01Start with the concern, not the equipment
For an aesthetic concern such as taste or odor, identify whether it occurs at every tap, only on hot water or only after water sits. For a safety concern, use a certified laboratory and choose a device certified for the contaminant.
02Common filter locations
Whole-house systems treat water near the point of entry. Under-sink systems treat one drinking-water tap. The right location depends on whether the concern affects bathing, appliances, all fixtures or only drinking and cooking.
03Filters need a maintenance plan
Every filter has a finite capacity. Replacement intervals depend on water quality and consumption, not just calendar time. Pressure drop, bypass design and replacement cost belong in the buying decision.