John 4.12-13:
(12) “Are you greater than our father Jacob? He gave us the well and drank from it himself, as did his sons and his livestock.” Jesus said to her, “Everyone who drinks of this water will be thirsty again, (14) but whoever drinks of the water that I give him will never be thirsty again. The water that I will give him will become in him a spring of water welling up to eternal life.” (ESV)
In the verses above Jesus is continuing to transition this conversation with the woman of Samaria from the need of actual water to the issue of spiritual and eternal life. In verse 12 the woman is conversing on the basis that what Jesus is saying is related to physical water. But Jesus gives the explanation that eternal life is the result of drinking “living water”. Jeremiah 17.13 says, “those who turn away from you shall be written in the earth, for they have forsaken the Lord, the fountain of living water.” (ESV) So in effect Jesus is using the same figurative language of “living water” that Jeremiah used to say that the woman of Samaria can receive from Jesus the eternal life that can only come from God.
The symbolism of living water during the time of the Bible was related to purity and its power to make something or someone clean and living. So Jesus is offering to the Samaritan woman God’s gift of eternal life. Since Jesus is communicating the idea that he is the one who would give her this living water, it follows that he is also telling her that he is the Messiah. The expression “spring of water welling up to eternal life” (ESV) is the same idea of the verse of Jeremiah quoted above, and it has its fulfillment in the teaching of 1 Corinthians, chapter 6 that the Holy Spirit of God Himself lives in the body of a believer in Jesus.