Adam Clarke on Psalms 58:7

Let them melt away as waters - Let them be minished away like the waters which sometimes run in the desert, but are soon evaporated by the sun, or absorbed by the sand.

When he bendeth his bow - When my adversaries aim their envenomed shafts against me, let their arrows not only fall short of the mark, but he broken to pieces in the flight. Some apply this to God. When he bends his bow against them, they shall all be exterminated.