Which son did Jacob call "uncontrolled as the waters" for defiling his father's bed?

Answer: Reuben

Reuben was Jacob's firstborn, but "uncontrolled as the waters" (KJV: "unstable as water"), he would no longer excel.

“Reuben, you are my firstborn, my might, and the beginning of my strength, excelling in honor, excelling in power. Uncontrolled as the waters, you will no longer excel, because you went up to your father’s bed, onto my couch, and defiled it.”— Genesis 49:3-4 (BSB)