Book about a man transported to a desert world. Buildings are made from salt and urine might be eliminated as solids

Kind of a longshot, because I have fuzzy memories of this at best, really only the beginning of it. A man from our Earth somehow gets transported to a desert world where buildings are made out of salt because there's so little water. He thinks he's entirely human until he tries to urinate and finds that he excretes crystals instead, all water being retained in his body. I want to say that he compares himself to a kangaroo rat at that point.

I read this in middle school or so, so it's late 80s at the oldest, and probably older. I read it as a paperback in my brother's sci-fi/fantasy collection.