Eunoe is the other water of Eden, the one that restores the memory of every good deed. It works only if Lethe has been tasted first, and the order is forgetting first, remembrance of the good afterward. Matelda leads Dante to it in the last canto, and it is from this bath that he emerges like a renewed plant, pure and ready to rise to the stars.
Where It Appears
Quotes
On this side it descends with the virtue of taking the memory of sin from someone; from the other, it gives back the memory of every good deed. From here, Lethe; so, on the other side, it is called Eunoe, and it does not work unless it has first been tasted on one side and on the other.
Cantos XXVI to XXIX: The fire and Eden, Matelda, to Dante, explaining the two waters of Eden