Exodus 7:19 - Clarke's commentary and critical notes on the Bible

And the LORD spake unto Moses, Say unto Aaron, Take thy rod, and stretch out thine hand upon the waters of Egypt, upon their streams, upon their rivers, and upon their ponds, and upon all their pools of water, that they may become blood; and that there may be blood throughout all the land of Egypt, both in vessels of wood, and in vessels of stone. That there may be blood - both in vessels of wood, and in vessels of stone - Not only the Nile itself was to be thus changed into blood in all its branches, and the canals issuing from it, but all the water of lakes, ponds, and reservoirs, was to undergo a similar change. And this was to extend even to the water already brought into their houses for culinary and other domestic purposes. As the water of the Nile is known to be very thick and muddy, and the Egyptians are obliged to filter it through pots of a kind of white earth, and sometimes through a paste made of almonds, Mr. Harmer supposes that the vessels of wood and stone mentioned above may refer to the process of filtration, which no doubt has been practiced among them from the remotest period. The meaning given above I think to be more natural.