Smarter Living: Water & Air

If you found, following the steps in "Do You Need a Home Water Filter?," that there are contaminants in your water and that a filtering system will get rid of them, use this guide to help you select the right filter for your home.

Household water filters generally fall into one of two categories: point-of-entry units, which treat water before it gets distributed throughout the house; and point-of-use units, which include countertop filters (e.g. filter pitchers), faucet filters, and under-the-sink units. Some filters use more than one kind of filtration technology.

When choosing a filter, make sure it is certified as meeting NSF/ANSI standard 53. NSF-certified filters have been independently tested to show that they can reduce levels of certain pollutants under specified conditions. Those that meet standard 53 are geared toward treating water for health, not just for aesthetic qualities. While the NSF certification program is not flawless, it does provide some assurance that at least some claims made by the manufacturer have been verified.

To select the filter that is best for your home:

Step One

Consult the list below to determine which type of filtering system will remove the contaminants in your water.

Activated Carbon Filter

  • Gets rid of: Bad tastes and odors, including chlorine. An activated carbon filter bearing NSF Standard 53 certification will filter out most pollutants of concern, including heavy metals such as copper, lead and mercury; disinfection byproducts; parasites such as Giardia and Cryptosporidium; pesticides; radon; and volatile organic chemicals such as methyl-tert-butyl ether (MTBE), dichlorobenzene and trichloroethylene (TCE). But be advised, there are contaminants, for example perchlorate, a rocket fuel ingredient, which a simple countertop filter will not be able to remove. Use the searchable directory in step #2 below to find the right filters for you.
  • Used in: Countertop, faucet filters and under-the-sink units.
  • How it works: Positively charged and highly absorbent carbon in the filter attracts and traps many impurities.

Cation Exchange Softener

  • Gets rid of: Calcium and magnesium, which form mineral deposits in plumbing and fixtures, as well as barium and some other ions that can create health hazards.
  • Used in: Whole-house, point-of-entry units.
  • How it works: "Softens" hard water by trading minerals with a strong positive charge for one with less of a charge.


  • Gets rid of: Heavy metals such as cadmium, chromium, copper, lead and mercury, as well as arsenic, barium, fluoride, selenium and sodium.
  • Used in: Countertop or whole house point-of-entry units; can be combined with a carbon filter.
  • How it works: Boils water and re-condenses the purified steam.

Reverse Osmosis

  • Gets rid of: Most contaminants, including certain parasites such as Cryptosporidium and Giardia; heavy metals such as cadmium, copper, lead and mercury; and other pollutants, including arsenic, barium, nitrate/nitrite, perchlorate and selenium.
  • Used in: Under-the-sink units; often in combination with a carbon filter or UV disinfection unit.
  • How it works: A semi-permeable membrane separates impurities from water. (Note: This filtration technique wastes a substantial amount of water during the treatment process.)

Ultraviolet Disinfection

  • Gets rid of: Bacteria and parasites; class A systems protect against harmful bacteria and viruses, including Cryptosporidium and Giardia, while class B systems are designed to make non-disease-causing bacteria inactive.
  • Used in: Under-the-sink units, often in combination with a carbon filter and sediment screen.
  • How it works: Ultraviolet light kills bacteria and other microorganisms.

Step Two

Once you've got a good idea of the type of filter that can address your water quality problem, visit the searchable directory of NSF/ANSI Certified Drinking Water Treatment Units. In the Reduction Claim field, highlight those contaminants that you need to reduce, then click search. The resulting list of certified filters should meet your particular needs

To find a dealer in your area, see the Water Quality Association's online listings.

A note about maintaining your filter properly

No filter will give you good performance over the long term unless it receives regular maintenance. As contaminants build up, a filter can not only become less effective, but actually can make your water worse, by starting to release harmful bacteria or chemicals back into your filtered water. To keep your filter working properly, follow the manufacturer's maintenance directions. Some filters only require a cartridge change, while others are better maintained by a certified professional. Many filter distributors offer maintenance and service contracts for their products. Before buying any water treatment system, compare not only filter prices, but also operating and maintenance costs for the different units.

last revised 8/12/2011

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