probably the only thing that Poles and Brits have in common
I wouldn't say the only thing, but your next point is correct.
Without going into the usual 'how to define the UK and its inhabitants' thing, I have had quite a few conversations with Poles about how bad our own countries are, but how the other's is much nicer because blah blah blah. I've had conversations with Germans, only their case is a little different as they usually agree with me about how bad the UK is, whereas I can't say quite so many nice things about Germany.
I have drunk Polish tap water, although if you're recovering from drinking, why not rehydrate yourself with some lovely Polish beer, vodka, or maybe even s******s. On second thoughts, sometimes the tap water might seem like a safer option.