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 sweet. There the Lord made a decree and a law for them, and there he tested them.
He said, "If you listen carefully to the voice of the Lord your God and do what is right in his eyes, if you pay attention to his commands and keep all his decrees, I will not bring on you any of the diseases I brought on the Egyptians, for I am the Lord, who heals you."
~ Exodus 15:25-26, NIV