In terms of absolute performance, reverse osmosis water filters are the best you can get. In addition to a carbon filter that neutralizes chlorine and many industrial chemicals — just as you find in most pitcher-type filters — they employ a finely porous membrane that physically prevents dissolved metals, forever chemicals, and almost anything else but water from passing through. As a result, they produce virtually pure water. It’s so pure, in fact, that many RO filters add minerals back to it, just so it tastes nice.I tested examples of the three main varieties of reverse osmosis filters: a traditional tank-equipped under-sink model, the Cloud RO; two tankless under-sink filters, Delta’s Clarifi and the Waterdrop X12; and a pump-equipped countertop filter, the AquaTru Classic.All of them have the NSF/ANSI certifications that we require of water filters. And each model has distinct advantages. But after our hands-on testing, the traditional, tank-equipped Cloud RO won out for its simplicity, reliability, and convenience, and it’s our top pick.