I think it could also be related to Czech Republic being the #1 country in terms of beer consumption per capita [1]. It's definitely a national drink there.
[1]: https://en.wikipedia.org/wiki/List_of_countries_by_beer_cons...
[1]: https://en.wikipedia.org/wiki/List_of_countries_by_beer_cons...
Actual alcohol consumption is not that high. But yes, in pub water is often more expensive than beer.