Exodus 15:25 New International Version (NIV)

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.

2 Kings 2:21 New International Version (NIV)

²¹ Then he went out to the spring and threw the salt into it, saying, “This is what the Lord says: ‘I have healed this water. Never again will it cause death or make the land unproductive.’”