Elisha prayed upon the water, and they were healed.

2 Kings 2:19-22

And the men of the city said unto Elisha, Behold, I pray thee, the situation of this city is pleasant, as my lord seeth: but the water is naught, and the ground barren. And he said, Bring me a new cruse, and put salt therein. And they brought it to him. And he went forth unto the spring of the waters, and cast the salt in there, and said, Thus saith the Lord, I have healed these waters; there shall not be from thence any more death or barren land. So the waters were healed unto this day, according to the saying of Elisha which he spake.