At the Microsoft kitchens, we have these water machines with the typical 'this is not a drain' - do not pour water into the slush tray:
The design of this specific water machine simply has the design affordance for one to think they are hooked up to the water pipes and hence that slush tray, one would think, would work like a sink drain.
Note that the water machines are even inset into the kitchen counter for me to assume that it's hooked up to the water out pipe.
And so I daydream, if only the machine had a visible bottom where one can obviously see that there is no drain in the slush tray (aided by a lighter interior, perhaps even white to psychologically make people afraid about dirtying the nice white interior!). And I suppose the water-in pipe will just have to invisibly be hooked from the back or bottom, ideally at the top of the machine so again users would assume the mental model that it's the in-pipe and not the out-pipe...
Of course ideally, the water machines should be hooked with an out-pipe if not for the extra cost ...
