iSpring is a useful brand to compare when you want multiple filtration paths within one lineup, from point-of-use reverse osmosis to broader whole-house filtration. The best fit depends on the exact model, your water-quality goals, available installation space, flow needs and ongoing filter costs.

Before buying: compare filtration technology, certification for the exact model, gallons-per-day capacity, wastewater efficiency, replacement-filter schedule and cost, installation needs, remineralization options and the space available under your sink or on your countertop.