The fact is, we have transported cultures and lifestyles developed in places with plenty of water into the semiarid western US and presided over a massive population growth in the last half century. Something will have to change.

....it might be better to say that the Medieval West had a different climate than it has had during most of American history, one that was fundamentally more arid. And there’s no reason to assume that drought as we know it is the aberration. Ingram notes that the late 1930s to early 1950s—a time when much of the great water infrastructure of the West was built, including the Hoover Dam—may turn out to have been unusually wet and mild on a geologic time scale.....
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These mega-droughts aren’t predictions. They’re history, albeit from a time well before California was the land of Hollywood and Silicon Valley. And the thought that California and the rest of the modern West might have developed during what could turn out to be an unusually wet period is sobering. In 1930, a year before construction began on the Hoover Dam, just 5.6 million people lived in California. Today more than 38.2 million live in the largest state in the U.S., all of whom need water.