John Morgan's story reminded me of my own, similar experience.  A colleague
and I wandered back to the office one evening during a very heavy downpour.
 On opening the computer room door, it was like walking into a big shower.
Water was dripping from dozens of points in the (tiled) ceiling!

The installation - a 922, 7978, 2 * 2563 and 2 DTCs, was taking the brunt
of this.  The thick carpet (the computer room was _not_ ideal) was under
water.  Needless to say, the 3000 was still running.

It transpired that the flat computer room roof was surrounded by higher,
ridged roofs, and a blocked drainage point had allowed the water level to
rise, trapped by the other roofs, until it found a weak point and entered.
Then, the U-section rails which supported the ceiling tiles acted like
mini-aquaducts, distributing the water around the computer room.

After a hasty shutdown, we poured the rainwater out of the DTCs(!), got the
carpet pumped dry, opened up everything that was openable and put all the
available fans on to dry out the hardware.  24 hours later we started up
the system again.

All this happened 5 years ago, and the same equipment is still running with
total reliability.