He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water.
Note 9 at Joh 7:38: This phrase "as the scripture hath said" could be referring to Isa 58:11 where the Lord promised to make us "like a watered garden, and like a spring of water, whose waters fail not." This promise, however, was a promised result of a godly type of fast and was not clearly associated with any aspect of the New Covenant. Jesus' statement would also not be a very close quotation of Isa 58:11 or of Jer 31:12, which contains a similar passage.
It is also possible that this phrase would be referring back to believing on Him, and that would render the meaning of this verse to be, "If we believe on Jesus as the scriptures teach that we should believe on Him, then out of our bellies shall flow rivers of living water."
Note 10 at Joh 7:38: These rivers of living water are referring to the Holy Spirit and the effects He produces in the lives of believers. Ga 5:22-23 says that "the fruit of the Spirit is love, joy, peace, long-suffering, gentleness, goodness, faith, meekness, temperance." These qualities should flow out of us as an artesian well. They should not have to be pumped. They will flow as we conform our thinking to God's Word (Pr 23:7; Isa 26:3; Ro 8:6, and 12:2).