The category of VOC (Volatile Organic Chemical) includes a number of chemicals that are both man-made and naturally occurring. Water from wells and utilities may contain some of these contaminants. Some VOCs are pesticides, herbicides, or insecticides that seep into the ground water after application. Other VOCs enter the water supply through industrial or other waste disposal. This category also includes total trihalomethanes, which are a by-product of chlorination.

A VOC reduction claim by the manufacturer means the system reduces the concentration of all of the following contaminants:

alachlor                      endrin                          simazine 
atrazine                      ethylbenzene                    styrene
benzene                       ethylene dibromide (EDB)        1,1,2,2-tetrachloroethane
carbofuran                    haloacetonitriles               tetrachloroethylene
carbon tetrachloride            bromochloroacetonitrile       toluene
chlorobenzene                   dibromoacetonitrile           2,4,5-TP(silvex)
chloropicrin                    dichloroacetonitrile          tribromoacetic acid
2,4-D                           trichloroacetonitrile         1,2,4-trichlorobenzene
dibromochloropropane (DBCP)   haloketones                     1,1,1-trichloroethane
o-dichlorobenzene               1,1-dichloro-2-propanone      1,1,2-trichloroethane
p-dichlorobenzene               1,1,1-trichloro-2-propanone   trichloroethylene
1,2-dichloroethane            heptachlor                      trihalomethanes (TTHM)      
1,1-dichloroethylene          heptachlor epoxide                bromodichloromethane
cis-1,2-dichloroethylene      hexachlorobutadiene               bromoform
trans-1,2-dichloroethylene    hexachlorocyclopentadiene         chlorodibromomethane
1,2-dichloropropane           lindane                           chloroform
cis-1,3-dichloropropylene     methoxychlor                    xylenes                      
dinoseb                       pentachlorophenol