Dan,
I don't know where you are in the Willamette Valley, but I spent years in Eugene and had no real hard water problems.... And, this is just some brainstorming, not really an answer to your question, but...
Anyway, here in Vienna, my water is failrly hard (mixing solution B of PMK in tap water is impossible, even with twice the volume). I do use distilled water for mixing developer stock and wetting agent, however, I use tap water for all working solutions, (I adjust developer times according to tests). Stop and fix are no problem at all. The little printing I do here is all with tap water. What I'm saying here is that, except for a change in developer activity, which I compensate for, I find no problems with using hard water for processing except for mixing developer stock solutions and for the final rinse for negatives. For this I just buy 5-liter jugs of distilled water.
In the States, I often just get the 25-cent-per-gallon drinking water from the vending machines found in hard-water areas when I need something other than tap water. It works even for mixing stock and final rinses since the mineral levels are very low.
I'm curious as to why you feel you need large volumes of distilled water. If you are on a well with lots of possible contaminants, then cheaper drinking water or demineralized water should work for most of your needs. If you do need large quantities, maybe you should look into an RO system...
Best,
Doremus Scudder
www.DoremusScudder.com