I was thinking it would be smarter to water cool with distilled water because there arent any ions to conduct electricity but I was thinking maybe the heat capacity would go lower?? not a chemist do know a little about chemistry. Any help is appreciated.

Deionized water is what you mean? Distilled is not good enough. Nonetheless even deionized will loss it's properties and then conducts electricity over time. If you're confident enough that you liquid cooling system will not leak them it's good to use distilled or deionized water with a bit of anti-freeze. I myself used non-electrical conductive cooland in my system.

If you can find deionize & distilled water you might as well use it, but regular distilled water works fine. If I every wc my pc I'm going to use Bidest water, it's completely sterile.

thats the thing im not confident enough to know that I wont have any leaks so I was wondering if some distilled water were too leak if it would damage any of the parts.

If water gets on the components there's always going to be a chance of damage, no changing that, and the likely hood of damage if you use deionized water instead of plain distilled is only slightly less. 'Course, if it's only a couple drops it probably wont hurt anything, and if the pc is off when the leak happens, as long as everything is dry before turning the pc on, everything should be fine. Like I said, if you can find the stuff, use it, but don't go out of your way to get it. The only 100% safe liquid to use in wc'ing is something like ultra pure mineral oil, which is used to cool and insulate high voltage transformers and such.

I just use tap water, has not been a problem for me but dont forget I also add coolent restore 1/3 water 2/3 coolent restore.

Galvanic corrosion is a big problem in mixed-metal cooling systems. If your block and your rad are both aluminium OR copper, no probs. Aluminium/copper mixed will result in galvanic corrosion.

Anti-corrosion agents for cooling systems are available - most car antifreeze have such chemicals. Distilled or even RO water won't allow corrosion at first. It will happen eventually though.

The only way you won't get galvanic corrosion in any mixed-metal liquid cooling system is by using electrochemically inert coolant (the majority of the cooling fluid from Zalman, Cooler Master, etc etc), water-based coolant with a degalvanising agent added (most car coolant additives) or industrial-grade coolant (which I use, and if you want to use it, make certain you're not the sucker paying for it!).

Thing with industrial-grade coolant, is that it's not really that much more effective than most coolants available for the enthusiast PC market. About the only pluses I've found is that it takes slightly longer to get hot than normal coolant, and brag value.