The phrase On that day opens a new subparagraph covering just this one verse. As discussed in the notes at the beginning of chapter 12, we recommend that there should not be any section heading here.

There shall be a fountain opened: The phrase shall be … opened is not a simple verb form but a form of the verb “to be” plus a participle. The effect of this construction is to indicate not a single act of opening but rather a continuous state in which the fountain once opened remains so constantly. English versions generally fail to convey this idea. Probably the one that comes nearest is Knox with “a fountain flowing openly,” though this does not sound very natural. Possible models are “there will be a fountain that stays open” and “a fountain will spring up” (Traduction œcuménique de la Bible, Bible en français courant, Die Bibel im heutigen Deutsch, Parola Del Signore: La Bibbia in Lingua Corrente). Some languages do not have a technical term for a fountain. In fact, the very word fountain is somewhat misleading in modern English, even though it is used by all available English versions. Its primary meaning today is an artificial device, often decorative, that shoots water into the air. The required meaning in this context, however, is a natural spring of water, and words meaning “spring” are used in French, German, Italian, Norwegian, and Swedish versions. These provide a better model, so translators may say, for example, “water will pour out of the ground” or “there will be a spring available.”

For the house of David and the inhabitants of Jerusalem: The same phrase occurred in 12.7, 8, 10, and 12. Here, as in 12.7 and 10, it probably means “the rulers and people of Jerusalem.” See the notes on those verses.

To cleanse them from sin and uncleanness: The idea of water being used to make people clean from defilement is an ancient one (see Num 8.7; Num 19.9; Ezek 36.25). The word used for sin is a very general one. The word translated uncleanness is particularly associated with ritual impurity arising from menstruation (Lev 15.19; Ezek 18.6; Ezek 22.10; Ezek 36.17) or from contact with a dead body (Num 19.11-13). In Ezek 36.17-18, the word is linked with idolatrous worship, and that sense is probably present here also. Good News Translation translates it as “idolatry” (Parola Del Signore: La Bibbia in Lingua Corrente also). The overall effect is that the waters of the spring (or, fountain) will cleanse the leaders and people both morally and ritually. “Idolatry” may also be expressed as “worship of the images of false gods.”

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 .