The "don't use distilled water statement" applies to running STRAIGHT distilled water. Guys actually used to do this way back when, but without corrosion inhibiuitors a few metal ions will dissolve from the metal surfaces in contact with the water and you have a battery! If the engine has dissimilar materials such as aluminum and cast iron, the aluminum will rapidly corrode.

When using ANTIFREEZE, it is best to use distilled water, so you don't introduce any additional salts in the system. Chlorine in particular is not good, however, most manufacturers say that "potable drinking water" is okay to mix with antifreeze.

Duke