Well, anything you add to distilled water will make it less thermally conductive. For corrosion, just make sure that the metals you are using are about the same on the galvanic corrosion index: http://en.wikipedia.org/wiki/Galvanic_corrosion. All coolants are essentially distilled water + glycerol. Alphacool ultra pure distilled water is overpriced. All you need is distilled water from any source. Walmart sells them in 1 gallon tanks for <10 USD. There is no such thing as "non-electrically conductive coolant", as over time, bits of metal from your blocks will mix in and make the coolant conductive.