Wandering around in Riverwood I noticed the water trough in the Smithing area has motionless water in it. But identical drinking troughs elsewhere in town have normal moving water in it! Is this a bug, or yet another thing for modders to improve?

Depends how Bethesda did the mesh, either using a static water texture or set is as a water property. It's static in Riverwood for me too so don't worry.

I've only been in Riverwood, so I don't know if all Smithy areas have the same static water? Really weird they use a static water texture in one place, and ten feet away it's dynamic. Inconsistency everywhere. Sigh.