Dallas County, Texas lost its IT systems for three days when a broken water main flooded the basement of the building where all the county's servers are housed. The servers were fine--they are located on the fifth floor. But the UPS and other electrical equipment supplying power to those fifty floor servers were located in the basement, where water flooded in from the broken main.
This was a huge problem in New Orleans during Hurricane Katrina. Many data centers were on upper floors of the flood-prone area, so the data equipment was fine. But what knocked out a lot of telecom centers was the fact that the back-up generators were all on the ground, or in other words, under water. When the power went off, the generators were not able to keep things running because they were flooded. Some may remember that one small ISP with its generators on an upper floor kept its Internet connection up during the entire flood. The intrepid group had spouses and wives bringing food in, and other friends and helpers were bringing diesel fuel to their building in fifty-five gallon drums.