According to John the source of the living water that Jesus talks about is the Holy Spirit (John 7:39). Jesus also declared that He is the light of the world (John 8:12)
I find it interesting that this is not explained any further here in this passage as the symbolism of the water in John 7. No one points it out, but John did describe this though “In Him was life, and the life was the light of men” (John 1:14). Jesus is the Light of Life (John 8:12b) and the Light of the world (John 9:5) and everyone that receives Him (John 1:9) and believes in Him (John 12:46) receives this Light (John 12:35-36) that no darkness can overcome (John 1:5).
The same way we desire the water of the Spirit we should also desire the Light of Life believing in Jesus’ presence and receiving Him wherever we are and in every situation that we may have light.