Daily Mail: We’ve all been there, thinking about whether to ask for tap water in a restaurant: “Will the waiter refuse me? Will he accept, but grudgingly, with a raised, slightly superior, ego-bruising eyebrow?” Worse perhaps: “Will the person I’m with think I’m being tightfisted, willing to sacrifice quality just to save some money?” We Brits pride ourselves on our common sense. Yet, paradoxically, even though our drinking water is some of the best in the world, and …