The power of water

On Sun, Oct 20, 2002 at 12:22:50 -0400, Howard C. Berkowitz wrote,

3. Consider putting data centers not in the ground floor on the basement,
    but not too high either. Sean, I believe, knows the specific NFPA rule,
    but IIRC you can't have a UPS with acid electrolyte above the third floor.
    So, you can put a data center on the 2nd floor and both allow the UPS
    and have a place for the water to drain.

This is not at all my area of expertise, but I'm curious, why does
does the UPS need to be on the same floor with the data center racks
at all?