The "streams" mean the natural branches of the Nile in Lower Egypt. The word "rivers" should rather be "canals"; they were of great extent, running parallel to the Nile, and communicating with it by sluices, which were opened at the rise, and closed at the subsidence of the inundation. The word rendered "ponds" refers either to natural fountains, or more probably to cisterns or tanks found in every town and village. The "pools", literally "gathering of waters," were the reservoirs, always large and some of enormous extent, containing sufficient water to irrigate the country in the dry season.

In vessels of wood - The Nile water is kept in vessels and is purified for use by filtering, and by certain ingredients such as the paste of almonds.

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.

And the Lord spake unto Moses,.... Pharaoh still being obstinate, and refusing to let the people go:

say unto Aaron, take thy rod, and stretch out thine hand upon the waters of Egypt; upon all of them in general, what were in the river Nile, or derived from it, as follows:

upon their streams; the seven streams of the river Nile; see Gill on Isaiah 11:15.

upon their rivers; the canals that were cut out of the river Nile, for the watering of their fields and gardens, for they had no other river:

and upon their ponds, and upon all their pools of waters; which were dug near the river, or to which pipes were laid to convey the water thither:

that they may become blood; and so not fit to drink:

and that there may be blood throughout all the land of Egypt,

both in vessels of wood, and in vessels of stone; in which water were kept in private houses, fetched from the river for the use of families; all which were to be turned into blood everywhere, in all parts of the land, and in all places mentioned, immediately upon Aaron's taking his rod, and smiting the waters with it in that part of the river that was before him.

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.

pools...: Heb. gathering of their waters

7:14-25 Here is the first of the ten plagues, the turning of the water into blood. It was a dreadful plague. The sight of such vast rolling streams of blood could not but strike horror. Nothing is more common than water: so wisely has Providence ordered it, and so kindly, that what is so needful and serviceable to the comfort of human life, should be cheap and almost every where to be had; but now the Egyptians must either drink blood, or die for thirst. Egypt was a pleasant land, but the dead fish and blood now rendered it very unpleasant. It was a righteous plague, and justly sent upon the Egyptians; for Nile, the river of Egypt, was their idol. That creature which we idolize, God justly takes from us, or makes bitter to us. They had stained the river with the blood of the Hebrews' children, and now God made that river all blood. Never any thirsted after blood, but sooner or later they had enough of it. It was a significant plague; Egypt had great dependence upon their river, Zec 14:18; so that in smiting the river, they were warned of the destruction of all the produce of their country. The love of Christ to his disciples changes all their common mercies into spiritual blessings; the anger of God towards his enemies, renders their most valued advantages a curse and a misery to them. Aaron is to summon the plague by smiting the river with his rod. It was done in the sight of Pharaoh and his attendants, for God's true miracles were not performed as Satan's lying wonders; truth seeks no corners. See the almighty power of God. Every creature is that to us which he makes it to be water or blood. See what changes we may meet with in the things of this world; what is always vain, may soon become vexatious. See what mischievous work sin makes. If the things that have been our comforts prove our crosses, we must thank ourselves. It is sin that turns our waters into blood. The plague continued seven days; and in all that time Pharaoh's proud heart would not let him desire Moses to pray for the removal of it. Thus the hypocrites in heart heap up wrath. No wonder that God's anger is not turned away, but that his hand is stretched out still.