Question

Which routes have Waterfalls in X/Y?

Answer 1

Route 15 - North of east bridge
Route 16 - Northern area (requires Cut)
Frost Cavern - West of the exit to Dendemille Town
Couriway Town - South of the hotel
Pokemon Village - Northwest area
Route 22 - South of the stairs near the exit; south of the Chamber of Emptiness
Victory Road - Northeast of pier

Waterfall (Bulbapedia)

Answer 2

If I remember correctly, the routes that have waterfalls are Route 22, Route 21, Frost Cavern(Outside), Victory Road, Route 15, Pokemon Village, and I think that's it. Hope I Helped!