Water Filters & Filtration Techniques


Water filters remove impurities and contaminants from water, making it safer for drinking, cooking and other uses. These filters come in many shapes and sizes -- from models designed to filter the water supply as it enters the home to small units that fit on a personal water bottle -- and use different filtration technologies. Understanding the different types of filters and their functions can help you find the right filter based on your needs and the specific contaminants in your water.

Choosing Water Filters

  • The contaminants found in your local water supply will determine what water filtration is best for your home. The U.S. Environmental Protection Agency publishes frequent reports that specify contaminants found in water systems around the U.S. If you rely on well water, you may wish to hire a testing agency to provide you with information about your water quality. Once you know what contaminants are found in your water, NSF International -- an independent public health and environmental organization -- provides information on filters that are certified to remove those specific pollutants. If you're dealing with lead or sulfur, for example, NSF provides a list of filters that can remove these substances. The Environmental Working Group, or EWG, provides a similar list of filters designed to remove specific compounds or chemicals.

Carbon Filters

  • Most small point-of-entry water systems, such as those that attach to a kitchen faucet, rely on some form of activated carbon filter. These filters vary significantly in their effectiveness, according to the EWG. Carbon block filters, which are made using pulverized carbon formed into solid blocks, are more effective at filtering water than granulated carbon filters, which are made using fine granules of carbon.

Ceramic Filters

  • Some systems use ceramic filters rather than standard carbon units. These filters consist of a layer of thin ceramic equipped with numerous small holes that block particles and contaminants. Ceramic filters cannot block most chemicals, according to the EWG.

Filter Pore Sizes

  • To compare the effectiveness of different filters, look for the pore size, measured in microns. The smaller the pores, the fewer contaminants will be able to pass through. Microfiltration particles, with pores ranging from 0.05 to 5 microns, are ineffective at removing chemicals and viruses and only moderately effective at removing bacteria, according to the Centers for Disease Control and Prevention. Ultrafiltration filters have pores ranging from 0.001 to 0.05 micron, with an average pore size of 0.01 micron. These filters are highly effective at removing bacteria, moderately effective at removing viruses and poor at removing chemicals. Nanofiltration filters, with an average pore size of 0.001 micron, are highly effective at removing bacteria and viruses and moderately effective at removing chemicals.

Other Options

  • If you prefer a system that's more advanced than a standard water filter, or you're looking for a whole-house water treatment system, consider reverse osmosis or ion exchange systems. Reverse osmosis units, which push water through a semipermeable membrane, remove many contaminants that carbon filters leave behind, according to the CDC. Ion exchange units primarily reduce minerals like calcium and magnesium to soften water. While they can remove some contaminants like lead and sulfate, they do not remove bacteria or viruses, according to the CDC.

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