Unfortunately, water has the nasty habit of dissolving salt. As the Lake Peigneur Disaster taught us, mixing the two is generally a really bad idea.

That's how they create the salt caverns in fact: they pump hot water below impermeable limestone formations that were created when Kansas was an ocean 290 million years ago during the the Permian period. They use seismographs to watch the cavern formation and steerable drill bits to shape the formation.