"And the LORD showed him a tree, and he threw it into the water, and the water became sweet..."

God granting water and manna to the Israelites in the wilderness (source) 

   
"Then Moses led Israel onward from the Red Sea, and they went into the wilderness of Shur; they went three days in the wilderness and found no water. When they came to Marah, they could not drink the water of Marah because it was bitter; therefore it was named Marah. And the people murmured against Moses, saying, "What shall we drink?" And he cried to the LORD; and the LORD showed him a tree, and he threw it into the water, and the water became sweet. There the LORD made for them a statute and an ordinance and there he proved them, saying, "If you will diligently hearken to the voice of the LORD your God, and do that which is right in his eyes, and give heed to his commandments and keep all his statutes, I will put none of the diseases upon you which I put upon the Egyptians; for I am the LORD, your healer." Then they came to Elim, where there were twelve springs of water and seventy palm trees; and they encamped there by the water."
-Exodus 15:22-27, read at Great Vespers for Theophany
  
(source)
  

Prophet Moses (source)

  

Through the prayers of our Holy Fathers, Lord Jesus Christ our God, have mercy on us and save us! Amen!