I use NSW in my 6gal nano FOWLR, in my office at work. So far so good, after 8 months, and in a 6gal tank there is not that much room for error.
I collect water in the bay in port washington.
My advice is to collect water where there is good water movement, Stay away from still water.
When you collect, use something like a gallon water jug and put it under the water with the cap on and take off the cap under water. This way if there is any petroleum products floating on the surface, you wont pick it up.
Im kid of a newbie, but you should check out PaulB's threads and articles.
He has been using NSW for 38 years in the same tank.