Ok, they way I would suggest doing it is to use a separate PSU for the water cooling gear and use a relay powered by a molex plug from each one of the systems. However you would need to do a resistor in line on each of the 12v lines coming from the computers to prevent 12v power flowing back to the powered off system. You will need to look that part up, but I am pretty sure it would work. Essentially what you are doing is using a molex connector from the system PSU to energize a relay that will then connect the ground wire and green wire on the water cooling PSU telling it to turn on, sort of like when you want to use a PSU to do a leak test without turning the MB on. The main concern here is preventing feedback from one system to the other which the resistors should do, I am just not sure of which ones to use.


Then you could use one pump, one res and one rad to cool the water blocks on each side, wouldn't matter if the computer was on or off, the water would still flow through the blocks. You could use the new Primochill Typhoon 3 instead of use "Y" adapters which would hurt your flow.

The other option of course is to just use a separate water cooling setup for the business machine. Depending on the gear you could use something simple like the Swiftech H2O-120 which is just two parts, even the H2O-220 is the same but with a dual rad. Very good systems and very simple and compact.