Robert Hunter and Jerry Garcia must have been inspired by a supernatural sphere when singing about living water: "a fountain ... not made by the hands of men."
This song may be catchy partly because it relates to a deep level of the soul: the initial separation from the field of unity. On the way back we may be confronted with wounds from the past.
Oh Sister, like many Dylan songs, can be interpreted on various levels: a relationship of siblings, a love affair, possibly with biographical references? From a spiritual perspective, it may be the spirit aspect addressing the soul aspect in man.