Reverse osmosis (RO)

Reverse osmosis

A point-of-use filter that pushes water through a fine membrane, pulling out dissolved contaminants that carbon filters miss.

Installed under the kitchen sink, reverse osmosis forces water under pressure through a semi-permeable membrane, and it is the one filter type that reliably handles the full range of drinking-water concerns: it removes the large majority of both long- and short-chain PFAS, along with lead, hexavalent chromium, nitrate, and perchlorate, the soluble compounds an ordinary carbon filter leaves in the water. Two tradeoffs come with that reach. RO sends a portion of each batch down the drain as reject water, so it uses more water per glass produced than a carbon filter. It also strips out the beneficial minerals, like calcium and magnesium, that carbon filtration leaves intact. RO works at the tap, treating the drinking-water route only. It does nothing about PFAS or other exposures that arrive through food, packaging, or household dust.