Cation-exchange resin regenerated with sodium or potassium chloride. Removes hardness. Sends brine to a drain unless it is a portable-exchange tank regenerated off site.
Salt-based softener: two mineral tanks and a brine tank.
What it actually does
Exchanges calcium and magnesium ions for sodium or potassium, which is what NSF/ANSI 44 and EPA WaterSense mean by residential softening.
What it does not do
Does not remove chlorine or chloramine, does not strip hydrogen sulfide, and only handles limited ferrous iron — it is not an iron/sulfur filter and not a PFAS device.
Brine / salt discharge
No on-site brine if it is a portable-exchange tank; self-regenerating units discharge
Typical use
Hard or very hard city or well water where soap performance and scale removal (not just scale behavior) are the goal, and where the sanitation district allows on-site brine or a portable-exchange exception applies.
Certification language
NSF/ANSI 44 is the residential cation-exchange standard (material safety, integrity, capacity, brine accuracy). A voluntary efficiency rating under 44 uses stated salt and water-use thresholds. Search the certifier directory for the assembled system or named components.
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This is the appliance people mean by “softener.” Resin beads take Ca²⁺ and Mg²⁺ and give Na⁺ or K⁺. When the bed is full, salt brine regenerates it and a chloride-rich waste leaves the house.
That waste is why LACSD / Santa Clarita prohibits automatic units on the sewer. Portable-exchange tanks still soften; the brine is made at a plant.
