The clearest way to separate these two is to describe what comes out of each one, because the marketing language obscures a straightforward chemical difference. In one case the water leaving is genuinely different from the water arriving. In the other it is chemically identical and behaves differently on surfaces, which is a real effect and not the same thing.
What leaves a salt based softener
Water with the calcium and magnesium removed and a small amount of sodium in their place, in proportion to the hardness that was taken out. That is ion exchange: the resin holds sodium, swaps it for hardness minerals as water passes, and is recharged with brine when loaded. A hardness test on the treated water reads soft. Soap lathers because there are no minerals to react with it. Nothing is deposited on heating surfaces because there is nothing left to deposit.
What leaves a salt free conditioner
Water with exactly the same calcium and magnesium content it arrived with, but with some of it converted into stable microscopic crystals suspended in the flow rather than dissolved. A hardness test reads unchanged, because the minerals are still there. Soap behaves as it did, because it still has minerals to react with. What changes is deposition: crystals already formed in the water are far less inclined to stick to pipe walls and heating elements than dissolved minerals coming out of solution on a hot surface.
Why the sodium question is usually small
The amount of sodium added is proportional to the hardness removed, so it is larger on very hard water and modest in the hard band. For most households it is not a dietary concern, and where it matters, the standard answers are to leave the kitchen cold tap on the unsoftened line or to fit reverse osmosis there, both of which are cheaper than not softening. Potassium chloride can be used as the regenerant instead, which puts potassium in the water rather than sodium.
Choosing on the outcome you want
If the goal is soap, laundry, glassware and the removal of existing scale, only the salt based route delivers it, because those depend on the minerals being absent. If the goal is protecting a water heater and pipework with no salt, no drain and no power, conditioning delivers that. The USGS puts hard water at 121 to 180 mg/L as calcium carbonate and very hard above 180, and in the upper band removal is the more dependable choice. Our salt free softener guide covers the units.
Questions people ask about salt based vs salt free water softener
What is chemically different about softened water?
Calcium and magnesium have been removed and replaced with a proportional amount of sodium, so a hardness test reads soft.
What does a salt free conditioner change?
Not the water's mineral content. It converts some hardness into stable crystals that are far less inclined to stick to surfaces.
Is the added sodium a health concern?
For most households, no. Where it matters, leave the kitchen cold tap unsoftened or fit reverse osmosis there.
Which should I choose?
Removal for soap, laundry and clearing existing scale. Conditioning for equipment protection with no salt, drain or power.