What is the Fountain of Living Water?
The "Fountain of Living Waters" is a reference to the HOLY SPIRIT who dwells within all believers. He was available to believers of the Old Testament dispensation (Jeremiah 2.13; 17.13). He would come and go to enable certain individuals to perform certain tasks.
Examples are found in the lives of David (Psalm 51.11), John the Baptist (Luke 1.80) and Simeon (Luke 2.25-32). In the New Testament dispensation the HOLY SPIRIT is given to all believers in Jesus the Messiah (1 Corinthians 3.16; 6.19; 2 Corinthians 6.16; Ephesians 2.21; James 4.5) and He is referred to by Jesus as a "fountain of water springing up to eternal life" (John 4.14) and "rivers of living water" (John 7.38-39).
An angel told John that those who died for their faith during the Tribulation would have the privilege of drinking from the "Living Fountains of Waters" (Revelation 7.17). It is also called the "River of the Water of Life" (Revelation 22.1). The promise of being able to drink from the "Water of Life" is also given in the fifth to the last verse in the Bible (Revelation 22.17).
The "fountain of living waters" is also a reference to God (Jeremiah 2.13; 7.13). The use of this to refer to the HOLY SPIRIT is just one of dozens of proofs that the HOLY SPIRIT is a member of the Trinity and not just a force.