When the source water enters the system it goes through stages one, two, and three, collectively known as the pre-filters. The job of the pre-filters is to remove large contaminants and protect the RO membrane from chemicals like chlorine and chloramines.
After the water has passed through the pre-filters, it is forced through the reverse osmosis (RO) membrane, the same technology used to produce bottled water. This semi-permeable membrane features tiny 0.0001 micron sized holes, equivalent to just 0.000000004 of an inch. This allows it to effectively remove a long list of water contaminants only possible with reverse osmosis.
The fifth and final stage of filtration utilizes a finer GAC filter known as the post carbon filter. This provides a final polishing before the purified water is delivered to the faucet.
The end result is bottled quality water. In addition to the cost savings and health benefits, widespread use of in home filtration systems would reduce the impact of plastic bottles on the environment tremendously. With all of the benefits, it only makes sense to go RO.