2 Kings 2:21

And cast the salt in there - He cast in the salt at the place where the waters sprang out of the earth. Jarchi well observes here, "Salt is a thing which corrupts water; therefore, it is evident that this was a true miracle." What Elisha did on this occasion, getting the new cruse and throwing in the salt, was only to make the miracle more conspicuous. If the salt could have had any natural tendency to render the water salubrious, it could have acted only for a short time, and only on that portion of the stream which now arose from the spring; and in a few moments its effects must have disappeared. But the miracle here was permanent: the death of men and cattle, which had been occasioned by the insalubrity of the waters, ceased, the land was no longer barren; and the waters became permanently fit for all agricultural and domestic uses.