Bill Stock wrote:

What kind of wood for a water wheel,

Pretty much anything, so long as it's a _working_ wheel. It's the
non-moving decorators that have the problems.

Wet wood lasts well and doesn't rot. It's _damp_ wood that has the
problems. If you wet the timber and keep it wet (i.e. submerged or
rotating continuously), then it'll last (for most timbers, most
conditions). You can also use timbers (such as elm) that are normally a
problem for beetle attack.

Personally I'd use white oak, because it's local and traditional. Your
local heavyweight softwoods might survive equally well. Look at what
the local fashion was, about 100 years ago.