The two commodities we need most in a disaster in order to continue operating is electricity and water. Water is a basic need that sustains life and in other applications cooling for computers or people. In hospitals it is a basic need to eliminate the possibility of infection and just plain old sanitation.
Sandy has pointed out how when a disaster hits an urban area what happens when the water and electricity stop flowing. Several hospitals closed. One for power and the other for a lack of water. I'm also just guessing the availability of staff was also an issue since the "normal" commute was out the window. My nephew who works in Manhattan and lives in the Brooklyn took a taxi to get to work in the morning, a journey that took three hours. To get home he waited for a bus and then ended up walking home, which took four hours.
What I have found is that architects and engineers like to put things like generators that support a building's critical systems in the basement. It is were many of the other systems are located and when running the noise and vibration are not as big an issue. Of course, when there is a flood...the best plans often don't pan out the way you thought they would.
When we designed the King County Regional Communications and Emergency Coordination Center (RCECC) we paid a great deal of attention to the generators. We had two, one redundant to the other. There was also a 6,000 gallon tank of water on site. Where we missed the mark was on the amount of fuel storage for the generators. We could not justify to the "money minders" that we needed more than three days of fuel. They thought that the facility as critical as it is could be refueled if need be. That of course could be problematic in a catastrophe.
Think about where your generator is located and how much fuel you have available. Do you have a supply of potable water?