The first three stages are for pre-filtration.
Pre-filtration removes impurities such as dust and chlorine that can clog the RO membrane or damage it.
By pre-filtering some of the impurities, the membrane is left to deal with the hardest-to-remove contaminants, which improves overall performance.
The first pre-filter is a sediment filter.
It removes large impurities suspended in water, including dust, rust, and silt. The filter is designed to hold large amounts of dirt and resist damage from a wide range of chemicals.
The filter housing is transparent so you can see how much dirt has been filtered from the water. This helps you determine when it’s time to replace the filters.
Next up is a GAC or granular activated carbon filter.
It removes chlorine and various other chemicals that affect the taste and smell of water. It also filters out any fine sediment that has passed through the sediment filter.
Water then goes through a carbon CTO filter. This one can remove smaller impurities that escaped the GAC filter.
It tackles tougher chemicals like chloramines, certain pesticides, hormones, pharmaceuticals, and other organic chemicals.
By now, most of the impurities remaining in the water are dissolved salts and other inorganic compounds like chromium and arsenic.
Most of the biologicals – bacteria, viruses, and cysts –also remain untouched, for now.