Anyone getting a water filter should make sure they are NSF 42 and 53 certified.

Here are some of the chemicals and percent reductions that NSF 53 certified filters meet:

Asbestos 99%
Benzene 99%
Carbon Tetrachloride 98%
Chlordane 99.5%
Chloroform (TTHM)* (surrogate chemical) 99.8%
Ethylbenzene 99%
Ethylene Dibromide (EDB) 99%
Lead (pH 6.5) 99.3%
Lead (pH 8.5) 99.3%
Mercury (pH 6.5) 99%
Mercury (pH 8.5) 99%
Toluene (Methylbenzene) 99%

Go to NSF.org for the longer more complete list.