I'll think about it. The problem is, I don't have a clear idea of what fantasy sewers should look like. I agree that the water should be treated differently there.
The setting I run is a modern steampunk, so the sewers I run in seem like a strange mix between modern sewer and Victorian brickwork sewers. I lay them out as long, wide tunnels with water channels in the center of walkways with small little maintenance rooms or pump rooms. Dead ends leading to ladder hatches are also a thing I do. (If only because I don't want ladders every short length of tunnel.) Important thing I do, too, is make the tunnels run to the edges of the map implying they continue (if my players want to skip through the water longer, for some reason).
I appreciate the consideration, no matter what you do!