Exodus 7:22-25

22But again the magicians of Egypt used their magic, and they, too, turned water into blood. So Pharaoh’s heart remained hard. He refused to listen to Moses and Aaron, just as the Lord had predicted.

23Pharaoh returned to his palace and put the whole thing out of his mind.

24Then all the Egyptians dug along the riverbank to find drinking water, for they couldn’t drink the water from the Nile.

25Seven days passed from the time the Lord struck the Nile.