Those two examples are bad data points. There is a precise and logical reason in both cases for preferring kitchen water over bathroom water.
Hang on. You're throwing the data out for being too precise and logical? Or am I missing something here?
Nope. I'm discarding data that is relevant to the matter at hand, but does not provide useful input.
See, the hypothesis isn't "Bathroom water is icky because (Object reasons[])".
The hypothesis is "I don't drink bathroom water."
No reasons. In fact, somebody *cough cough* had just put it rather eloquently:
... and at home I simply prefer to not drink bathroom water (call it an odd habit).
The second point there, the HIV research lab, is similar to not drinking bathroom water because of rats or rust in the pipes. Relevant, but not useful.
The first point is not drinking bathroom water because it's an odd habit, simple preference. Relevant and useful.
And my question is about the zeroth point: why is using water for washing/brushing teeth not equivalent to actually drinking it?