This phrase emphasizes that they are the direct, physical descendants of Judah. Alternate translation: "are the descendants of Judah"
# the waters of Judah
The word "waters" here is a euphemism for semen. You may need either to translate using a different euphemism or to specify the meaning of the euphemism. Alternate translation: "the family line of Judah" or "the loins of Judah" or "the sperm of Judah" (See: [[rc://en/ta/man/jit/figs-metonymy]])