Charles H. Spurgeon on Psalms 105:29

He turned their waters into blood. By the miraculous change of the waters into blood, a practical rebuke was given to their superstitious. This sacred and beautiful river, the benefactor and preserver of the country, this birthplace of their chief gods, this abode of their lesser deities, this source of all their prosperity, this centre of all their devotion, is turned to blood: the waters stink; the canals and pools, the vessels of wood and vessels of stone, which were replenished from the river, all are alike polluted. The Nile, according to Pliny, was the "only source from whence the Egyptians obtained water for drinking" (Hist. Nat. 76, c. 33). This water was considered particularly sweet and refreshing; so much so that the people were in the habit of provoking thirst in order that they might partake more freely of its soft and pleasant draughts. Now it was become abominable to them, and they loathed to drink of it. Thomas S. Millington.