(the) Interstate Canal System
For thousands of years humans have been able to take water from one place and bring it to another. This was accomplished with tunnels, canals and aquaducts.
That said, my proposal is to connect existing water systems- rivers, streams, lakes, etc. using technology we already have. To accomplish this we can dig canals, install tunnels, pipelines and aquaducts.
This way when one section of the USA is dry/ in a drought stage, the sections of the USA that have rain can share that bounty with those who are less fortunate.
Another advantage of my system is that it could, if applied properly, alleviate flooding.
It will also put many Americans back to work. The only issue is where is the money going to come from?