Interested in buying reverse osmosis filter replacements?Then 4 Stage Reverse Osmosis Replacement Filters is the perfect choice for you. Our 4 stage reverse osmosis system is made up of a sediment pre-filter, a carbon block pre-filter, a reverse osmosis membrane, and a carbon block post-filter. We recommend replacing the RO Membrane and Post Filter once every 2 to 3 years. Easy to replace and install. Buy this amazing product.