Jamieson, Fausset & Brown

snow water--thought to be more cleansing than common water, owing to the whiteness of snow (Psa 51:7; Isa 1:18). never so clean--Better, to answer to the parallelism of the first clause which expresses the cleansing material, "lye:" the Arabs used alkali mixed with oil, as soap (Psa 73:13; Jer 2:22).