I've seen a number of suggestions in this and the 240 BB regarding flushing and refilling cooling systems and many of these suggest using distilled water along with the coolant. A while ago on the MGB board, (yes, I balance the pragmatic good sense of owning a Volvo, with the lunacy of a British sports car...) a Chemical Engineer cautioned against this and recommended softened water instead. He worked in the process industry, and had seen major corrosion problems resulting from distilled water use in situations where it can come in contact with CO2 and/or other gasses. The reason is, it has no "buffering" capability, and will quickly turn acidic when those gasses dissolve in it. IE: it becomes an electrolyte with serious corrosive capability.

Softened water contains compounds which will absorb/neutralize (buffer) most of such acidic reactions, and continue to be relatively harmless to metals. Perhaps the blending of "antifreeze" with the water makes the whole point moot?

Anyone out there with a chemistry background who can comment? Personally, I've used soft water for many years in my cars' cooling systems and seen no noticeable corrosion. The '83 244 is still on its original radiator and heater core and both function as new.
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Bob (81-244GL B21F, 83-244DL B23F, 94-940Sedan B230F)