In Prague restaurants, mineral water costs more than the same amount of beer. Currently that’s only a few Kč difference, but still astonishing if you consider the complex manufacturing process of beer.
Usually you don’t notice it immediately because beer is mostly sold in units of 0.5l (called a “big” beer – Bavarians would expect a litre and call this here a “half”) while mineral water comes in tiny bottles of 0.25l.
Tap water is only served in some cafés and only in addition to coffee. So if you are thirsty and have to save money, you simply end up with a beer.
Read more about the Czechs’ special relationship to beer in the hilarious book The Czechs in a Nutshell (Review). If you want to learn more about the long-term damages caused by extensive exposure to Czech beer even after your return to your home environment, watch the film Rex-Patriates.