Earlier quoted context omitted.
Water from the Great Lakes cannot leave the Great Lakes. The Great Lakes Compact prevents construction of any water withdrawal that will move water outside of the watershed. https://en.m.wikipedia.org/wiki/Great_Lakes_Compact
By act of Congress, not Constitutional amendment. It could be repealed in a matter of weeks if Congress saw fit.
So - support for that repeal might prove scarcer than you'd think, from just looking at a map of drought-plagued areas of the U.S.
Also - burning needs for water tend to be sudden & immediate things. Vs. designing, approving, funding, and building the infrastructure to actually move large quantities of water long distances is more of a "decade-plus time scale" thing.