It's interesting that this was pointed out, as I just recently created a character to play with who is a plumber... in space!! No, really, she's part of Starfleet but someone has to make sure the water goes where it's supposed to go and not where it's not, and that it gets purified correctly and whatnot, especially since water is a finite resource on a starship.

Not that I'm a paid writer or anything; I'm just doing it for fun. :)