Most data centers I've worked in have backup batteries and generators. This works well when the power is off. I was working at a big bank in a major metropolitan area that had a water main break nearby. No water meant no chillers. No chillers meant no cooling. No cooling meant all the systems got shutdown. In a big bank this meant all the online systems came down like ATMs, wire transfers, check processing and the brick and mortar branches.
After a few hours the big bank officers convinced the city to get a fire truck to lay fire hose from the nearest working hydrant to the chillers. This let us everything back online until the water main was repaired.
We're budgeting water wells for backup incase a main breaks in a few jobs we're working on...
(Also, it's the cooling towers that need all the water, not the chillers, chillers run in a closed loop. Now air cooled chillers you would need no water at all, except they're energy hogs)