Adam Clarke on Jeremiah 15:18

Wilt thou be altogether unto me as - waters that fail? - Leaning either springs, which in the height of summer grow dry; or, like that phenomenon in the sandy desert, where, by a peculiar action of the air on the rising vapors, the resemblance of water is produced, so that the traveler, deceived, rejoices that he is come, in the sandy desert, to the verge of a beautiful lake; but the farther he travels, it is still at the same distance, and at last vanishes; and he finds the whole was an illusion, for the waters have failed. Nothing can exceed the disappointment of the farmer whose subsistence absolutely depends on the periodical rains, when these fail, or fall short of their usual quantity. Some times the rice is sown and springs up in the most promising manner; but the latter rains fail, and whole fields of young rice wither and perish.