I don't understand a lot of this from the theoretical point of view, but the lesson I get from this is:

If 0.01 g/sqm residue is "commercially" sufficient, than Greg tests give peace of mind to all those who follow this procedure, provided the water is not significantly different;

To take into account difference in water quality, add another rinse. No problem.

Because 0.01 g/sqm might not be enough for archival quality, add yet another rinse and you'll have archival quality anyway, so that your grand-grand-nephew can make observations about your pictures, after having already inherited from your heirs that is.

So any published method for washing is good for most purposes (thanks Greg) and if you really want to be sure to reach archival quality just add a rinse or a couple of rinses (thanks Erik) for your descendants' enjoyment.

Fabrizio
Water is cheap.