The first thing to point out is that in our culture, the water, which is served in restaraurants, is invariably mineral water. It is usually served in small bottles. That means that it has to be collected, stored, transported and distributed, which all costs money. The restaurants pass on that expense.
Because I am able to consume very little beer without severe damage, I usually need to drink equal measures of water. When I ask for a large glass of tap water in most pubs - let alone restaurants, I usually get a bemused look first and then a glass of tap water served up with good humour.
Now, if we are going to compare the merits of American beers to those available in Europe, I am happy to believe the comments of our American guests...