Exodus 7:19-20

19The Lord said to Moses, “Tell Aaron, ‘Take your staff and stretch out your hand over the waters of Egypt—over the streams and canals, over the ponds and all the reservoirs—and they will turn to blood.’ Blood will be everywhere in Egypt, even in vessels of wood and stone.” 20Moses and Aaron did just as the Lord had commanded. He raised his staff in the presence of Pharaoh and his officials and struck the water of the Nile, and all the water was changed into blood.