depends on alot of things! Texasbob has your best answer. the well water is only going to be as good as the environment that surrounds it. Just like some people swear by "rain-water"...  The rain water in Los Angeles and larger more industrialized cities is going to be loaded with all the chemicals floating around in the environment. 

If you live in nice farmland away from the industrialization and smog and heavy traffic it might be good. I used to use tap water in my DWC until my city started getting fucky with their treatment. now i only trust distilled because its a blank canvas.