A softener's running cost is salt, water and a small amount of electricity, and the first two follow from how it is set.
What determines salt use
The grains removed, which is the household's water use multiplied by the hardness. That is fixed by circumstances.
The salt efficiency setting, which is not.
Manufacturers publish capacity at several salt doses. A high dose gives more capacity per regeneration at poor efficiency; a lower dose gives less capacity and considerably more grains removed per pound of salt.
The difference between running a unit at its maximum dose and at an efficient one is substantial over a year, and it is a setting in the valve.
Demand versus timer
A meter-controlled unit regenerates when the resin is actually exhausted. A week away costs nothing; a week of guests is handled.
A timer unit regenerates on schedule regardless, which wastes salt and water on every unnecessary cycle and delivers hard water when demand is higher than the schedule assumed.
Replacing an old timer valve with a metered one pays back on salt alone in most households, and it is a valve rather than a whole softener.
Water use
Each regeneration uses water for backwash, brine draw and rinse — commonly tens of gallons.
At a sensible regeneration interval of three to seven days that is a modest annual figure. At daily regeneration from an undersized or badly set unit it is not.
On a well, that water is pumped and discarded. On a septic system, it is added hydraulic load, and where the field is marginal it is one of the first things to reconsider.
The consequence of sizing
Undersized: regenerates too often, wasting salt and water and wearing the valve.
Oversized: regenerates rarely, using a large dose each time and leaving the bed standing loaded.
Both cost more to run than a correctly sized unit, which is why the grain-load calculation matters beyond just working.
Salt choice and cost
Pellets are the usual choice — low in insolubles, so less sludge in the brine tank.
Rock salt is cheapest per bag and highest in insoluble matter, which accumulates and eventually blocks the brine line. The saving is generally not worth the maintenance.
Potassium chloride costs several times more and is less efficient per pound, so a valve setting adjustment is needed. It is chosen for sodium restriction rather than economy.
The settings worth checking
Hardness, matching a current test plus the iron adjustment. A unit set from a guess will regenerate on the wrong schedule.
Salt dose, at an efficient rather than a maximum setting.
Regeneration time, in the early hours.
Reserve capacity, so the unit regenerates before it runs out rather than after.
Any of these set once at installation and never revisited is worth an evening with the manual.
Electricity
Negligible — a valve motor running for a few minutes per cycle and a small controller.
A salt-free conditioner uses none at all, which is one of its genuine advantages alongside using no salt and producing no discharge.
The other cost
Resin, every ten to fifteen years, faster on chlorinated water or where iron is present.
That is a scheduled expense rather than a running cost, and it is far cheaper than a new softener — which is what is often quoted instead when a bed is exhausted.
Measuring your own
The valve's display shows water treated since the last regeneration on most metered units, and the number of regenerations over a period.
Multiply regenerations per year by the salt dose per regeneration, and that is the annual salt consumption in pounds — a real figure rather than an estimate, and the basis for judging whether a setting change is worth making.