"I guess it would be hard to clean things effectively, without poisoning the water....." If he thinks about it as if Jade's family really only cleaned things, he actually could see the argument to be made that it's difficult, specialized work. You can't simply dump out a dirty washbasin when you're done with it--any chemicals you use to clean underwater, you're surely forced to breathe in, as well.

That admission is enough to make his heart skip a beat, though he can't quite tell if it's in a good or bad way. Does that mean Jade is thinking about it? Does he already have someone in mind? Maybe that's why he's so steadfastly ignoring his cues, so difficult to impress..... "So soon? You haven't even graduated yet....."