Exodus 15:23-25

When they came to Marah, they couldn’t drink its water. It was bitter. That’s why the place is named Marah. The people told Moses they weren’t happy with him. They said, “What are we supposed to drink?” Then Moses cried out to the LORD. The LORD showed him a stick. Moses threw it into the water. The water became fit to drink. There the LORD gave a ruling and instruction for the people. And there he tested them.