Maybe, just maybe, the damage of Water Poisoning could be reduced by a large chunk for every God Soul one has interacted with, in addition to whichever other changes are made? Give a little more purpose to collecting all of Athena’s Pages, and any other future God Soul Sidequests that have relatively little effect for non-Oracles.
The idea of Water Poisoning being something of a brief alert triggered by the presence of certain beings (or fragments thereof) also seems interesting, though it being caused by traces of the divine in the Dark Sea feels… off, to me.