I was looking into this at one point, One of the things I want to do is build an immersion cooled computer, I probably never will because the whole thing sounds

I was looking into this at one point, One of the things I want to do is build an immersion cooled computer, I probably never will because the whole thing sounds like a big mess. But I do like researching the idea every now and then. So on the question of what coolant to use. water, by far, has the best thermal properties. But water also tends to have annoying electrical conduction properties. However, pure water is not conductive. So I start looking into what it would take to add a water deionizer to the coolent loop. At which point I find out the when water has no ions it wants them and will happily start striping them from metals. including all those lovely copper ions in your pcb traces. With a heavy heart I had to discard deionized water from my list of possible coolants.