You get HM Waterfall on Route 18. It's near the place where you find Rook, one of the Seven Sages, all the way to the end of the route.
I hope I helped! :D
See related link below for a tutorial.
route 18
Surf, cut, fly, strength, waterfall, and dive
all pure water types can learn waterfall ( like panpour and other water types
HM Waterfall can be found at the very end of route 17, the route west of Nuvema and Accumula Towns.
HM Waterfall can be found on Route 18 in Pokemon Black and White.
to bad
route 18
On route 18
on route 18
yes
you get it in route 18
Somewhere on route 18
Route 18.
it is at route 18, in corner on farthest island
See related link below for a tutorial.
it is found on the ground at route 18