Living water is what comes from a spring or fountain bubbling up from underneath the ground. It is not water collected in a cistern. When we were in Israel, we saw a huge cistern on two levels that was at Masada that collected rainwater from the mountains and contained thousands of gallons of water. There was enough water to allow over 900 people to last for over two years in the siege of the Romans against them. But it was still a cistern, not living water.
Jeremiah 2:13 KJV
For my people have committed two evils; they have forsaken me the fountain of living waters, and hewed them out cisterns, broken cisterns, that can hold no water.
Jeremiah is listing the contrast between a fountain of “living waters” and a cistern. And he also states that when a cistern is broken, then it is even worse. It cannot hold any water. The Lord is the fountain of living water.
Jeremiah 17:13 KJV
O LORD, the hope of Israel, all that forsake thee shall be ashamed, and they that depart from me shall be written in the earth, because they have forsaken the LORD, the fountain of living waters.
Jesus had a discussion with a Samaritan woman at a well in John 4 where he teaches the concept of living water.
John 4:7-11 APNT
And a woman from Samaria came to draw water. And Jesus said to her, “Give me water to drink,”
for his disciples had entered the city to buy food for them.
That Samaritan woman said to him, “How is it [since] you are a Judean, yet you ask to drink of me, who am a Samaritan woman? For the Judeans do not deal with the Samaritans.”
Jesus answered and said to her, “If you were aware of the gift of God and who this is who said to you, ‘Give me to drink,’ you would ask him and he would give you living water.”
That woman said to him, “My Lord, you have no water pot and the well is deep. Where [is] your living water?
Jesus is saying to the woman that he is the source of living water and it will be in the person.
John 4:12-15 APNT
Are you greater than our father Jacob, who gave us this well and from which he and his sons and his flocks drank?”
Jesus answered and said to her, “Everyone who drinks from this water will thirst again,
but everyone who drinks from the water that I give him will not thirst forever. But that water that I give him will be in him a spring of water that will bubble up to eternal life.”
That woman said to him, “My Lord, give to me from this water, so that I will not thirst again nor have to come [and] draw [water] from here.”
The Samaritan woman is starting to get the idea of what he is talking about because eventually she realizes that he is the Messiah. We need to understand two points here. The living water bubbles up to eternal life and whoever drinks it will not thirst again.
Now we will read what happened at the Feast of Tabernacles.
John 7:37-38 APNT
And on the high day, which is the last [day] of the feast, Jesus was standing and he cried out and said, “If anyone is thirsty, he should come to me and drink.
Whoever believes in me, as the scriptures have said, rivers of living water will flow from his inner part.”
On each day of the Feast of Tabernacles, the priests practiced a tradition called the water pouring. While the morning sacrifice was being prepared, a priest, accompanied by a joyous procession with music, went down to the Pool of Siloam (which was fed by the Gihon Spring). They would draw water into a golden pitcher and then make a procession back to the temple. When they entered by the “Water-gate” there was a threefold blast of trumpets. Then the water was poured out into basins beside the altar.
As soon as the wine offering and the water was poured out, the temple choir and singers began to sing the “Hallel” which was the section of praise psalms from Psalm 113-118. It was a great production each day! One of the verses in these Psalms celebrates the time when God caused water to come out of the rock.
Psalm 114:7-8 KJV
Tremble, thou earth, at the presence of the Lord, at the presence of the God of Jacob;
Which turned the rock into a standing water, the flint into a fountain of waters.
The last verses of Psalm 118 are about the salvation that was promised to Israel.
Psalm 118:21-26 KJV
I will praise thee: for thou hast heard me, and art become my salvation.
The stone which the builders refused is become the head stone of the corner.
This is the LORD'S doing; it is marvellous in our eyes.
This is the day which the LORD hath made; we will rejoice and be glad in it.
Save now, I beseech thee, O LORD: O LORD, I beseech thee, send now prosperity.
Blessed be he that cometh in the name of the LORD: we have blessed you out of the house of the LORD.
At the height of this ceremony, Jesus stood up in the temple and shouted: “Come to me and drink.” Then he quotes a scripture passage that says, “out of his belly shall flow rivers of living water.” There is no specific scripture in the Old Testament which says this about the belly. There are several scriptures that Jesus might have had in mind, all of which refer to something that will happen after he comes back.
Joel 3:18 ESV
And in that day the mountains shall drip sweet wine, and the hills shall flow with milk, and all the streambeds of Judah shall flow with water; and a fountain shall come forth from the house of the LORD and water the Valley of Shittim.
There is a description in Zechariah 14 (which was also read during this particular feast) that tells what will happen in the future when Jesus comes back to the Mount of Olives.
Zechariah 14:3-7 KJV
Then shall the LORD go forth, and fight against those nations, as when he fought in the day of battle.
And his feet shall stand in that day upon the mount of Olives, which is before Jerusalem on the east, and the mount of Olives shall cleave in the midst thereof toward the east and toward the west, and there shall be a very great valley; and half of the mountain shall remove toward the north, and half of it toward the south.
And ye shall flee to the valley of the mountains; for the valley of the mountains shall reach unto Azal: yea, ye shall flee, like as ye fled from before the earthquake in the days of Uzziah king of Judah: and the LORD my God shall come, and all the saints with thee.
And it shall come to pass in that day, that the light shall not be clear, nor dark:
But it shall be one day which shall be known to the LORD, not day, nor night: but it shall come to pass, that at evening time it shall be light.
At the height of the last battle, Jesus’ feet touch the top of the Mount of Olives and the whole mountain is split from east to west.
Zechariah 14:8-9 KJV
And it shall be in that day, that living waters shall go out from Jerusalem; half of them toward the former sea, and half of them toward the hinder sea: in summer and in winter shall it be.
And the LORD shall be king over all the earth: in that day shall there be one LORD, and his name one.
From the split in the mountain, living waters or a great bubbling spring gushes out and flows until it waters the land all the way west to the Mediterranean Sea and east to the Dead Sea. It heals the Dead Sea until it becomes filled with fish.
Ezekiel 47:8-9 KJV
And he said to me, “This water flows toward the eastern region and goes down into the Arabah, and enters the sea; when the water flows into the sea, the water will become fresh.
And wherever the river goes, every living creature that swarms will live, and there will be very many fish. For this water goes there, that the waters of the sea may become fresh; so everything will live where the river goes.”
So now we can go back to John 7 and see that there is an ellipsis in verse 38. “Whoever believes in me, as the scriptures have said [concerning Jerusalem, so will it be that], rivers of living water will flow from his inner part.” The closest verse to this is Zechariah 14:8: “living waters shall go out from Jerusalem.”
Jesus was also prophesying about the Spirit that would come and compared it to water flowing out of the mountains of Jerusalem. Just as the spring of water would come from the middle of the mountain, out of a person’s inner being would flow living water, so that he would not thirst anymore. The word “belly” means inner part in both Greek and Aramaic.
This living water comes from the Spirit that resides in each believer in Christ.
John 7:39 APNT
Now he said this about the Spirit that those who believed in him were about to receive, for the Spirit was not yet given, because Jesus was not yet glorified.
Rivers of living water will flow from the inside, not from man-made rules and regulations or our human minds. Mankind always needs water to live. So, he always needs the insight of the spiritual water that comes from God by way of Jesus Christ. That is why we don’t ever need to thirst. We can always have spiritual answers to the deepest needs in our lives. We can draw water out of the fountain of deliverance.
Isaiah 12:2-3 NET
Look, God is my deliverer! I will trust in him and not fear. For the LORD gives me strength and protects me; he has become my deliverer.
Joyfully you will draw water from the springs of deliverance.
The Lord is the fountain of living waters and just as the water will heal the land in the end times, so this spiritual flow heals all of the “dead” stuff in our lives. What answers of spiritual water do you need today? Jesus says, “Come and drink of me.”
 Edersheim, Alfred. The Temple, pp. 241-244.