The 4 Stage System is perfect for home use and one of the most popular systems we offer. Stage 1 is Sediment 1 Micron which removes physical particles such as dirt sediment and sand. Stage 2 is the Carbon Block with reduces the presence of chemicals such as chlorine which may be present in the water supply. Stage 3 is the Reverse Osmosis Membrane. Stage 4 is Alkaline which involves a re-mineraliser containing crushed marble and/or crushed limestone.