New tests showed no sign of E. coli bacteria in the water supply of an upscale Seattle suburb, officials said Friday, but residents should still boil water and restaurants should stay closed unless they meet rules for serving prepared foods that don't require water use. E. coli first was found in Mercer Island’s water on Saturday: All restaurants and schools there were ordered closed, grocery stores threw out water-washed food, and the city’s 23,000 residents were told to boil their drinking water. On Thursday, another sample tested positive, and the city renewed the boil warning and restaurant closure order, said Ross Freeman, the city’s communications manager. Schools reopened Tuesday and planned to stay open Friday, using bottled water and meals that don’t require water to prepare, the school district said.
Where the E. coli came from isn’t known. The city said crews injected extra chlorine into the system to eliminate the contamination and ramped up testing to try to find the source. Tests released Friday found no E. coli, the city said, but health officials still want to see at least another day of clean tests before the orders were lifted. The island in Lake Washington, reached by Interstate 90, gets its water from Seattle Public Utilities, which has said the contamination appears confined to the island.