Watch out for the term "acid" and "acid-free" in paper products. Those terms are not specifically referring to the pH but rather the selection of the paper making method and the sizing material used in the paper. The reference to acid and acid-free is commonly used because old non-archival paper stock used acid sizing agents that gave rise to degradation of the paper. However, this is not the end of the story. Many (if not most or all) pre-WWII photographic paper products were made on an acid paper but many of the high quality ones are still going strong in proper storage.
Addition of alkaline agent in wash water or final rinse bath is not going to convert an acid paper to non-acid paper, as the term is, again, not specifically referring to the pH. Adding an alkaline agent to acid-free paper (most if not all current photographic paper stock) doesn't make much difference, if the alkaline agent is harmless. I'd suggest to avoid this unnecessary step unless there is a specific (and good) reason to do so. Incidentally, most tap water is on the alkaline side, and in case of Boston area municipal tap water, the pH is about 9.2.
John is referring to a summary of a series of studies made by Levenson, Green, and others at Kodak Harrow Lab. It is not really the "mineral" component but some ions present in tap water that accelerate the washing process. Some ions (such as acetate/acetic acid) retard washing as well. Distilled or otherwise purified water is a poor choice for washing. Otherwise, a combination of sulfite-based washing aid and tap water is the most effective and most well tested method. I've done rather exhaustive survey of washing techniques, old or new, and considered the efficacy, cost, lack of potential harm to the image, ease of use, etc. There is no killer magic in this area. Sulfite is preferred over bicarbonate as the washing aid, since sulfite is more effective in removing some argentothiosulfate complex ions, whose concentration increases sharply in partially used fixer bath. Removal of this complex is important for archival prints.
Water can be conserved to a rather small quantity by using counter-flow cascade and fill-and-dump technique together. I don't think I had this recommendation when John asked me last time. I've tested fill-and-dump technique with various fiber papers in a tray, using Silvergrain Clearfix, Clearwash, and cold (about 4-5C) winter tap water. Practical recommendation (which incorporates a safety factor and exceeds current archival standard for residual thiosulfate level) is described in the technical info sheets of these products, which can be found at Digitaltruth site. For those who like to mix from scratch, you can do the same with my published neutral rapid fixer formula and 20g/L of sodium sulfite as the washing aid working solution.
