Then Moses led the people of Israel away from the Red Sea into the desert of Shur. For three days they walked through the desert, but found no water.
Then they came to a place called Marah, but the water there was so bitter that they could not drink it. That is why it was named Marah.
References for Exodus 15:23
The people complained to Moses and asked, "What are we going to drink?"
Moses prayed earnestly to the Lord, and the Lord showed him a piece of wood, which he threw into the water; and the water became fit to drink. 1 There the Lord gave them laws to live by, and there he also tested them.
References for Exodus 15:25
He said, "If you will obey me completely by doing what I consider right and by keeping my commands, I will not punish you with any of the diseases that I brought on the Egyptians. I am the Lord, the one who heals you."
Next they came to Elim, where there were twelve springs and seventy palm trees; there they camped by the water.