On the last day of the feast, the great day, Jesus stood up and cried out, “If anyone thirsts, let him come to me and drink. Whoever believes in me, as the Scripture has said, ‘Out of his heart will flow rivers of living water.’” Now this he said about the Spirit, whom those who believed in him were to receive, for as yet the Spirit had not been given, because Jesus was not yet glorified.
Two possible translations:
1) “If anyone thirsts, let him come to me and drink. Whoever believes in me, as the Scripture has said, ‘Out of his heart will flow rivers of living water.’”
The rivers of living water flow out of the believer.
2) “If anyone thirsts, let him come to me, and let him who believes in me drink. As the Scripture has said, ‘Out of his heart will flow rivers of living water.’”
Or, more literally:
“If anyone thirsts, let him come to me,
and let him drink, the one who believes in me.
As the Scripture has said,
‘Out of his heart will flow rivers of living water.’”
The rivers of living water flow out of Jesus.