the water here (near Nogales, AZ, USA) is pretty seriously hard and as far as I can tell there is no one perfect solution to this.
My present solution is:
1) drinking and cooking water:
hard water provided by the utility->
water softening using either NaCl or KCl->
Reverse Osmosis Unit removes most (not quite all) of NaCl or KCl->
water distillation (remove as much of the remaining salt as I can)->
any waste goes to septic.
2) landscape water:
no processing - this just comes from the utility
3) all other water for washing, etc.:
hard water from utility->
softened with NaCl or KCl->
any waste flows to septic
There are various pros and cons.
Failure to soften the water means that cleaning is more difficult. I have also heard different schools of thought as to whether it is healthy to drink such hard water, and then there are different opinions about whether it is healthy to remove the minerals.
There is more than one area of energy and water use to process the water (water softener is plugged in, and uses up some water, distillation requires a substantial amount of energy, reverse osmosis unit I think uses up water?, energy expenditure of going to store for bags of NaCl or KCl).
KCl around here is very expensive (about USD $24 per 40 or 50 pound bag as versus about USD $4-$6 for NaCl bag) and very difficult to get. However, given all the prominent comments about the dangers of consuming sodium (in particular), it seems advisable to consider issues that may come up if one softens with NaCl. I'm not convinced that consuming much of either Sodium Chloride or Potassium Chloride is great for a person).
If anyone has any thoughts, they are welcome. I guess I'd quickly add that I probably won't immediately (or even in the mid-term) jump on any recommendations. For one thing, some things can be expensive. For another thing, there are a lot of complicated pros and cons to consider about the many suggestions that one might run into, in this area. Often devices recommended as being salt-free may have considerable drawbacks. Long-term, some sort of rainwater harvesting is an option ... but there are only a couple of monsoon seasons per year around here to gather the water, and so one concern is I'm a bit wary of drinking water that may sit for months and months in a cistern of some sort (not to mention all the other aspects of that, such as the expense, permits, etc.).