Exodus 15:22-25 NIV

[22] Then Moses led Israel from the Red Sea and they went into the Desert of Shur. For three days they traveled in the desert without finding water. [23] When they came to Marah, they could not drink its water because it was bitter. (That is why the place is called Marah.) [24] So the people grumbled against Moses, saying, “What are we to drink?” [25] Then 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 fit to drink. There the LORD issued a ruling and instruction for them and put them to the test.