As someone who moved to LA in the early 70s, and left LA in the late 80s, and spent some time to visit Palm Springs, Phoenix, and Las Vegas, I can say with full confidence that anyone with a lick of sense knew there was not enough water to sustain that growth that started back then, but that didn't stop anyone from building or buying those homes. They all knew it, but didn't care.
It was, and still is, plain old stupid to build those giant cities in those barren deserts. The idea that we'd all have to pay for pipelines to push that water all those miles feels a bit painful to me now, and the complete lack of any discussion about the environmental impact of doing this very bothersome too.
There are many other issues to consider, like the quality of that Mississippi water. They don't call that river "The Big Muddy" for nothing. And there is still a lot of industry that use and dumped used water into it, and farms that have runoff of pesticides all along it and it's tributaries.
The total driving distance from New Orleans to Las Vegas is 1,722 miles. I doubt you can route a pipeline in a way that reduces that much. The cost and environmental impact of building one would be enormous.
This plan feels like it was concocted by someone who's never driven from Las Vegas to New Orleans, or spent anytime on or around the Mississippi River. It gets low on water too. There are droughts in the mid-west too.
Truth is there is no good sustainable solution to this problem as it exist. The only reasonable solution is to stop building new homes right now, and look into how to reduce the number that exists because it's obvious they've already overbuilt.
It's hard for me to imagine anyone with a lick of sense taking this seriously, but that's a shortcoming of mine I am well aware of nowadays.