Quite likely it depends. If most of the rock formations in the area are relatively insoluble such as granite or sandstone, it might not be too bad. Steel Blue could find it pretty bad in Alabama which has plenty of limestone.
I think many here worry too much about mineral content. If you fill the radiator and add very little over say a 2 year period before changing, all but the worst water isn't going to cause a problem. If you are continually adding, it would be better to fix the leak. In the mean time, better listen to Ryan.