pre- and post-filter cartridges should be replaced annually.
Most RO systems mount beneath the sink and connect directly to the plumbing. A small tank stores clean water until needed, and tainted water drains out through a line connected to the sink trap. With most, drinking water flows through a special, separate sink-top spout or may be routed to an ice maker or water cooler.
Conventional RO filters waste about 3 gallons for every gallon of pure water they produce; some have an automatic valve that prevents excessive waste. RO filters generally cost from $400 to $600.
Distillers. Another device that will remove almost everything from water is a distiller. Distillers electrically heat water until it turns into steam; the steam then condenses and turns back into water in a separate chamber, leaving behind 99 percent of the health- and aesthetic-related pollutants.
Countertop models must be filled manually, use a lot of electricity, and may take several hours to produce 1 gallon of water, but they are relatively inexpensive at from $100 to $300.
Activated carbon (AC) filters. If your water tastes, smells, or looks bad, a filter containing activated carbon (AC) will probably make it much more palatable. Many AC filters also remove chlorine, pesticides, herbicides, radon, THMs, and some inorganic chemicals, but not all carbon filters effectively reduce lead content. If you’re concerned about lead, be sure the unit you’re considering is certified for lead removal. Solid-block and precoat absorption filters trap lead.
Though a carbon filter will remove mercury, don’t count on a conventional one to remove all metals, salts, nitrates and nitrites, and organisms. In fact, be aware that a carbon filter will accumulate the contaminants it cleans from water, and the resulting bacteria may even breed in it, so it’s very important to replace filter cartridges religiously, according to the manufacturer’ s recommendations.
Effectiveness of a particular carbon unit is directly related to the amount of activated carbon it contains. Beneath-the-counter systems with dual filters typically cost from $100 to $200. The $30 faucet-end models are only marginally effective. Whole-house point-of-entry (POE) systems, recommended where a contaminant such as radon poses a threat to the entire house, cost $500 or more.
Ultraviolet (UV) disinfection devices may kill bacteria and viruses, and improve the taste and odor of water, but they are not effective against chemical pollutants and may not work against cysts and spores. In some carbon filter units, ultraviolet is used to kill bacteria.
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