What do Activated Carbon Filters Remove?

Activated carbon filters are best at removing chlorine and bad tastes or odors, but may be certified to remove other contaminants. Look for the NSF certification on a carbon filter to find out exactly what it's capable of removing.
Bad tastes and odors? YES
Chlorine? YES
Trihalomethanes (THMs)? YES
Mercury? YES
Pesticides and herbicides? YES
Iron or heavy metals? If certified
Lead? If certified
Bacteria? If certified to remove coliform
Hard water? NO
Fluoride? NO
Total dissolved solids (TDS)? NO
Dissolved minerals like calcium and magnesium sail right through a carbon filter. However, a carbon filter with a pore size smaller than one micron can remove coliform, cysts, lead, arsenic, or iron and other heavy metals through mechanical filtration. Even though these contaminants don't adhere to the carbon, they cannot fit through the small pores. 
Often materials are added to carbon to improve its reduction capabilities. Adding silver to carbon creates a media that kills bacteria. Iron-reduction carbon includes KDF (Kinetic Degradation Fluxion) media made of ground copper and zinc to create a chemical reaction. The KDF converts heavy metals from a ferrous (dissolved) to a ferric (solid) state to capture the solids in the matrix of the carbon. Although certain carbon blends can reduce coliform, a UV system disinfects bacteria-infested water most effectively.