September 15, 2008 
Almost all drinking water filters employ carbon as the primary fitration medium. Carbon filters are used to remove a wide variety of chemical pollutants. They are especially effective on organic chemicals, such as pesticides, herbicides and industrial chemicals. They’re also effective in removing radon, chlorine, and bad tastes and smells. When good quality carbon filters are properly used, they remove 80 to 99 percent of the organic chemicals, radon, chlorine and bad tastes and smells in water. However, they don’t remove microorganisms or toxic minerals. Only a high quality reverse osmosis system can remove 99.99% of drinking water pollutants. In addition, carbon filters have a finite lifetime. Typically, a household of four people uses about 1 1/2 gallons of drinking water per day, or 2 1/2 gallons per day if filtered water is also used for cooking. This translates into approximately 500 to 1,000 gallons per year. Manufacturers of full-size carbon filters may claim their filters are effective for 2,000 gallons or more, but it is recommended that many carbon filters be changed every six months depending on the brand. This ensures optimum performance and minimizes the chances of pollutant breakaway. Small carbon filters that attach to a faucet may even have to be replaced every few months.
Excerpted from “The Drinking Water Book” by Colin Ingram.