really depends on the grade of filter your using. Some higher grade cardridges will filter out more stuff than others. Personaly I like the products at http://www.spectrapure.com/
Little more money, but In my Opinion, worth it. you really got to dig into the specs on the cardrige your getting, to see what all it is supposed to remove. the smaller the micron rating, the better it filters.you can get almost any brand to fit your unit.