If it's a place that serves tea and coffee, there's a pretty good chance they'll do decaf or green tea.
I don't recommend drinking three pints of it, though.
If you're a regular, you might be able to persuade them to try a few other 0% beer options, like Guinness 0% or "Nowt Peculiar" etc
Otherwise, yeah, it's water or fizzy water, optionally with some juice or cordial in it.