re: The West is dry, and we didn't plan well. We need a system to move water from Midwest

They have plenty of water. They choose not use it. Rain water in rivers and cities mostly flows freely into the ocean.

2019
Despite California’s long drought, trillions of gallons of rainwater wastefully flowing into sea.

In February alone, an estimated 18 trillion gallons of water fell on the state. In urban areas and coastal cities, 80 percent ends up diverted into the ocean, as Los Angeles and other cities built long concrete channels for flood control.

Why make freshwater when we could collect the water that falls from the sky? Even on the driest year in recorded history in 2013, it still rained 3.6 inches in Los Angeles. An inch of rainfall in L.A. generates 3.8 billion gallons of runoff, so you’re talking about more than 12 billion gallons of water that could be captured, but that flows within hours down our concrete streets and into the ocean. There’s enough rainwater to be harvested to produce 30-50% of the entire city’s water needs.