True, but it's unlikely to be contaminated.
Just as tap water. It's controlled and tested. And I would never drink e.g. Kropla Beskidu, or former Bonaqa but would not have doubts to drink most tap water. Never got sick after tap water.
Er...and you doubt him/her? Why would he/she lie to you?
Often it's just some unbiased prejudice that "tpa water isn't safe". It used to be like that but it was many years ago.
What the hell would you know about the tap water in Gdańsk?
Well, even I can check it online from Krakow. There are often tests published. Here it says something about water in Gdansk being one of the best in Poland:
i hope this clears out the superstitions about "contaminated" or "unhealthy" tap water. The only thing might be different taste, some people may not like it, depends on region.