What a Water Softener Actually Fixes, and How to Size One
A softener filters nothing — it exchanges ions. How regeneration works, what grain capacity measures, how to size one to your hardness, and what it does not do.
Category Guide
Water Softeners: Hardness, Ion Exchange and Sizing
Hardness, ion exchange and what a softener does and does not fix.
Guides
How to choose
Quick answer
A softener is not a filter. It exchanges the calcium and magnesium that cause hardness for sodium or potassium, which stops scale forming in pipes, heaters and appliances. It removes no contaminants, disinfects nothing, and does not improve taste on its own. Sizing comes from two numbers multiplied: hardness in grains per gallon from an actual water test, and daily household usage.
What to compare
- Grain capacity, not tank dimensions. Two units of similar size can carry very different ratings depending on resin volume.
- Service flow rate in GPM. Capacity decides how long it lasts between regenerations; flow rate decides whether it keeps up when several fixtures run at once.
- Metered versus timed regeneration. Demand-initiated units regenerate on measured usage and generally use less salt and water than fixed-schedule ones.
- Sodium chloride versus potassium chloride, and whether you want an unsoftened or RO line at the kitchen tap.