From NNPTC, I was sent to the Navy's wonderful prototype reactor plants in the middle of a desert... in Idaho... in winter to spend some time learning to operate a nuclear reactor that used to float in a pool of water as a mock submarine. This story was told to me about "controlled pure water" and the abbreviation for it... CPW. Basically, any water that has been through the reactor and then purified to standards 1000 times more stringent than potable water is CPW.
Well, the Navy runs on roughly 3 things at a place like that, with long 12-hour shifts and not too much for entertainment. So we got coffee, telling stories, and standing watch. Well, this one ties in #1 and #2, so hear me out.
The "noobs" or "nubs" of the fleet were often tasked with coffee making and refilling for the slightly more senior folks. Well, as the story goes, a trainee was being questioned about different plant components as part of his testing. It was pretty common to ask trainees questions in unusual ways, to plumb the depth and breadth of their knowledge, so one youngster was asked to explain what CPW was.
"Oh, that's just coffee pot water."
"Yeah, that's funny. No, you need to explain the CPW system."
[Confused look] Well, there's a tap over beside the wall where you can fill the coffee pots.
[Concerned look] Uh, ok, show me where you get the water for the coffee pot.
[Points to CPW system test tap] Right here!
Ok, so I don't really know if this ever happened... but if it did... I'll bet it was quite an incident! The CPW system, just so you know, didn't have any "special" marking on it, so while plausible, it may be apocryphal.