We are not sure whether the owner of the premises will like it, so we prefer not to ask and make a fuss.
Restaurants are well aware of this, and some of the less scrupulous ones exploit it.
It could be said we only have ourselves to blame for not speaking up for what we want, but all restaurants should provide tap water free of charge and they should all be up front about offering it – after all, it costs them nothing.
Although restaurants and bars – and any other venues which serve alcohol – are legally required to offer tap water to customers under terms of the Licensing Act, most cafes, technically, do not have to do so. But they should.
Eating out should be all about the experience. Making customers feel uncomfortable – or indeed that their meal was unnecessarily pricey – might make a few quid on the bill, but is poor business.