Jesus is not quoting the exact words of any particular passage of scripture, but He is relating the thought of many scriptures such as the following:

Ps 36:8-9  They feast in the abundance of your house; you give them drink from your river of delights.  For with you is the fountain of life; in your light we see light.

Isa 41:17-18  “The poor and needy search for water, but there is none; their tongues are parched with thirst. But I the LORD will answer them; I, the God of Israel, will not forsake them.  I will make rivers flow on barren heights, and springs within the valleys. I will turn the desert into pools of water, and the parched ground into springs.

Isa 43:20  The wild animals honour me, the jackals and the owls, because I provide water in the desert and streams in the wasteland, to give drink to my people, my chosen,

Isa 44:3  For I will pour water on the thirsty land, and streams on the dry ground; I will pour out my Spirit on your offspring, and my blessing on your descendants.

Isa 55:1 “Come, all you who are thirsty, come to the waters; and you who have no money, come, buy and eat! Come, buy wine and milk without money and without cost.

Isa 58:11  The LORD will guide you always; he will satisfy your needs in a sun-scorched land and will strengthen your frame. You will be like a well-watered garden, like a spring whose waters never fail.

Jer 2:13  “My people have committed two sins: They have forsaken me, the spring of living water, and have dug their own cisterns, broken cisterns that cannot hold water.

Eze 47:1  The man brought me back to the entrance of the temple, and I saw water coming out from under the threshold of the temple towards the east (for the temple faced east). The water was coming down from under the south side of the temple, south of the altar.

Joel 3:18  “In that day the mountains will drip new wine, and the hills will flow with milk; all the ravines of Judah will run with water. A fountain will flow out of the LORD’s house and will water the valley of acacias.

Zec 13:1  “On that day a fountain will be opened to the house of David and the inhabitants of Jerusalem, to cleanse them from sin and impurity.

Zec 14:8  On that day living water will flow out from Jerusalem, half to the eastern sea and half to the western sea, in summer and in winter.

Compare coming to Jesus in the preceding verse to believing on Him in this verse. Faith brings us to Christ and to drink is to exercise that faith.

Note the quantity of living water used by Jesus to quench our spiritual thirst. He doesn’t just give a glassful; but an ocean.

Note also that it is out of the believer’s innermost being from which the living water will flow. We who believe on Him become a source to others. In fact, if we do not allow the outpouring of these living waters, we will become like the Dead Sea, which receives the waters of the Jordan River but gives nothing out and thus becomes dead and lifeless. As Bunyan wrote:

“There was a man, the world did think him mad,
The more he gave away, the more he had.”