We already have to make him buy filters, or he "forgets". The thing is fairly large and already takes up about half a shelf in the fridge, it wouldn't really be feasible, nor would it stop him.
He pulled a brand match on the mayo "Oops, sorry, didn't mean to use yours". I've never found that gambit particularly clever, nor did it pay off. There were only about two sandwiches of mayo left in that bottle, so I bought the olive oil type. (He says that the olive oil type is for hippies.)
Unfortunately, these small transgressions are endemic to shared living spaces. At least he doesn't try to tell me I can't cook meat. That one was a real winner.
For reference, when she moved in, I asked if the meat thing would be a problem, she said it would not be.
Yeah, fishy water would be full of nastiness. probably be cool looking though, and going by bricks post, that's pretty much their natural habitat.