Sure, but nobody and nothing is standing out in the rain to "drink" the majority of their water intake. It's hard to think of any civilizations that relied on mostly rainwater, but maybe I haven't heard of any. What little prehistory I do comprehend suggests that consistent freshwater sources control patterns of human habitation (eg, most capitals are on rivers; Ur is a desert ruin because it is no longer a port city covered in greenery but was once).
Your point about diet is reasonable, but I still think it's probably "easier" to get it right in the water. No need for the body to move stuff to the kidneys if the water's already got some in it!
>Disclaimer: I drink reverse osmosis water every day with a ppm of about 8 compared to my tap which is 100 ppm. Rainwater varies but is probably about 8 ppm. :)
Parts per million of what? Maybe I'm stupid and that stands for "particles per milliliter"?
