Reverse Osmosis Process (RO) is a modern day advancement in water purification. The core of the process is a reverse osmosis membrane with tiny pores. When water gets pressured through it, membrane produces two outputs: clean water that's pure enough to have very few contaminants left, and a "dirty" output that in drinking water applications is typically discarded down the drain. Since pressure was used , and membrane pores are tiny to let only very small size molecules (like H2O) through, any impurities that are larger molecules will be rejected by it. 

Fits many standard RO systems