Abyss, on 28 October 2015 - 03:03 PM, said:
The tincture against the bloodfly effects was earlier on in the book, it was a brew that Heboric knew about that would drive the larvae out (chapter 6 or thereabouts).
The fountain water simply has a slight regenerative effect. Felisin muses later in the book that after drinking from the water and eating the fruits, "she felt healthier - more mended - than she had in a long time, as if memories no longer bled and she was left with naught but scars."
I think the main reason why SE stresses it is to show Heboric's heightened sensitivity to past events in the area, his new powers providing him with some sort of link to the history of his surroundings. Don't think the effects of the water and fruit ever recur as a storyline element in themselves.