Distilled water is surprisingly corrosive. Water is actually a very good solvent, but most water you encounter is already so saturated with dissolved minerals and such that it seems mostly inert.
Distilled water would work for a while, but will literally dissolve the metals on your board. Conductivity will of course creep up over time, but your main concern should be that the widget you're trying to cool is getting eaten by the coolant.
As an example, you may have noticed that air conditioner condensate can damage concrete. The condensate is pretty pure water, and physics really wants it to be less pure. The water is so reactive that it can rip the minerals out of cement, leaving just the aggregate behind.
If all that weren't bad enough, once you put a PCB in pure water and it starts leeching ions, you suddenly have an electrolysis bath with dissimilar metals. If you can't maintain the purity of the solution, you'll have a very bad time.
>In order for the light from these shockwaves to reach the sensors, the water has to be cleaner than you can possibly imagine. Super-K is constantly filtering and re-purifying it, and even blasts it with UV light to kill off any bacteria.
>Which actually makes it pretty creepy.
>“Water that’s ultra-pure is waiting to dissolve stuff into it,” said Uchida. “Pure water is very, very nasty stuff. It has the features of an acid and an alkaline.”
>“If you went for a soak in this ultra-pure Super-K water you would get quite a bit of exfoliation,” said Wascko. “Whether you want it or not.”
>When Super-K needs maintenance, researchers need to go out on rubber dinghies (see above) to fix and replace the sensors.
>Matthew Malek, of the University of Sheffield, and two others were doing maintenance from a dinghy back when he was a PhD student.
>At the end of the day’s work, the gondola that normally takes the physicists in and out of the tank was broken, so he and two others had to sit tight for a while. They kicked back in their boats, shooting the breeze.
>“What I didn’t realise, as we were laying back in these boats and talking is that a little bit of my hair, probably no more than three centimeters, was dipped in the water,” Malek told Business Insider.
>As they were draining the water out of Super-K at the time, Malek didn’t worry about contaminating it. But when he awoke at 3 am the next morning, he had an awful realisation.
>“I got up at 3 o’clock in the morning with the itchiest scalp I have ever had in my entire life,” he said. “Itchier than having chickenpox as a child. It was so itchy I just couldn’t sleep.”
>He realised that the water had leeched his hair’s nutrients out through the tips, and that this nutrient deficiency had worked its way up to his scalp. He quickly jumped in the shower and spent half an hour vigorously conditioning his hair.
>Another tale comes from Wascko, who heard that in 2000 when the tank had been fully drained, researchers found the outline of a wrench at the bottom of it.
>“Apparently somebody had left a wrench there when they filled it in 1995,” he said. “When they drained it in 2000 the wrench had dissolved.”
Part of that story sounds suspect. Hair is dead, besides the root/follicle. How could you remove nutrients from your scalp by doing anything to the end of your hair?
I wonder if the reporter didn't catch on and he actually had his head hanging in the water (so the water was touching his scalp).
Also the "even blasts it with UV light" isn't actually that weird. We have a well and we treat the well water with a UV light disinfector. What's stranger is why you'd need to worry about bacteria growing in ultra-pure water. What would the bacteria eat?
Distilled water would work for a while, but will literally dissolve the metals on your board. Conductivity will of course creep up over time, but your main concern should be that the widget you're trying to cool is getting eaten by the coolant.
As an example, you may have noticed that air conditioner condensate can damage concrete. The condensate is pretty pure water, and physics really wants it to be less pure. The water is so reactive that it can rip the minerals out of cement, leaving just the aggregate behind.
If all that weren't bad enough, once you put a PCB in pure water and it starts leeching ions, you suddenly have an electrolysis bath with dissimilar metals. If you can't maintain the purity of the solution, you'll have a very bad time.