In Civ6, what are the full rules (including any undocumented ones) for where aqueducts can be placed?
See the below screenshot. It seems like I should be able to place an aqueduct between the city and the river/mountain. Ignore the tooltip which is for a different square.
It has all of the requirements: It is next to the city center, and it is next to a source of fresh water. Two, in fact, since if you look closely there's also a river behind the mountain. When I hover over the square the tooltip also acknowledges that that square is next to a river. And yet, I cannot build an aqueduct because no suitable locations for it can be found.
I saw some comments on Reddit about the same water source not being usable twice, and while I haven't verified that, it also isn't applicable in this case either.