Reverse osmosis forces water through a very fine membrane to separate most dissolved matter.
The stages
A sediment filter first retains coarse particles such as sand and rust. Carbon filters remove most of the chlorine, which protects the membrane. The membrane separates dissolved matter, the purified water collects in the tank and passes a final carbon filter before the tap.
Why replacement is needed
Filters fill up over time. The interval depends on water quality, which is why regular maintenance matters.