Reverse osmosis (RO) systems force water, under pressure, into a module that contains a semipermeable membrane and a number of other filtration steps. A typical RO system has a prefilter designed to capture larger particles, chlorine, and other substances; a semipermeable membrane that captures more contaminants; an activated carbon filter that removes residual taste, odor, and some organic contaminants; and a storage tank to hold the treated water for use.
Whole-house (point-of-entry) RO systems exist, but they are more commonly installed near the point-of-use, such as on a countertop or under a sink. They’re great for treating water for cooking and drinking, but they don’t usually produce large amounts of treated water — more like 3 to 10 gallons a day. For that reason, typically people choose to install RO-treated faucets in the most popular areas of the home such as kitchens and bathrooms, as opposed to installing it for every drinking tap.
Just like any other kind of filter technology, RO systems require regular maintenance. That includes periodically replacing the unit’s prefilters, postfilters, and membrane modules.
Find reverse osmosis systems that are certified to NSF/ANSI 58 and WQA S-300.