Activated carbon (AC) filters have been used in home water purification systems primarily to remove taste and odor. Taste and odor, although undesirable, are generally not considered unhealthy. In recent years, however, AC filters have been used to remove some of the contaminants that have been discovered in water supplies.
AC is most effective at removing organic compounds
such as volatile organic compounds, pesticides and benzene. It can also remove some metals, chlorine and radon. As with any treatment system, it cannot remove all possible drinking water contaminants.
Because AC systems are limited in the types of
compounds they can effectively remove, it is essential that the homeowner determine which water contaminants are present before purchasing such a system. Anyone who suspects they have a water quality problem should first have their water analyzed by their local health department
or a reputable laboratory. These analyses are costly, but worth the expense since they are necessary to determine the appropriate home treatment system and how best to operate such a system. A state or local health official can interpret water analysis results. Some laboratories may also provide this service.
Note that home water treatment is considered only a temporary solution. The best solutions to a contaminated drinking water problem are to either end the practices causing the contamination or change water sources.
AC is a black solid substance resembling granular or powdered charcoal. It is extremely porous with a very large surface area. Certain contaminants accumulate on the surface of the AC in a process called adsorption.
 Figure 1- Active Carbon Filtration System |
The two main reasons that chemicals adsorb onto AC are a "dislike" of the water, and attraction to the AC. Many organic
compounds, such as chlorinated and non-chlorinated solvents, gasoline, pesticides and trihalomethanes can be adsorbed by AC. AC is effective in removing chlorine and moderately effective in removing some heavy metals. AC will also remove metals that are bound to organic
molecules. It is important to note that carbon is not necessarily the same as AC. AC removes vastly more contaminants from water than does ordinary carbon.
Home AC treatment systems are quite simple. The AC is normally packaged in filter cartridges that are inserted into the purification device. Water needing treatment passes through the cartridge, contacting the AC on its way to the faucet. AC filters eventually become fouled with contaminants and lose their ability to adsorb pollutants. At this time, they need to be replaced. AC treatment systems are typically point-of-use (POU) --- installed where they typically treat water used for drinking and cooking only. AC filters can be placed on
the end of the faucet, on the countertop, or under the sink. POU systems often have a bypass so that water for purposes other than drinking and cooking can also be dispensed at the tap without being treated. This increases the life of the AC, reducing the time between filter replacements.
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How-To: Information about Activated Carbon Water Treatment
