go to Sootopolis, then go to the cave of origin. You will find a pokeballl in there in which contains the TM Waterfall
The way you get waterfall is by trading the waterfall HM from Fire Red Version or the other Version that have waterfall HM ( you can trade with a link cable or wireless adaptor)
in the cave of origin
In Pokémon Ruby Sapphire and Emerald versions, HM7 contains the move waterfall. You can find the HM in the Cave of Origin.
go to Stevens haus! near the trees.
HM08 Waterfall is in the Cave of Origin in Sootopolis City.
look around in mossdeep for Stevens house and it's there
in the cave in sootoplis city when your going to fight groundon
Somewhere on route 18
Steven will give it to you
you have to have beaten the elite 4 and givenh celio on island one the ruby you go to island 4 and find hm 7 waterfall in waterfall cave
its past Fallabour town, you need the HM waterfall to access that part
cave of origin. sotopolis city when you need to fight groudon