Hmmmm. This thread has more diverse opinions regarding coolants than I expected.
Usually when similar topics surface, someone is usually quick to quote "chapter and verse" from Da Book, or other credible DD source. This generally trumps and comments that begin "My Uncle Barney always told me to use..."
So, I'll reference the following document direct from Detroit Diesel:http://www.detroitdiesel.com/Public/brochures/7SE298.pdf
It specifically recommends that distilled or deionized water be used. If another water source is going to be used, it lists an entire chart with tests for hardness and presence of other minerals to help determine if the source is suitable.
It also specifically states that automotive type antifreeze products are not to be used, based on the fact that they generally contain high phosphate and silicate levels.
Lots more info in the 31 pages for your reading enjoyment.
Personally, my 6-71 gets a cocktail of DD Power Cool and distilled water. Shaken, not stirred.