During the time of Jesus, the tradition of the water libation offering had developed. While this was a tradition and not something God had commanded. Jesus used the occasion to tell the people who He was.
Thanking God for Water During an Offering
The land of Israel has an arid climate and rain is important for growing of crops. At the time of the Feast of Tabernacles, a tradition had developed to ask God to provide rain for the next season. This tradition also pictured the spiritual need of humans to have their souls watered by God.
Each day of the Feast a priest would take a golden pitcher to the pool of Siloam. He would be followed by worshippers with palm branches chanting the Hallel Psalms, Psalm 113 -118. The priest would fill the pitcher with water at the pool and then return to the Temple along with the worshippers. At the Temple, on the altar, the priest would pour out the water while praying for God to provide what only God could provide.
Jesus adds to the Water Libation Offering
Jesus was a Jew and as such celebrated the Feast Days that God had given. Jesus was a controversial figure; some saw Him as Messiah while many other doubted Him. By His third year of ministry the Pharisees led open opposition to Him. At this time, Jesus went to the Temple in the middle of the celebration of Tabernacles. There, amid controversy, He taught at the Temple. Many wondered if He was the Messiah.
On the last day of the Feast, when the water had been poured on the altar, Jesus made a usual announcement. John 7: 37 On the last day, the climax of the festival, Jesus stood and shouted to the crowds, “Anyone who is thirsty may come to me! 38 Anyone who believes in me may come and drink! For the Scriptures declare, ‘Rivers of living water will flow from his heart.’” 39 When he said “living water,” he was speaking of the Spirit, who would be given to everyone believing in him. But the Spirit had not yet been given, because Jesus had not yet entered into his glory.
Division at Announcement
At this many believed that Jesus was the Messiah, but the Pharisees sent the Temple guards to arrest Jesus. John 7: 45 When the Temple guards returned without having arrested Jesus, the leading priests and Pharisees demanded, “Why didn’t you bring him in?”
46 “We have never heard anyone speak like this!” the guards responded.
47 “Have you been led astray, too?” the Pharisees mocked. We can see that the water libation offering was a chance for Jesus to tell the crowd He was the Messiah even though many still would not believe. To hear more listen here: