Ex 15:23-27

23they arrived at Marah, where they could not drink its water, because it was too bitter. Hence this place was called Marah. 24As the people grumbled against Moses, saying, “What are we to drink?” 25he cried out to the LORD, who pointed out to him a piece of wood. When he threw it into the water, the water became fresh.^h

It was here that God, in making statutes and ordinances for them, put them to the test. 26He said: If you listen closely to the voice of the LORD, your God, and do what is right in his eyes: if you heed his commandments and keep all his statutes, I will not afflict you with any of the diseases with which I afflicted the Egyptians;ⁱ for I, the LORD, am your healer.

27Then they came to Elim, where there were twelve springs of water and seventy palm trees, and they camped there near the water.^j