The Japanese reactors had backup generators for the cooling systems. Then the earthquake and tsunami happened, flooded the ones that were in the basement, and the roads were in no shape to allow for fuel deliveries for the generators, or to truck in replacement generators.
On 9/11, NYC's main emergency command center was on the 23rd floor of 7 World Trade Center.
We will eventually find out what sort of disaster will knock out the generators for the water system.
We do what we can. Our biggest threat is a hurricane so that is how we are designing it. It will be very helpful when the next Ike comes roaring through.
It is better than letting people die from lack of water.