Eventually water from the Missouri River drainage basin needs to be transported to the Colorado River drainage basin.

I have been amusing myself thinking about how to do this with the least wait time, and for the least money.

Boring a tunnel or burying a pipeline would take forever on legal and water/property rights alone.

My current thought is a large water treatment plant should be built on one of the southern tributaries of the Missouri basin that lies overtop an underground aquifer that extends even further southward, hopefully hundreds of miles. Highly filtered and UV light purified water from Missouri basin should be pumped down into the first aquifer. Geologists should locate a spot where this first aquifer lies overtop a second underground aquifer that extends even further south, hopefully all the way to the Colorado basin’s northern most tributary. A second pumping station should be built there. Tunnels or pumping stations should then get the water flowing into the Colorado basin.

The first, second (and maybe third) pumping stations must have a strong electrical grid tie. However they do not need to pump at a steady rate - they should consume electricity during periods of low demand, such as late night, or increase pumping when unsteady power generators like windmills are experiencing high winds.

A federal tax should be levied on Colorado water users to fund this.
The tax rate should be high enough to pay States in the Missouri River Basin large $ grants to improve their overall water and sewage systems

This is all pretty simple pre-existing engineering, except for the core drilling to confirm aquifers.

Since it is all simple,
IT WILL NEVER GET DONE