Exodus 15:23-25

When they came to Marah, they couldn’t drink the water because it tasted bitter. That’s why the place was called Marah [Bitter Place]. The people complained about Moses by asking, “What are we supposed to drink?” Moses cried out to the LORD, and the LORD showed  him a piece of wood. He threw it into the water, and the water became sweet. There the LORD set down laws and rules for them to live by, and there he tested them.