This verse probably comes from the “Priestly” source, for here Aaron becomes the designated agent rather than Moses. (Scholars believe verses 14-18 probably came from the “J” or “Yahwist” source. See the discussion on “Sources” in “Translating Exodus,” page 2.) Verses 16-18 were to be spoken by Moses to the Pharaoh, but now verse 19 is to be spoken to Aaron. The LORD said to Moses introduces the words spoken to Moses, who in turn is to Say to Aaron the words of the quote within a quote.

Take your rod is spoken to Aaron, so it is Aaron’s rod that is to be used. (See verse 9.) Stretch out your hand probably refers to the hand in which Aaron holds the rod. So Good News Translation‘s interpretation of this double command is correct: “Tell Aaron to take his stick and hold it out.” Over the waters of Egypt refers to all bodies of water throughout the land of Egypt. This is to be, of course, a symbolic gesture which would add drama and suspense. Some translations omit over the waters of Egypt as redundant, since all the bodies of water are listed after this statement. Good News Translation shows this with the word “all” before the list.

Their rivers may be understood as “its rivers” (New English Bible, New Jewish Publication Society’s Tanakh), meaning Egypt’s rivers. The pronoun there is plural because the Hebrew word for Egypt is plural in form and can mean either the land (Egypt) or the people (Egyptians). In most languages it will be more natural style simply to say “the rivers” (Good News Translation), as it will be understood that the rivers are in Egypt. The word for rivers refers to a permanent watercourse. The word for canals refers here to streams or tributaries flowing into the Nile as well as irrigation ditches from the Nile.

Ponds were low, swampy areas that were full of reeds. (Jerusalem Bible and New Jerusalem Bible translate “marshland.”) And the word for pools refers to any accumulation of water. Good News Translation reduces the four terms to three, taking pools of water as a general reference to the other three. (New Jewish Publication Society’s Tanakh has “bodies of water.”)

That they may become blood is literally “and they will be [or become] blood.” The clause may be understood as stating the purpose of Aaron’s dramatic act (“in order that they will become blood”) or the result (“and then they will become blood”). (See verse 17 and the comment.) By punctuation New International Version removes this clause from the words of Moses to Aaron and considers it to be only the LORD’s words to Moses. This is implied in Good News Translation, which uses indirect discourse for Moses’ words to Aaron and begins a new sentence with this clause.

Revised Standard Version and others consider this to be still part of Moses’ words to Aaron, but in New International Version, tot, and Good News Translation it is better understood as the LORD’s explanation to Moses. (See the comment at 19a, first paragraph.) And there shall be blood is literally “blood will be.” Throughout all the land of Egypt includes the entire country.

Vessels of wood and vessels of stone is an interpretation of the Hebrew, which only says “and in the trees and in the stones.” It is not clear what is meant. Some translations have avoided adding the idea of vessels, such as Translator’s Old Testament (“even on the trees and stones”) and New Jerusalem Bible (“even in sticks and stones”). It is possible that trees with sap and rocks with springs are intended. Most translations, however, supply suitable words as in Good News Translation, “even in the wooden tubs and stone jars,” or in Contemporary English Version, “and even the water in buckets and jars.” Following Good News Translation, therefore, translators need to identify two kinds of water containers, one made of wood and the other of clay or stone—if these two types are available in the receptor language. If not, it will be possible to combine the two and translate “even in vessels used for storing water.”

Quoted with permission from Osborn, Noel D. and Hatton, Howard A. A Handbook on Exodus. (UBS Helps for Translators). New York: UBS, 1999. For this and other handbooks for translators see here .