Taking a break from my essay endspurt and re-watching the episode.
Earlier in the post (or maybe another) we discussed over what could come back by Emma drinking the water. We speculated about memories, etc. We overlooked the obvious: just after her drink with August, she finds Henry’s book! Of course it’s really given to her by August, but she doesn’t know that. When she gives the book back to Henry and he asks her how she got it and she explains it to him, he wonders that it’s strange. Her answer: “What other explanation is there?” The look on her face and the intonation of how she delivers the line, seem as if she’s thinking about what August told her about the water. For August to give her back the book immediately after having her drink from the “magic” water, thus is to make her believe in magic, just as someone posted earlier here.
Ok, just looked back on the posts here. It seems the whole water theory is somewhere else, but I can’t find it right now, sorry.