In just about every list of the ten plagues, the water turning to blood comes first. It’s a little confusing, because one might casually think that Moses’ staff turning into a serpent would be first, but that’s “only” a miracle.
The water turning into blood was a plague because it affected everyone. The point of this plague is to take the miracles of God—and, therefore, His authority—out of Pharaoh’s court and out towards the people. Soon enough, everyone would be impacted by God’s power, even if Pharaoh stubbornly failed to admit it himself.
Curiously, it seems that the plague only affected the Egyptians. Several times in this stretch of Scripture, God talks about the “Egyptians” difficulty in finding water. Exodus 7 talks about “their” streams and “their” pools.
Does this mean that the Israelites weren’t affected? It’s possible, especially since later plagues only affected the Egyptians.
This has led a lot of people to assume that the Egyptians had to beg water from their Israelite slaves in order to survive. I don’t think the Text supports that idea, primarily because Exodus 7:24 says that the Egyptians had to dig “around the Nile” to find water.
This minor detail reveals a huge shift in the lives of the Egyptians. For most of them, they lived on, or near, the Nile. It was a focal point of their lives, so much so that you can trace the development of the civilization by proximity to this all-important body of water. If something happened to the Nile, Egypt was lost.
To harness this power, early Egyptians developed an ingenious irrigation system that funneled water directly to their crops. They didn’t need wells like other people did during that time period. The fact that they had to start digging wells—a practice which was probably foreign to most of them—shows just how much this plague affected them.
Just like the staff-to-serpent miracle, Pharaoh’s magicians were able to “duplicate” this miracle, but I would argue the similarities were pretty mild. The Text talks about a plague so expansive that it spread to ponds, pools, and all the “reservoirs of water,” which are most likely cisterns.
Furthermore, the plague itself didn’t just change the color of the water, it changed the composition of it as well. The water was so putrid that it killed all the fish inside, which would’ve impacted the Egyptian economy by itself.
This was a major plague—one that, interestingly enough, isn’t ever explicitly stated as being removed by God (at least as revealed in the Text; it probably filtered out). All the other plagues will be removed by the intervention of Moses, but the Nile turning into blood lingered. Most likely, it stayed in the minds of the Egyptians for a lot longer.
