PORTLAND — Merrick Monroe popped the tab on a Pabst Blue Ribbon, giggled and took a swig.If Portland’s boil order was going to forbid drinking tap water during Friday’s work hours, Monroe pledged to find an alternative. She discovered it in the back room of Bridge City Comics, where she passed an otherwise quiet Friday afternoon as cashier.“After I got into work, I was texting with my boss and we were joking about stuff, like, what are we gonna drink?” Monroe said. “He said there’s plenty of PBR and bottles of water in the back, so, I guess I’m drinking PBR.”On Saturday, the city lifted a 24-hour boil order, the largest in the city’s history. The news was welcomed by coffee shops, restaurants and bars that had to close or serve limited menus on Friday evening and Saturday morning.Tests discovered the presence of the E. coli bacterium in the city water supply over three days beginning Tuesday.Water customers were told to boil all drinking water for a full minute, avoid getting water in their mouths during showers and throw out anything made with tap water during the previous week.Two city reservoirs will be drained and cleaned. The city hasn’t yet identified the source of the contamination, and the water bureau advised customers to run all taps for two minutes to purge potentially contaminated water.