Use it. I've been using water out of a pond for a few years now without any apparent problems. Maybe doing a sophistocated indoor hydro setup you have the luxury of fretting about PPM, EC, pH, and whatever else, but out in the woods you take what you can get. Within reason of course. If it is sulfur water drainage from an old coal mine, you probably want to shy away. You guys that live or lived in a old mining town know what I mean.