Filtering water is a good idea because in addition to herbicides, pesticides and such, there is the issue of pharmaceuticals like Prozac, antibiotics, birth control, etc. finding their way into pubic water supplies.
http://www.epa.gov/nerlesd1/chemistry/ppcp/media03.htm
Prozac was recently discovered in Denton streams and therefore in the food chain. Scientists can only speculate on what the full ramifications of this will be.
http://www.google.com/search?hl=en&ie=U ... +bluegills
I personally wouldn't drink any unfiltered water from a public source or a well these days. There's just too much toxicity in the environment.