The water boil advisory for central Louisville is expected to remain in effect until this evening.The advisory was put in place last night after a 48-inch water main broke on the University of Louisville campus. It covers the area north of the Watterson and between Ninth Street and Bardstown Road and Baxter Avenue.The advisory is a precaution that's put in place whenever water pressure drops significantly. There have been no confirmed contaminations, and the company won't know if there are until tonight."I think we won't be able to lift it until after 8:00 tonight," says Louisville Water Company spokeswoman Kelley Dearing-Smith. "Whenever we have a main break, we take a series of water quality samples and it takes time to get those samples to a point when we can read them."The water company is also investigating the cause of the break today."From what I understand from our records, the last time this pipe was inspected it was fine," says Dearing-Smith of the roughly 80-year-old pipe. "So who knows what it was. At this point it could be the weather, it could be a freak accident, it could be stress on the pipe we didn't know about. It could be construction activity from years ago that could've caused something like this."The University of Louisville's Belknap campus was flooded when the main broke and is closed today. Humana's downtown offices are also closed.