To get HM07 Waterfall in Pokémon FireRed, travel to Icefall Cave on Floe Island where the HM is located on the first floor. Navigate through an ice puzzle to the ledge near the entrance to floor B1F.Continue Reading
Floe Island is the fourth island players arrive at during the Sevii Islands side quest. The Island is reached by boat after receiving the Rainbow Pass from Celio. In order to receive the Rainbow Pass, retrieve the Ruby Gem from Mt. Ember.
After arriving on Floe Island, travel to the cave on the Northeast section of the island. Use surf to get across the small body of water in front of the cave.
Each floor contains several ice puzzles. Walk across ice tiles to reach HM07. Do not walk on the same tile twice, as this means you risk falling through to floor B1F.
HM07 Waterfall appears as a pokéball icon on the bottom right ledge on the first floor. Slide across the room to the ledge, and press A to pick up the item. This can be done before or after engaging in a battle with Team Rocket.