Reverse Osmosis, Checked

Reverse osmosis is the most thorough drinking-water filtration you can put in a home: a semipermeable membrane that strips out dissolved solids most carbon filters can’t touch — lead, arsenic, fluoride, nitrates and PFAS among them. It’s also a category full of inflated claims, confusing specs (gallons per day measured under ideal lab pressure) and running costs most listings never mention. This hub covers RO the way we cover everything: certifications verified, waste-water ratios stated, five-year costs totaled.

We’ll compare tankless under-sink systems against traditional tank systems, countertop units for renters against plumbed-in installs, and explain the numbers that actually matter: recovery rate (how much water goes down the drain per gallon made), flow at real household pressure, filter replacement intervals, and remineralization — because RO removes the good minerals along with the bad, and flat-tasting water is the top reason systems get unplugged.

Every RO system we recommend must carry a verifiable NSF/ANSI 58 listing (or IAPMO equivalent) for the complete system, and we flag any model whose certification covers only the membrane or a single cartridge. If a claim can’t be traced to a listing or a published lab test, we say so — in the review, not in a footnote.

Comparing RO against a simpler carbon filter? The water filters hub lays out both. Want the ownership math before the hardware? Run any two finalists through our 5-year true-cost calculator, and read our methodology is always open at how we check.