In Ezekiel 47, where did the water of the great river come from?

Answer: Under the temple threshold

Ezekiel saw water flowing from under the threshold of the temple toward the east, growing into a river too deep to cross.

“Then the man brought me back to the entrance of the temple, and I saw water flowing from under the threshold of the temple toward the east (for the temple faced east). The water was coming down from under the south side of the temple, south of the altar.”— Ezekiel 47:1 (BSB)