"E.P.A. reports show that U.S. water supplies contain over 2300 cancer causing chemicals..." Ralph Nader Research Group
They also give a great rundown of all the major water filters by price, capacity, cost per gallon, cost per year and what each filters out. This is exactly the sort of thing you need when your eyes are glazing over in the CVS or Duane Reade and it kills you to fork over another $25 for one of these filter replacements. Turns out the Brita tap mount is one of the cheapest over the course of a year.