Back when mainframes were silicon transistor logic (not CMOS) we used water cooling on the big ones. They had a 3hp Gould pump (actually 2, one was a backup) and they ran hoses under the floor to the CPU frames, pumping distilled water. This was heat exchanged to glycol (customer water) that went to a big chiller (again usually 2 in parallel for backup).
I've always wanted to build a water cooled computer, obviously nothing on the scale mentioned above, but my only real fear in a system like that is a coolant leak.
The logic itself was on chip that was mounted on a stainless plate, another stainless plate with water flowing through it bolted to that with heat sink compound between them.
Stainless??
I would have thought that copper would give better heat transfer properties.
