You need to complete the "Build a Bond" quest and receive the Ice Crystal Butterfly Deer to unlock the area where the Fountain is located. There's no Reputation level requirement for this. Once the Fountain is repaired, you will be able to get some energy back after spending 500 Energy (any energy spent in Treasure Adventure, Farm Flashback, and Cloud Farm counts). Tap the Water Jugs to claim the returned Energy.

You can upgrade the Fountain to get more Energy per each 500 Energy spent. You can also upgrade the Water Jugs to have more Jugs in which to store the Energy.