Charles Ellicott Commentary Leviticus 11:38

"But if water be put upon the seed, and [aught] of their carcass fall thereon, it is unclean unto you." — Leviticus 11:38 (ASV)

But if any water be put upon the seed. —The case, however, is different when the grain is moistened, because the fluid softens the grain, and thus enables the defilement of the carcass to penetrate into its very fibers. The wet grain therefore is regarded in the same light as porous clay vessels which become saturated with defilement, and must be broken. (Compare Leviticus 6:28.) By water, according to the rule which obtained during the Second Temple, the seven liquids mentioned in Leviticus 11:34 are meant.