Exodus 15:22-25

22Then Moses led the Israelites away from the Red Sea. They travelled into the desert called Shur. They walked into the desert for three days and they could not find any water to drink.

23Then they arrived at Marah. But they could not drink the water there because it was too bitter. That is why they called that place ‘Marah’.

24Then the people complained. They spoke against Moses. They said, ‘There is nothing for us to drink!’

25Then Moses called to the Lord for help. The Lord showed Moses a special tree. Moses threw a branch into the water. Then the water became good for them to drink. There at Marah, the Lord made a law for the Israelites to obey. He tested them there, to see if they would trust him.