Can you sculpt lasting statues in waterbased clay?
Yes, if you fire it (cook it in a kiln) to the point where it is
"vitrified," at which point it essentially becomes another
substance. In the process, the water is driven out, the clay
particles become dense, and the piece becomes waterproof. Fired
clay pots and sculptures (or, at least, fragments of them) have
lasted for thousands of years.