Interesting tidbit:
My son is taking a college class about water and was given a reading list to select a book from. TWTTKH was an option so he selected it cause he knew I would want him to.

Now he has to read the book and write about what water symbolizes in the book. That's his description, not mine. It has been a couple of years since I read the book, but I can't think of any water-related themes.