In reply to James Malloch:
I live in the Czech Republic and would have absolutely no qualms about drinking tap water in Prague or nearly anywhere else in the CR either.
The only place I have had a reservation is at our country house which has a private water supply from a spring but there are other houses nearby that have shit tanks and I just know some of them will be poorly maintained. I've never actually had a problem or heard of one but it appears there is a risk. Our neighbour has drank from this supply for 40 years with no problem and laughed when I mentioned it to him, so it's probably a groundless fear.
Now, drinking cheap spirits in the CR is an altogether more risky activity!