5 STAGE PA-E under sink reverse osmosis water systems include 3 pre-filters and a membrane that must be replaced periodically. 
The different filters represent the different stages  that the water goes through while being purified.Generally Pre-Filters and Post-Filters in the PA-E RO 132 water systems can last aroumd 8 To 12 months between changes. RO membranes can last as long as 2 to 3  years . 
 
        Stage 1 - Pre-Membrane reverse osmosis sediment filters
Replacment High-Grade 5 micron high-capacity  sediment filter 
Remove larger particles & suspended matter such as dirt, silt, rust, sand from water.   
Protects and extends the life of the membrane and system.
Recommend replace every 8 -12 months, varies depend on the water source quality   
Standard Size  water filters 24-3/4" / 10" 5.5 /15-( 97%)
Stage (1) Pre-Membrane
 
            Stage 2- Organic Activated Carbon GAC filter 
Are well-known for their highly efficient reduction of chlorine taste and odor taste and odors of many organic chemicals and volatile organic compounds.
All GAC filters are made with Organic high quality coconut shell carbon. Micron rating: 5 Micron.
Dimensions: ( 9 3/4 ) x 2.5"
Lifetime: Replace every year, depending on the water quality.
This filter is wrapped and sealed and meets NSF Standards and Regulations. Filter will fit any Residential Reverse Osmosis Unit that features standard 10” filter housing  
    
          Stage 3- CTO Coconut Shell Carbon Block Filter 
Organic CTO Coconut Shell Carbon Block Filter
Forceful remove pesticide residues in water, water pollution odor of ozone, chlorine removal of residual heavy metals, bacteria, sterilization rate if 99%.
Standard Size 9 3/4" / 10" 5.5 /15-( 97%)pxi - CVM
Recommend replace every 8 To 12 months.
Protects and extends the life of the membrane and system.