Start with the water entering the home and the condition of the plumbing already in place.
Minerals in water leave deposits as water dries on fixtures and moves through equipment. Aerators, showerheads, appliance connections, and water-heater components often show the buildup first. Heated water makes mineral scale more noticeable, so water-heating equipment can reveal a problem that is less obvious at a cold-water tap.
The condition of the plumbing matters when choosing treatment. Deposits in older pipes and fixtures can affect what shows up at taps, while homes with newer plumbing may show mineral effects most clearly at water-heating equipment. Looking at both the incoming water and the existing plumbing helps separate a water-quality concern from buildup already present in the system.
Filtration and softening do different jobs. A filter may target sediment, taste, odor, or another specific characteristic, while a softener is intended to address hardness minerals. The right setup depends on the concern being addressed and the household demand, not on the assumption that one device handles every water issue.