Albert Barnes Commentary Jeremiah 13:1

"Thus saith Jehovah unto me, Go, and buy thee a linen girdle, and put it upon thy loins, and put it not in water." — Jeremiah 13:1 (ASV)

A linen girdle - The appointed dress of the priestly order (Leviticus 16:4).

Put it not in water - that is, do not wash it, and so let it represent the deep-grained pollution of the people.