The Berkey has double or quadruple filters. The black filters IIRC filter out chemicals and heavy metals and the white ones filter out pathogens. I'd also have backup filters. If you are going to be filtering turbid water, you may want to consider building a sand filter to pre-filter the water - this will vastly extend the life of the filters. Remember, you will need a minimum of 1 gal/day/pp.

I don't own a Geiger counter and I live at Ground Zero. Spend the money on other more valuable items. Also, make sure you have Where There is No Doctor in PDF. Also same books available for dentist and vet. Also have a book for local medicinal herbs. And a first aid book. Read and learn.