What I loved most about this story was the fatherly bond that developed between the nixie and Sylvain, culminating in the rescue from the fountain. The image of Sylvain cradling and rocking the nixie back to calm resonated with me as a father.
The idea of providing running water through velvet sleeves and magic is genius, and made me realise that the first plumbers must really have been making things up as they went along.
Finally, I loved the image of collapsing all the palatial plumbing both to spite the courtiers and to care for the nixie. It is, for some reason, tremendously satisfying to think of rich layabouts having everything taken from them when they do not appreciate it.
Mokalus of Borg
PS - I'm not clear on what killed Leblanc.
PPS - Though I suppose the detail didn't matter to the story.