The Dalles Public Works Department has repaired a 12-inch water main, continues to repair multiple broken water pipes in an area of the city east of Lewis Street to Thompson Street from East 9th to East 19th, and issued a boil water advisory that is expected to be in effect for the next couple of days.  Public Works Director Dave Anderson says a pressure regulating valve near Mid-Columbia Medical Center failed late Wednesday night, allowing highly pressurized water to go into surface zones below that valve, leading to broken pipes and pressure relief valves on water heaters to open and drain water into some houses.  Anderson says they are in the process of refilling and repressurizing lines in the impacted area.  Anderson says because of the loss of water pressure in the system after the incident, there is the potential for harmful bacteria to be present.  Customers should bring water to a rolling boil for one minute, then allow it to cool before using it for drinking, washing fruits and vegetables, making ice, brushing teeth, preparing food and baby formula, and cleaning food surfaces.  The water is safe for handwashing, and City officials say the boil water advisory has been issued as a precaution.  The department says if you are outside of that general area but also lost water service Wednesday night or Thursday morning, you should follow the advisory.  A map showing the affected area is available at thedalles.org.  Anderson said they don’t yet know exactly why the regulator valve failed.  About 600 properties were impacted by the incident.