By Lori Kersey VIENNA - Standing in her Vienna restaurant during the lunch-time rush Friday, Cindi Emrick had mostly questions and frustration about an advisory not to drink or cook with the city's tap water. Nothing about the water had changed overnight in the city near where DuPont Co. had for years been making the chemical C8, so why was the Environmental Protection Agency changing the allowable limits so drastically now, she wondered. "Why are we panicking?