Reverse Osmosis systems, RO, use pressure to force water through a semi-permeable membrane. Over 95% of all impurities can be removed. RO systems are one of the most expensive systems to install, but can substantially reduce additional chemical treatment requirements, leading to an acceptable payback.
RO systems are typically used ahead of DI (de-ionization) systems. The DI system can further treat the water for impurities and control pH.