"Uh, sir, how are we supposed to get through this lava?"
>"Why can't you just go through it?"
"Well, it's pretty hot you see"
>"Well then just bring a fan with you and stop complaining already."
Makes sense if you ask me.
Magic.
More realistically, there'll probably be wells like on scorched earth. Possibly also a new electrical/tek machine which gathers water from the air.