At a typical local pub, a pint—500 milliliters, actually, in this metric-measuring country—costs about $1. A similar portion of water, juice or soda generally costs twice as much. Offering free tap water as at U.S. eateries is extremely rare.
At U Zelenku, a neighborhood institution for more than a century, for instance, a pint of the cheapest beer goes for 99 cents. The same size of soda water is $1.30. At the fancier Kolkovna restaurant in touristy Old Town, a pint is $2.50, while mineral water is $2.29, for a bottle less than half the size.
Here is more. The Czech government may end up mandating that some non-alcoholic drinks be cheaper than beer.
For the pointer I thank Daniel Klein and also NB.