Comment by jerf

The Great Lakes have a management principle that is basically "You can use the water of the Great Lakes by permission as long as the water remains in the watershed." And permission is not automatic either.

The reason for that to a large degree is that the Great Lakes area looked over at the Southwest, which wasn't even as bad at the time as it is now, did some math, and worked out that if the Great Lakes tried to supply the Southwest that it would cause noticeable dropping of the water level. I'm sure it would be even more dropping now.

The problem is, the Great Lakes aren't just some big lakes with juicy fresh water that can be spent as desired. They are also international shipping lanes. They make it so that de facto Detroit, Chicago, and a whole bunch of other cities and places are ocean ports. Ocean ports are very, very valuable. There are also numerous other port facilities all along the great lakes, often relatively in the middle of nowhere but doing something economically significant. This is maintained by very, very large and continual dredging operations to keep these lanes open. Dropping the water levels would destroy these ports and make the dredging operations go from expensive to impossible.

So, getting large quantities of water out of the Great Lakes to go somewhere isn't just a matter of "the people who control it don't want to do that", which is still true, and a big obstacle on its own. The Southwest when asking for that water is also asking multiple major international ports to just stop being major international ports. That's not going to happen.