I know, this idea is way out there, and may not stay true to the Haven & Hearth theme, but a water irrigation system would be awesome.
With the recent implementation of the Road Building feature, I think this idea is even more probable.
This system would involve irrigating homes via a well or river water source with clay pipes.
Pipes would be built and then connected similar to a wall and then lead to a main "system" in the center of the town, that would then spider web out to the individuals homes.
The question whether it should be above/below ground up to the devs, but above ground seems the most probable.