“In the last day, that great day of the feast, Jesus stood and cried, saying, If any man thirst, let him come unto me, and drink.”
King James Version (KJV)
7:37 On the last, the great day of the feast - On this day there was the greatest concourse of people, and they were then wont to fetch water from the fountain of Siloam, which the priests poured out on the great altar, singing one to an other, With joy shall ye draw water from the wells of salvation. On this day likewise they commemorated God's miraculously giving water out of the rock, and offered up solemn prayers for seasonable rains.
Joh 7:37 In the last day. Probably the eighth day, possibly the seventh. The eighth was a day of holy rest added to the seven days of the feast. If any man thirsteth, let him, etc. Jewish writers say that water was brought every day of the feast in a golden pitcher from the pool of Siloam and poured upon the altar. It is thought that it was when this water was poured out that Jesus cried out, and pointed to the living water.