There is a lot of pollution around, and a lot of abuses of the natural resources. For example, on I-80 in Nevada, it is not uncommon to see some sort of man-made factories around what appears to be natural hot-springs (what do they usually do?), plus there's also always a danger of natural pathogens like E. coli.
Is there any good way to determine if a given body of water (lake, salt lake, hot spring) is safe to submerge oneself into?