On that day: As in verse 6, this represents the longer Hebrew formula, which indicates the beginning of a new paragraph (compare the notes on verse 6). The present paragraph covers verses 8-12. In some languages it will be possible to render this phrase as “On that day it will happen that.” At any rate, On that day should be translated in the same way as in verse 6.
Living waters shall flow out from Jerusalem: The Hebrew idiom living waters means “running water[s]” (Jerusalem Bible, Revised English Bible) or “fresh water” (Good News Translation, New Jewish Publication Society’s Tanakh). It is curious to note that whereas Jerusalem Bible had “running waters,” New Jerusalem Bible has changed to “living waters”; on the other hand New English Bible had “living water,” but Revised English Bible has changed to “running water.” There is no doubt that “running water” is the more natural expression in English. In Hebrew the word for water is normally plural, but in English it is more natural to use the singular. “Running water” (as opposed to still water collected in cisterns) was used for ritual purposes (Lev 14.5). Pictures similar to this one based on “running water” are found in Ezek 47.1-12 and Joel 3.18, but in those passages the water flows only from the Temple. Here it flows from the city more generally (see also Rev 22.1). In some languages the phrases “running water” and shall flow can be combined; for example, “It will happen on that day that water will flow [or, run] from….”
Half of them to the eastern sea and half of them to the western sea: The spring of water originating in Jerusalem will divide into two. One branch will flow eastwards possibly through the newly formed valley of verse 4. It will flow toward the eastern sea, that is “the Dead Sea” (Good News Translation, Contemporary English Version, New Living Translation; compare Bible en français courant, Parola Del Signore: La Bibbia in Lingua Corrente), and the other branch will flow toward the western sea, that is “the Mediterranean [Sea]” (Good News Translation, Contemporary English Version, New Living Translation). In most languages it will be better to use the terms by which these seas are known today than to keep the obscure terms eastern sea and western sea. At the very least the modern names should be supplied in footnotes, as in New International Version, New Jewish Publication Society’s Tanakh, and Traduction œcuménique de la Bible. These terms form a contrasting pair only here and in Joel 2.20. The terms used for eastern and western here are different from those in the middle of verse 4, and carry the idea of “in front” and “behind.” Again the assumption is that the speaker stands facing east. The meaning is the same here as in verse 4 and translators do not need to look for different terminology for the directions in their translation.
The description here shows a wider concept of the LORD’s blessing in the end time than that found in Ezek 47.1-12, where all the water coming from the Temple flows eastward to the Dead Sea. The text here may intend readers to make a mental comparison with the river of Eden, which divided into four (Gen 2.10-14).
It shall continue in summer as in winter: In the Holy Land rain falls only during the winter months, with the result that many streams are seasonal, and dry up during the hot summer months. A never failing supply of fresh water is a striking symbol of blessing to people who live in such conditions. In many parts of the world, the meaning will be expressed more clearly by saying “in the dry season as well as the wet” (Good News Translation, Bible en français courant, Die Bibel im heutigen Deutsch, 1. Edition, Parola Del Signore: La Bibbia in Lingua Corrente).
Quoted with permission from Clark, David J. & Hatton, Howard A. A Handbook on Zechariah. (UBS Helps for Translators). New York: UBS, 2002. For this and other handbooks for translators see here .