If Moses and Aaron turned all the water in the Nile into blood, skeptics ask where the Egyptian magicians got the water to mimic the plague.

There are two solid answers. First, Exodus 7:24 tells us that the people dug by the side of the river for fresh water. Additionally, fresh water from the Nile's source outside of Egypt would have kept flowing, replacing the 'blooded' water within a matter of a couple of days.

However, a stronger contextual answer is that when the text states the Egyptian magicians 'did the same' or 'did so by their arts,' it does not necessarily mean they literally repeated Moses' performance at that very moment. Rather, it means that turning water into blood was part of their known repertoire of tricks. Since the Plagues were a contest of honor between the gods of Egypt and the God of Israel, the magicians had enough honor status in Pharaoh's eyes to simply appeal to their existing magical arts. An ancient record that said it could be done would be sufficient when combined with their personal honor and authority, meaning there is no need to worry about where they procured more water to do the trick simultaneously.