Exodus 7:24
And all the Egyptians digged round about the river for water to drink; for they could not drink of the water of the river. And all the Egyptians digged round about the river for water to drink; for they could not drink of the water of the river.
Exodus 7:24 belongs to the first plague, in which all the waters of the river were turned to blood. The river involved was the Nile, revered by the Egyptians as sacred and life-giving and worshiped by many as a god. The bloodied water remained undrinkable and unusable for seven days. The water became putrid and the fish died.
Because the river water could not be drunk, the Egyptians had to dig round about beside the river for drinking water. The plague exposed the Nile's inability to protect or help its worshipers and showed Jehovah's power over an object of Egyptian idolatry. Before the stroke, Moses and Aaron faithfully warned Pharaoh of the nature and effect of the coming plague, so he could escape it by letting Israel go to serve and sacrifice to God in the wilderness, and judgment fell only upon his refusal.
The plague did not humble or soften Pharaoh, but he hardened his heart and remained unmoved. The miracle increased Pharaoh's hatred of the Israelites, because the work of his magicians led him to believe it was performed by magic. Later judgments gave Egypt evidence that God was acting.