Yes, I do have a science background, which is why I love thinking about how a cup of water is full of molecules :)

Speaking only for myself, I understand that 'water' might not be a countable noun, but that doesn't make the underlying thing we call "water" uncountable as a real, tangible thing, and that was what I was trying to convey.

It seems like people might reasonably disagree about whether something is physically countable or not, but it was deeper than linguistics for me.

You might appreciate this: although a lot of scientists don't like people calling insects "bugs," I love how so many languages have a word for "small creepy-crawly animal" and I highly endorse the popular usage of bugs to include spiders, roly-polies, insects, etc. For this, I don't get why some biologists insist on applying the specialist description of living things to the semantic (?) grouping. Maybe you would put 'countable' in that category too. But to me, the idea that water is molecules makes it countable at a deep level, regardless of how our language talks about it.

I'm going to look up and learn more about countable/mass nouns now -- sorry to start out as part of that annoying group. Thanks for the thread :)