We live in a modern post-industrial nation, so people dying of thirst is not acceptable here.

How out of hand things get makes a difference. Just a little bit and the Federal government should stay silent and leave matters to the State and its Governor. But when things get WAY WAY out of hand, the State and its Governor failed to act effectively so the Federal government can now step in and bring its resources to save the lives of US citizens. The Federal jurisdiction is intrinsic and inherent but is appropriately activated ONLY when the state falls down on the job. When a city in Texas runs out of water, the Federal government has a right and a duty to prevent loss of innocent life in that city. This could be done by bringing water or by transporting out the local residents to some other place, possibly in a different state