R/O was originally developed in the 1950’s and has been considered the ultimate water filtration technology. A semi-permeable membrane essentially passes some atoms or molecules but not others. Tap water is put on one side of the membrane and pressure is applied to pass water, but not dissolved solids through the membrane and on to drinking. It generally takes a lot of pressure and is fairly slow, but it works.

The biggest challenges to R/O systems have been:

Time: Traditional R/O systems are very slow to produce water
Waste: R/O typically wastes of 75% of treated water
Chlorine Oxidation: Exposure to chlorine escaping from poor quality carbon pre-filters can significantly shortens