What Is Living Water?

What exactly is Living Water? In John 4:1-26, we see the first mention of living water in the New Testament where Jesus met the Samarian woman at the well:

Jesus answered her, "If you knew the gift of God and who it is that asks you for a drink, you would have asked him and he would have given you living water."
John 4:10 (NIV)

Jesus answered, "Everyone who drinks this water will be thirsty again, but whoever drinks the water I give him will never thirst. Indeed, the water I give him will become in him a spring of water welling up to eternal life."
John 4:13-14 (NIV)

Jesus is referring to eternal life by believing in Him. He is stating that living water is a gift that that would satisfy her soul and is only available through Him. He is offering the joy of eternal life that is available through Jesus Christ. Jesus speaks about living water again in chapter 7 of book of John:

On the last and greatest day of the Feast, Jesus stood and said in a loud voice, "If anyone is thirsty, let him come to me and drink. Whoever believes in me, as the Scripture has said, streams of living water will flow from within him." By this he meant the Spirit, whom those who believed in him were later to receive. Up to that time the Spirit had not been given, since Jesus had not yet been glorified.
John 7:37-39 (NIV)

There are some references to living water in the Bible as the Holy Spirit, which was bestowed upon believers in Acts 10:44-45. That still points back to Jesus via the Holy Trinity (Father, Son, Holy Spirit).

He said to me: "It is done. I am the Alpha and the Omega, the Beginning and the End. To him who is thirsty I will give to drink without cost from the spring of the water of life.
Revelation 21:6 (NIV)

Then the angel showed me the river of the water of life, bright as crystal, flowing from the throne of God and of the Lamb.
Revelation 22:1 (NIV)

From the previous scriptures in the last book of the Bible (Revelation) we can see how crucial it is to have accepted Jesus Christ as our Lord and Savior and thus, have "Living Water" running through us.