The distilled water issue has at times become as heated as the green vs. non-green coolant argument and dino oil vs. syn. oil.
A tech named Stu Ritter on the Ritter-Easley MB forums says NOT to use distilled water in MBs.
I asked this same question a few yrs. back. The thread is below.
http://www.peachparts.com/shopforum/showthread.php?t=6923&highlight=distilled