Forgetting the fact that in fact it does happen, I can say with 100 percent certainty that I have personally witnessed it. So using that as a barometer, including verbatim the conversation that I personally witnessed and quoted above, I cannot imagine that I have been on the only flight that this has ever happened on - and ignoring the fact that despite whatever certain people think, the water from "approved" places is not as pure as you or BA would wish it to be, or certainly not properly tested. Do you "smiles in the aisles" honestly drink the tank water, based on your handle, I would assume no, as no BA crew members (or on any other carrier that I know) ever drink the tank water. Again, no serious airline serves or advocates that its passengers drink tank water (yes again, other than in coffee or tea...said again to head off the inevitable person who will cite that)