underground water in deserts?
I have a desert civilization that supposedly isn't near any above-ground water sources. What I'd like to know is...
How underground rivers/underground seas come to be,
How likely they are to appear beneath a desert (of the really sand-duney variety, heh),
Is the water pure enough to use, and...
Would there be any changes on the surface of the earth that somebody would notice and realize there's water down there?
[EDIT]Real-life examples would be helpful, but not necessary[/edit]
How underground rivers/underground seas come to be,
How likely they are to appear beneath a desert (of the really sand-duney variety, heh),
Is the water pure enough to use, and...
Would there be any changes on the surface of the earth that somebody would notice and realize there's water down there?
[EDIT]Real-life examples would be helpful, but not necessary[/edit]