Guys, do not ever feel pressured to buy something else than water if you don't want to. Restaurant owners ought to realize that they cannot simply control what their diners are ordering. In fact, GOOD managers and restaurant owners will factor that in their budgets. People only ordering water are hardly a new thing or rare...
If you get some attitude from the waiter / waitress, I suggest you complain to the manager, or simply do not tip.
Customers really have to stand for themselves. The whole god damn service industry out there make a shitload of money off people being either meek, lazy, ignorant, stupid, or a combination of these...