There are different types of filtration systems, and the reverse osmosis system is definitely one of the best in the market today. Its effectiveness largely depends on a lot of factors such as the type of membrane, the water pressure and concentration of contaminants. RO system uses pressure which forces the external supply of water to flow through the membrane and passes out of the faucet after undergoing the different stages of filtration. All the impurities that were blocked from passing through the semi-membrane are usually discarded and wasted away to drain. Read more: http://www.reverseosmosisguides.com/how-does-reverse-osmosis-system-work/