EWG launches US tapwater database.

Quick start:

1. Enter your zip code or state, no account required. 
2. Click your city and get a report on the city water quality. 

The results show the number of pollutants above healthy recommendations, and "other contaminants". EWG also provides a link to filters to filter these out. The Berkey filters have the best filtration ability, but no filter takes all amounts of all contaminants out.
Here is where National News also tested the tap water of 239 cities.

More info

1. EWG tapwater database. 
2. Learn about pharmaceuticals in US streams.
3. How to filter out poisons from your water. Comprehensive article and link to Berkey filter results.