"Don't drink the water and don't breathe the air."
As for the air, it is generally clean in the US. Sort this chart by "above or below world average": [2] Also note the line about the US being very well sampled, so if there's an error it's not there.
It isn't 1965 anymore.
[1]: http://en.wikipedia.org/wiki/Drinking_water_quality_standard...
[2]: http://www.guardian.co.uk/environment/datablog/2011/sep/26/g...