"Buy and dry" is the default outcome. Cities buy the farms nearby, use the farms' water rights and let the fields go dry. Agriculture uses 60-90% of the water in the west depending on river basin. Cities can afford MUCH higher rates per gallon for water than farmers can so the cities will eventually just buy out the farmers if nothing changes. I have no worries about Denver or Las Vegas or LA running out of water. There just might not be water intensive crops grown out west anymore.