It is written:
“And in that day it shall be—That living waters shall flow from Jerusalem, Half of them toward the eastern sea And half of them toward the western sea; In both summer and winter it shall occur.” (Zechariah 14:8)
From studying the phrase “in that day” as used throughout the Book of Zechariah, it seems evident that “that day” has general reference to the Christian Age, focusing especially on the events preceding the Second Coming of Christ. Please consider the following.
First, there is definite reference made to the Messiah of God (Zechariah 12:10-14; 13:7-9), and this is specifically applied to Jesus during the Christian Age (Revelation 1:7). Second, we are told about the salvation that would be extended to the repentant (Zechariah 13:1), and this began on the Day of Pentecost when the Gospel message was first preached (Acts 2:37-47). Third, God’s people would be persecuted by the nations of the world (Zechariah 12:3, 4, 8), and Jesus Himself reminds us that in the Great Tribulation of the Christian Age all nations would rise up against His people (Matthew 24:9).
All of these facts show us that the phrase “in that day” has specific reference to the times of the Christian Age, i.e., the time of the Messiah’s reign. Indeed, the fact that this is the case was understood by the Jewish people long before the time of Christ, as one author who has carefully researched the Jewish rabbis has thoroughly documented:
“Zech. i. 20 [Then the Lord showed me four craftsmen]. The four carpenters there spoken of are variously interpreted in the Talmud (Sukk. 52 b), and in the Midrash (Bemidbar R. 14). But both agree that one of them refers to the Messiah. Zech. ii. 10 [” Sing for joy and be glad, O daughter of Zion; for behold I am coming and I will dwell in your midst,” declares the Lord] is one of the Messianic passages to which we have referred in our remarks on Is. lx. 4. It has also a Messianic cast in the Targum. Zech. iii. 8 [Now listen, Joshua the high priest, you and your friends who are sitting in front of you—indeed they are men who are a symbol, for behold, I am going to bring in My servant the Branch]. The designation ‘Branch’ is expressly applied to King Messiah in the Targum. Indeed, this is one of the Messiah’s peculiar names. Verse 10 [‘ In that day,’ declares the Lord of hosts, ‘every one of you will invite his neighbor to [sit] under [his] vine and under [his] fig tree.’] is quoted in the Midrash on Ps. lxxii. (ed. Warsh. p. 56 a, at the top) in a description of the future time of universal peace. Zech. iv. 7 [What are you, O great mountain? Before Zerubbabel [you will become] a plain; and he will bring forth the top stone with shouts of “Grace, grace to it!”] is generally applied to the Messiah, expressly in the Targum, and also in several of the Midrashim. Thus, as regards both clauses of it, in Tanchuma (Par. Toledoth 14, ed. Warsh. p. 37 b and 38 a). Verse 10 [For who has despised the day of small things? But these seven will be glad when they see the plumb line in the hand of Zerubbabel—[ these are] the eyes of the Lord which range to and fro throughout the earth] is Messianically explained in Tanchuma (u. s.). Zech. vi. 12 [Then say to him, ‘Thus says the Lord of hosts, “Behold, a man whose name is Branch, for He will branch out from where He is; and He will build the temple of the Lord.'”] is universally admitted to be Messianic. So in the Targum, the Jerusalem Talmud (Ber. 5 a), in the Pirqé de R. Eliez. c. 48, and in the Midrashim. Zech. vii. 13 [” And just as He called and they would not listen, so they called and I would not listen,” says the Lord of hosts] is one of the three passages supposed to mark the near advent of Messiah. See our remarks on Jer. v. 19. Zech. viii. 12 [For [there will be] peace for the seed: the vine will yield its fruit, the land will yield its produce and the heavens will give their dew; and I will cause the remnant of this people to inherit all these [things]] is applied to Messianic times in Ber. R. 12. See our remarks on Gen. ii. 4. Zech. viii. 23 [Thus says the Lord of hosts, ‘In those days ten men from all the nations will grasp the garment of a Jew, saying, “Let us go with you, for we have heard that God is with you.”‘] is one of the predictions expected to be fulfilled in Messianic days, it being however noted that it refers to instruction in the Law in that remarkable passage on Is. lx. 1 in Yalkut ii. p. 56 d, to which we have already referred. In Zech. ix. 1 [The burden of the word of the Lord is against the land of Hadrach, with Damascus as its resting place (for the eyes of men, especially of all the tribes of Israel, are toward the Lord)] the name ‘Chadrakh’ is mystically separated into ‘Chad,’ sharp, and ‘rakh,’ gentle, the Messiah being the one to the Gentiles and the other to the Jews (Siphré on Deut. p. 65 a, Yalkut i. p. 258 b). Verse 9 [Rejoice greatly, O daughter of Zion! Shout [in triumph], O daughter of Jerusalem! Behold, your king is coming to you; He is just and endowed with salvation, Humble, and mounted on a donkey, Even on a colt, the foal of a donkey]. The Messianic application of this verse in all its parts has already repeatedly been indicated. We may here add that there are many traditions about this ass on which the Messiah is to ride; and so firm was the belief in it, that, according to the Talmud, ‘if anyone saw an ass in his dreams, he will see salvation’ (Ber. 56 b). The verse is also Messianically quoted in Sanh. 98 a, in Pirqé de R. Eliez. c. 31, and in several of the Midrashim. On verse 10 [I will cut off the chariot from Ephraim And the horse from Jerusalem; And the bow of war will be cut off. And He will speak peace to the nations; And His dominion will be from sea to sea, And from the River to the ends of the earth] see our remarks on Deut. xx. 10. Zech. x. 4 [From them will come the cornerstone, From them the tent peg, From them the bow of battle, From them every ruler, [all] of them together] is Messianically applied in the Targum. Zech. xi. 12 [I said to them, “If it is good in your sight, give [me] my wages; but if not, never mind!” So they weighed out thirty [shekels] of silver as my wages] is Messianically explained in Ber. R. 98, but with this remark, that the 30 pieces of silver apply to 30 percepts, which the Messiah is to give to Israel. Zech. xii. 10 [I will pour out on the house of David and on the inhabitants of Jerusalem, the Spirit of grace and of supplication, so that they will look on Me whom they have pierced; and they will mourn for Him, as one mourns for an only son, and they will weep bitterly over Him like the bitter weeping over a firstborn] is applied to the Messiah the Son of Joseph in the Talmud (Sukk. 52 a), and so is verse 12 [The land will mourn, every family by itself; the family of the house of David by itself and their wives by themselves; the family of the house of Nathan by itself and their wives by themselves], there being, however, a difference of opinion whether the mourning is caused by the death of the Messiah the Son of Joseph, or else on account of the evil concupiscence (Yetser haRa). Zech. xiv. 2 [For I will gather all the nations against Jerusalem to battle, and the city will be captured, the houses plundered, the women ravished and half of the city exiled, but the rest of the people will not be cut off from the city] will be readily understood to have been applied to the wars of Messianic times, and this in many passages of the Midrashim, as, indeed, are verses 3, 4, 5, and 6 [Then the Lord will go forth and fight against those nations, as when He fights on a day of battle. In that day His feet will stand on the Mount of Olives, which is in front of Jerusalem on the east; and the Mount of Olives will be split in its middle from east to west by a very large valley, so that half of the mountain will move toward the north and the other half toward the south. You will fby the valley of My mountains, for the valley of the mountains will reach to Azel; yes, you will fjust as you fled before the earthquake in the days of Uzziah king of Judah. Then the Lord, my God, will come, [and] all the holy ones with Him! In that day there will be no light; the luminaries will dwindle]. Verse 7 [For it will be a unique day which is known to the Lord, neither day nor night, but it will come about that at evening time there will be light]. The following interesting remark occurs in Yalkut on Ps. cxxxix. 16, 17 [Your eyes have seen my unformed substance; And in Your book were all written The days that were ordained [for me], When as yet there was not one of them. How precious also are Your thoughts to me, O God! How vast is the sum of them!] (vol. ii. p. 129 d) on the words ‘none of them.’ This world is to last 6,000 years; 2,000 years it was waste and desolate, 2,000 years mark the period under the Law, 2,000 years that under the Messiah. And because our sins are increased, they are prolonged. As they are prolonged, and as we make one year in seven a Sabbatic year, so will God in the latter days make one day a Sabbatic year, which day is 1,000 years —to which applies the verse in Zechariah just quoted. See also Pirqé de R. Eliez. c. 28. Verse 8 [And in that day living waters will flow out of Jerusalem, half of them toward the eastern sea and the other half toward the western sea; it will be in summer as well as in winter] is Messianically applied in Ber. R. 48. See our remarks on Gen. xviii 4, 5. Verse 9 [And the Lord will be king over all the earth; in that day the Lord will be [the only] one, and His name [the only] one] is, of course, applied to Messianic times, as in Yalkut i. p. 76 c, 266 a, and vol. ii. p. 33 c, Midr. on Cant. ii. 13, and in other passages.” (Alfred Edersheim and edited by Robert C. Newman, Messianic Passages in the Old Testament as Cited in Rabbinic Literature, 1535-16098 (Kindle Edition); IBRI Occasional Paper #35)
However, it also needs to be pointed out that the phrase “in that day” also sometimes included specific reference to the times near the end of the Christian Age. First, we are told that “in that day” the city of Jerusalem will again be inhabited by Jewish people (Zechariah 12:6). The specific phraseology “inhabited again” after a reference to their devastation and besieging (Zechariah 12:1-2) speaks to a time after the destruction of Jerusalem in 70 A.D. by the Romans (Matthew 24:4-34). Furthermore, the repentance of these Hebrews is hinted at (Zechariah 12:5, 7), as is their deliverance by the Messiah (notice the references to David and the Angel of the Lord, a preincarnate form of Christ-Zechariah 12:8). This began to be fulfilled in 1948 AD (Ezekiel 4:4-6). Second, we are told that the Lord Himself will save His people in that Day when He comes “with His saints,” (Zechariah 14:5). Compare this with the clear statements of 1 Thessalonians 4:13-18 and Jude 14-15, where there is clear reference to the Second Coming of Christ. Third, this specific time of deliverance is known only to the Lord Himself (Zechariah 14:7), when the lights of the Earth diminish (Zechariah 14:6), and when God’s people are besieged by Satan and all his forces (Zechariah 14:4-5). Remember that of the Day of Christs Return, only God Himself knows (Matthew 24:36; Mark 13:32). At that time, God will destroy the as the elements are destroyed (2 Peter 3:10-13) and God’s enemies are punished while His people are saved by Him (2 Thessalonians 1:7-10).
The “living water” would be manifested during the Christian Age, including (but not limited to) the Return of Christ at His Second Coming.