Aaron had scarcely executed the Divine bidding, when all the water of Egypt became blood, even such as was kept in vessels of wood and in vessels of stone. The very spittle of an Egyptian turned into blood no sooner had he ejected it from his mouth, and blood dripped also from the idols of the Egyptians.
The transformation of the waters into blood was intended mainly as a punishment for the oppressors, but it was at the same time a source of profit for the oppressed. It gave the Israelites the opportunity of amassing great wealth. The Egyptians paid them large sums for their water, for if an Egyptian and an Israelite drew water from the same trough, the portion carried off by the Egyptian was bound to be useless, it turned into blood. To be sure, nothing helped the Egyptians in their distress, for though they drank water from the same cup as an Israelite, it became blood in their mouth.