As an alternative to a conventional salt-gobbling, kitchen-cabinet filling, water-wasting softener, I'm planning on installing a whole-house Combimate (made by Cistermiser).   This is one of those polyphosphate micro-dosing thingies (it adds about 2–3 ppm of food-grade polyphosphate, which sequesters the dissolved calcium, so reducing scale). @JSHarris almost certainly knows about the idea, but I thought of him when I read the claim that it's also good for red/brown water from borehole