Cavitation pitting is a big problem in wet-sleeve engines like the DD engines, not sure it is really an issue in a dry-sleeve engine like M-B car engines, ... correct me if I'm wrong.

I use distilled. What you want in water is something that doesn't conduct (pure water doesn't conduct electricity), that reduces dielectric corrosion problems where you have metals with different electrical potentials (eg: aluminum and iron) sharing the same water, proper pH should be handled by the additive package in the "anti-freeze", and proper wetting should be accomplished by the anti-freeze also. A fluid devoid of minerals or dissolved solids helps to prevent the buildup of sedimentary deposits as does proper pH, distilled water shouldn't have any dissolved minerals/solids.

- Jeff Miller
190DT