Doc, thanks very much for continuing to maintain this thread. I'm new to this stuff, I think that a lot of the trouble I'm having getting started is water-related, and I'm looking for practical solutions. I get what you're saying about grocery-store RO, but that doesn't really work for me, as the cost is significantly higher here and the distance to haul it long. So I need to figure out the right way to process my water on-site without breaking the bank with capital costs. I read this thread hoping to find a little more detail on how to attack the problem, but so far you've been a little light in that regard.
I'm working with well water, very hard e.g. 750ppm. I haven't had it analyzed, though I think that's going to happen soon. The calcium content is obvious from shower-head cloggage and the carbonate residue left on pots, and I think the iron is high as well, judging from the rust ring at the water line in the toilet. I have both a conventional salt (NaCl) softener and a consumer-grade RO. The question is whether these pieces in the right combination can solve the problem.
Reading the RO unit's specifications, they set ceilings on Mn (<.05ppm), Fe (<.1ppm) and TDS (<10gpg). That suggests that feeding hard water directly into the RO is going to fuck it up, probably by clogging the membrane. Preconditioning the water with the softener is going to yank out that stuff and add the undesirable Na, but since their specifications don't say anything about sodium that should be okay, and suggests that it'll in turn be removed by the RO. In fact, in the footnotes in the RO specs they say their ratings are based on a "supply TDS 250ppm softened tap water".
So does hooking it up in that order make sense to you, both in terms of the desired water chemistry and component longevity?