The places with the most sunshine and some of the most fertile land happen to be far away from places with rivers. The rivers are not a grid and we can't pull

The places with the most sunshine and some of the most fertile land happen to be far away from places with rivers. The rivers are not a grid and we can't pull anything close to the full flow of the river for our uses without serious agricultural consequences. A national(or international) water grid allows us to distribute our impact on regional water supplies.