Exodus 7:19

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.

Say unto Aaron, Take thy rod, and stretch out thine hand upon the waters of Egypt. Since Egypt never had but one river, and it is spoken of in the following verse under its ordinary name, Yª`or, in the singular (Genesis 15:18; Isaiah 19:5), the waters enumerated here must have been derivatives from the parent stream. [Wachªrªtaam the natural branches of the Nile in the Delta; yª'oreeyhem (H2975) the canals; 'agmeeyhem (H98), now Birket, ponds, stagnant pools, caused by the superfluous waters in the subsidence of the inundation, in marshy places, where reeds grew; miqweey (H4723) meeymeeyhem (H4325), a gathering of waters, artificial reservoirs, of which a noted specimen was lake Moeris; uwbaa`eetsiym (H6086) uwbaa'ªbaaniym (H68), in vessels of wood and stone.] This was pre-eminently an Egyptian custom. The Nile water, which is the only potable water in the country, is kept for domestic purposes in vessels of wood, more frequently of earthenware or stone, to filter. This is accomplished in a few days; but when necessity requires a more rapid filtration, the process is accelerated by an infusion of bruised almonds. Besides the vessels used for keeping water in private houses, there were stone resevoirs built up at the corners of the streets and in other place, where fresh water was stored for the poor (OEdmann, quoted in Keil and Delitzsch's 'Commentary,' p. 479).