Why softening trades one mineral problem for a sodium tradeoff — not a free upgrade with no downside.
Hard water is water carrying a relatively high dissolved concentration of calcium and magnesium minerals, usually measured in grains per gallon (gpg) or in milligrams per liter as calcium carbonate equivalent (mg/L as CaCO₃) — roughly 1 gpg ≈ 17.1 mg/L. Those minerals cause genuinely practical problems: they precipitate out as hard mineral scale inside pipes, water heaters, and appliances; they react with soap to form insoluble scum instead of a proper lather; and they leave visible spotting on glassware and a duller feel in fabric. A water softener fixes all of that — but it doesn't do it for free. The most common softening method, ion exchange, removes calcium and magnesium by trading them for sodium, one ion for another. That's a real chemical tradeoff, not a footnote.