"If any man is thirsty , let him come to me .
Let the man come and drink who believes in me .
As scripture says:“From his breast shall flow fountains of living water.” " (Jerusalem Bible , 1966 edition)
The footnotes to my Jerusalem Bible say that “according to the oldest tradition the living waters flow from Jesus himself . But another tradition has joined “the man who believes in me” with what follows , making the streams flow from the believer .”
The footnote to the USCCB website for this verse reads “From within him: either Jesus or the believer; if Jesus, it continues the Jesus-Moses motif (water from the rock, [Ex 17:6] as well as Jesus as the new temple Grammatically, it goes better with the believer.”