2 Kings 2:19-22

Then the men of the city said to Elisha, “Look, this city is in a pleasant place, as my lord [Elisha] sees; but the water is bad and the land is barren.” He said, “Bring me a new jar, and put salt in it.” So they brought it to him. Then Elisha went to the spring of water and threw the salt in it and said, “Thus says the LORD: ‘I [not the salt] have purified and healed these waters; there shall no longer be death or barrenness because of it.’ ” So the waters have been purified to this day, in accordance with the word spoken by Elisha.