There are some vary sound reasons why towns and cities sprouted up around natural sources of fresh water. LA and Las Vegas were both quite small communities until fresh water was directed toward them through massive engineering projects. If/when those projects stop working water will become a massive, critical, lethal issue.

It also has to be noted that as the world climate warms, and climate bands shift, the Midwest and West are becoming dryer. Places that enjoyed adequate rainfalls are seeing less total rain. What rain they are getting is coming as torrential rains that runs off instead of soaking in. With drought being followed by flood as the massive rainfall overload the waterways.