I have been searching throughout the Shadow City of the Sunspear in Westeroscraft for weeks now and still have yet to find the next clue. I have read the books and watched the show and do not believe there is any reference to this in either. I have taken into account that the Water Gardens may also be a possibility but did not find anything there either. While scouring the internet for answers, I also came across the possibility that somewhere in King's Landing may also be called the Shadow City, but have yet to find anything to back that up. If you have perhaps completed the scavenger hunt, it would be really helpful if you could tell me where (more specifically) to search or at least if I'm on the right track.
I have a suspicion that the sign which contains the clue was either removed someone with the ability to build on the server, or was never put up as an error of the individual(s) who designed the scavenger hunt.
My only reasoning for this speculation is this: While the Water Gardens did make sense for this clue, I have searched it high and low (even in hidden and incomplete areas) and found nothing. While searching the Shadow City, I came across a small building called the Public Baths which also contained nothing. The only remaining possibility is the port of the Sunspear, which (you guessed it) contained nothing.
I do not know what happened to the sign, or if I'm just missing it somewhere obvious. All I do know is that I read the books, I watched the show and nowhere does either reference any water other than the places which I have fully searched (the exception is the public baths, which do not appear in either).
My recommendation to anyone attempting to complete this hunt in the future is to give up. Or you could always risk getting booted from the server for revealing this clue when asking for help. Either way, I see no point in proceeding further with this. That is, unless someone has found the next clue in an impossible location and would care to share it.