Exodus 7:20 Immediately Moses and Aaron did just as Jehovah had commanded. He lifted up the rod and struck the water that was in the Nile River before the eyes of Pharʹaoh and his servants, and all the water that was in the river was turned into blood.
Why would someone argue that in Revelation 16 a similar thing will not be literal?
Revelation 16:4 The third one poured out his bowl into the rivers and the springs of water. And they became blood. 5 I heard the angel over the waters say: “You, the One who is and who was, the loyal One, are righteous, for you have issued these judgments, 6 because they poured out the blood of holy ones and of prophets, and you have given them blood to drink; they deserve it.” 7 And I heard the altar say: “Yes, Jehovah God, the Almighty, true and righteous are your judgments.”