Before we come to settle these four questions, let's first delve a bit into the words of the early commentators on this matter:

Regarding the verse, "And the magicians of Egypt did so with their enchantments," which indicates that the magicians also showed their power by turning water into blood – the early commentators questioned where the magicians found water for this purpose, since all the water in Egypt had turned into blood.

We find several answers to this question:

In "Daas Zekeinim MiBaalei HaTosafos," they wrote: "Where did they get the water from? They brought it from another place. Alternatively, from water that they dug up."

In "Moshav Zekeinim," they explained that the magicians brought water from Goshen, where the waters were not struck. Similarly, Rabbi Chaim Paltiel wrote in his commentary that they did this in the land of Goshen. And according to the words of the Midrash (Shemos Rabbah Parsha 9, Siman 10), which states that when the Egyptians took water from the Israelites for money, it remained water, we can also say that the magicians took water from the Israelites for money and then turned that water into blood.

Another answer we find in the words of Rabbi Yosef Bechor Shor (also brought in "Moshav Zekeinim" and "Chizkuni"), who established a principle on the matter: "It appears to me that the Nile did not remain blood throughout, but only at that moment. When it turned to blood, the fish died, and afterward, it turned back into water. You should know that it does not say they couldn't drink from the Nile because it was blood, but because the fish died and their carcasses stank. And it also says that the magicians did the same – what did they do, since everything was blood, even in vessels, as it says: 'and in wood and in stone'? Certainly, the blood was only temporary throughout the land of Egypt, and afterward, it turned back into water, and then the magicians turned it back into blood temporarily. Therefore, Pharaoh did not tell Moses and Aaron to turn it back into water, but since he saw that it immediately turned back into water, he did not pay attention to it."