It turned out that part of an external wall of the data centre wasn't completely waterproofed. Guess which part of the wall the burst pipe was closest to? Water actually came into the main data centre room under the false floor, and not just a little bit of water. There was enough water that it was coming in through the wall, through the main server room, and out the front entrance of the building in a visible stream. All the power and data cables under the false floor were on raised trays in case of a "water under the floor" problem, so the situation wasn't as dramatic as it looked, and all the systems stayed up, but it had some managers running in circles for the day. The waterproofing of the external walls was upgraded soon after that.