THE DILEMMa  Is tap water really safe to drink? I know it's the eco thing to do, but I worry about drinking recycled sewage.  I was surprised last week when a friend recently relocated from Italy expressed doubts about good old London tap water. But then she was even more surprised by my jauntily ordering it with a meal. "Is it really safe?" she whispered. apparently I could neither quench nor quell her fears. after a heated exchange she bottled it, opting for the packaged H2O option she finds comforting.  But I concede that "recycled