I live in Lawrenceville and even though I have never tested tap water for nitrates, I have never had a problem with nitrates in any of my tanks that I know of. I use the API test kit for the tank water tests.
I had one type of test kit, just for nitrates that reads it at 12.5, I then bought a reef kit from a different manufacture and it also reads 10.. Of course the colors, for me, are hard to distinguish sometimes..
See this link: http://www.gwinnettcounty.com/departments/publicutilities/pdf/waterwords_2005.pdf">http://www.gwinnettcounty.com/departments/publicutilities/pdf/waterwords_2005.pdf</a>
It is from 2005 but it says nitrates is 10ppm for Gwinnett
Ok. So you got me curious. I tested my tap water with a Salifert Nitrate test and it is between 1-2ppm. I live in Forsyth County Suwanee and get my water from Lake Lanier.