Albert Barnes Commentary Jeremiah 2:18

"And now what hast thou to do in the way to Egypt, to drink the waters of the Shihor? or what hast thou to do in the way to Assyria, to drink the waters of the River?" — Jeremiah 2:18 (ASV)

Sihor - The Nile. To lean upon Egypt was a violation of the principles of theocracy.

The two rivers are the two empires, and to drink their waters is to adopt their principles and religion. Compare also (Isaiah 8:6–7).