- →Ion exchange resin beads swap Ca²⁺ and Mg²⁺ for Na⁺. Hardness minerals are captured on the resin; sodium is released into the water.
- →Salt is needed for regeneration — a brine flush restores the resin's sodium ions so it can soften water again. Ongoing cost: $200–$400/year.
- ✗A softener is not a filter. It removes hardness only. Chlorine, chloramine, lead, PFAS, fluoride — none addressed. A carbon filter is still required.
- ✓Best choice for hardness above 200 mg/L (Perth outer north) or when you specifically want the silky feel of truly soft water.
- !Softened water has sodium added proportional to hardness removed. People on sodium-restricted diets (CKD, hypertension) should keep the drinking tap unsoftened or add RO.
The exchange — calcium for sodium
A water softener contains a tank of resin beads — small polymer spheres with a negative charge that attract positive ions. The beads are initially loaded with sodium ions (Na⁺). When hard water flows through, calcium (Ca²⁺) and magnesium (Mg²⁺) — which carry a stronger positive charge — displace the sodium off the beads. Calcium and magnesium are captured; sodium is released into the water.
The result is genuinely soft water: calcium and magnesium removed, water has the characteristic silky feel, soap lathers more easily, and scale cannot form on any surface downstream.
Regeneration — why softeners need salt
After processing a certain volume of hard water, the resin beads become fully loaded with calcium and magnesium. At this point, the softener runs a regeneration cycle — it flushes the resin tank with a concentrated salt (sodium chloride) brine solution. The high sodium concentration displaces the calcium and magnesium off the beads, restoring them to their sodium-loaded state. The calcium-rich brine is flushed to drain.
This is why salt-based softeners require ongoing salt purchase ($200–$400/year), produce waste water during backwashing, and need a drain connection installed nearby.
What a softener does and doesn't do
A water softener removes hardness only. It is not a water filter.
- ✅ Removes calcium and magnesium — hardness minerals
- ✅ Eliminates limescale in pipes, hot water systems, dishwashers, washing machines
- ✅ Produces noticeably silkier water with better soap lather
- ❌ Does not remove chlorine or chloramine — a carbon filter is still required
- ❌ Does not remove lead, PFAS, fluoride, nitrates, bacteria or sediment
Softened water contains added sodium proportional to the hardness removed. At Perth outer zone hardness of 300 mg/L, softened water contains approximately 200 mg/L sodium. People on medically restricted sodium diets (CKD, hypertension) should keep the drinking tap unsoftened or add an RO stage.
When to choose a softener over TAC
TAC prevents scale without removing minerals and is lower cost and maintenance. A salt softener is the better choice when:
- Hardness exceeds 200 mg/L — Perth outer northern zones (Yanchep, Butler, Alkimos). TAC becomes less effective at very high hardness levels. A softener provides complete protection.
- You want the feel of soft water — the silky sensation and better soap lather only come from actually removing calcium and magnesium. TAC cannot produce this.
- Existing significant scale damage — a softener removes the source material more completely than TAC when pipes and appliances are already heavily scaled.
The right choice for Perth outer northern zones above 200 mg/L, and for households who specifically want the soft water feel. For most Brisbane, Adelaide and Perth inner zone households at 80–150 mg/L, TAC is more practical — lower cost, no salt, no sodium addition.
Remember: a softener is not a filter. You still need carbon filtration for taste and chloramine. See our TAC vs salt softener 10-year cost comparison for the full financial picture.