Do I need a water softener or a filter?
They're often sold together, but they solve completely different problems. Buying the wrong one is the most common — and most expensive — water-treatment mistake.
A softener fixes hardness. That's an appliance problem, not a health one.
Hard water is high in calcium and magnesium. It doesn't harm your health — it scales up water heaters, dishwashers, and pipes, leaves spots, and stops soap from lathering. A salt-based softener is the only thing that truly removes hardness (via ion exchange). A salt-free conditioner is a different technology: it helps prevent scale from forming but does not remove hardness, and its effectiveness drops in very hard water (above ~25 grains per gallon). If you see white scale and your soap won't lather, you have a hardness problem.
A filter removes contaminants — for taste, smell, or health.
If your concern is chlorine taste, sediment, iron staining, a sulfur smell, or a health contaminant, that's a filter job, not a softener job. Which filter — and crucially where it goes — depends on the contaminant. Chlorine, iron, and sulfur are whole-house concerns; PFAS, lead, nitrate, and arsenic are best handled at the drinking tap. See the exposure-route guide →
When you need both
Plenty of homes — especially on wells — have hard water and a contaminant. A common correct setup is a sediment pre-filter, a softener for the hardness, a carbon stage for chlorine or odor, and (where the water is unsafe) UV — then a small under-sink reverse-osmosis unit for anything you drink. The selector builds the right stack for your specific answers and sizes it to your home.