Comentario sobre Exodo 7:24

לא יכלו לשתות מים מן היאור, “they could not drink the waters from the river.” Even when the river again flowed with water, they could not drink those waters as they had become putrid from the dead fish that had died when the water had turned into blood. This explanation does not appear to stand up in light of what the Torah writes, as we have been told specifically (verse 25), that “seven days elapsed after the Lord had struck the river.” In other words, the plague ran its course for a whole week, unless we must understand that line to mean that after the blood reverted to being water the Egyptians still could not drink from the river for a full week.