My worst horror story was a full server room shutdown. We killed servers, then the chillers, and then started work. About an hour after we started, we pulled our first floor tile to move some power cables. There was water under the floor! We spent the next few hours cleaning up all the water.
Apparently water kept flowing into the humidifier tray of the chiller, and the mechanical auto-shutoff never triggered. The pump didn't remove water from the tray because the power was off.
Facilities "fixed" the humidifier, but it still happened again when that circuit was cut off for work elsewhere in the building. No one caught the water overflow, and it flowed out down the conduits to the first floor. So we had flooding on 2 different floors from a single chiller.