Buy online compatible placement Filters for Viqua Four Stage Reverse Osmosis System / Part# RO-4S Re - Set Of 4 Reverse osmosis filter cartridges for the older model with 10" filters which is 2 vertical filters,  one RO membrane horizontal on top and a final filter, inline carbon. 
Filter as last stage.
 
The different filters represent the different stages that the water goes through while being purified.
 
Generally, Pre - Filters and Post-Filters in RO systems can last around 8 To 12 months between changes.
Only the Organic RO membranes can last as long as 5 years.
 
Stage - 1 
Sediment pre-filter – removes dirt, rust, sediment, sand, and other particulate.
 
Micron rating: 5 Micron.
Dimensions: ( 9 7/8" ) x 2.5"
Lifetime: Replace every year, depending on the water quality.
This filter is wrapped and sealed and meets NSF Standards and Regulations. The filter will fit any residential reverse osmosis unit with standard 10" filter housing.
 
Stage -2 ( carbon block filter)
This unique filter can do the job as a Sediment filter and carbon filter 2-in-1 carbon block filters 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 carbon filters are made with Organic high-quality coconut shell carbon.
 
Micron rating: 5 Micron.
Dimensions: ( 9 7/8" ) x 2.5"
Lifetime: Replace every year, depending on the water quality.
This filter is wrapped and sealed and meets NSF Standards and Regulations. The filter will fit any residential reverse osmosis unit with standard 10" filter housing.
 
Stage - 3
Organic reverse osmosis membrane 50 Gallon per day NSF certified Thin film TFC membrane is the main component of Watershield Reverse osmosis unit. They are made with 100% Organic fine thin film flat sheet.
99% reduction rate of bacteria, pesticides, herbicides, and heavy metals from tap water.
Only the organic membrane has The micron rating of a thin film less than 1/10000th of a Micronwhich is 620,000 Times finer than A human hair, 2,500 Times smaller than bacteria 20 Times smaller than any virus.
 
Product Features:
50 Gallons per day (15.6 Liters per Hour) capacity.
99% Stabilized salt rejection (Minimum Rejection 98%).
NSF/ANSI standard 58 listed Operating Conditions Performance specifications based on 500 ppm.
 
Stage 4 -
inline carbon block is one that easily install directly to your water line and reduces weeping or seepage potential. This filter uses granular activated carbon to reduce chlorine, taste and odor, cysts, and sediment particles up to 1 micron. Available with various fittings to meet your water line's specifications.
 
Micron Rating: 1 micron
Dimensions: 11.25" X 2.125"
Replace every 6-12 months
Reduces chlorine, taste and odor
Reduces cysts