Water filtering by reverse osmosis is efficient on its own due to its ability to remove almost all kinds of particles from incoming tap water. High pressure moves water through a semi-permeable membrane and this water undergoes ion exclusion (the process where bacteria (other contaminates) and water are separated). The membrane removes the contaminants and are flushed down the drain. There are two different types of membranes, each with its own special quality of efficiency in the water filtration system:
Cellulose Triacetate Membrane (CTA) – this membrane is made up of paper by-product membrane bonded to a synthetic layer. It has higher contaminant removal than cellulose acetate. In fact, CTA is tolerant of chlorine water but has lower contaminant removal than TFC.
Thin Film Composite Membrane (TFC) – This membrane has a thin film dense layer and a porous support layer linked together. TFC is more expensive as it can only filter chlorine-free water, which is the reason why a carbon filter is installed ahead of the membrane; that is, water is made to undergo carbon filtration first. The TFC membrane has higher water flux and salt rejection than CTA membranes. This membrane is good for filtering brackish water (water that has more salt than fresh water but less salt than seawater). The TFC membrane is best for purifying drinking water.
Whichever membrane is suitable depends on the nitrate level of tap water. If there’s a higher nitrate level in the water, the TFC membrane is the best choice. If not, use the CTA membrane. The CTA membrane is replaced more often than the TFC membrane, which can last for two to three years before replacement.