I’ve included links to the info used for each state below.(Corrections accepted with a link to the source.) Thanks to Andre for corrections regarding Ohio, and Georgia, September 21, 2014.
Also note that there are over 3000 counties in the U. It is entirely possible that rain water harvesting may be subject to additional laws not found on the state government websites.
Also note that in Texas, the right to harvest rain water is actually protected by law.
Update; June 1, 2015: Some new information on Nevada.
Update; April 10, 2015: Its been over a year since the last post on this topic.
Sadly, lots of the links we put here to state gov’t webpages on rain water harvesting have been moved, or perhaps simply removed.