Chances are higher that they have their ice delivered - ice machines aren't very common in restaurants. That ice is all nice and pure and stuff. Any ice machines that are being used will have good filtration, lest the ice taste bad and look cloudy. . .
My American love affair with ice is showing. All but the smallest restaurants in the US couldn't survive without an ice machine, and a bar--no way could a bar manage on bagged ice. In the US a restaurant generally figures a pound of ice per customer--potentially hundreds of pounds per day.