It is advised that Reverse Osmosis (RO) membranes be replaced every 2-3 years or based on actual usage, consumption and water quality. In high TDS areas, the RO membrane may need replacement more frequently. The specification of the RO membrane must be matched as per the quality of water. For example, if the capacity of the RO membrane is to purify up to 1000 ppm of TDS, passing water higher in TDS than the recommended level will reduce membrane life.
As we know the heart of every reverse osmosis unit is the membrane – the reverse osmosis membrane is typically made from a thin-film composite (TFC), semi-permeable material which can be degraded by chlorine. Thus chlorine must be removed from the water using a carbon filter, and as we know it is also recommended to use a sediment pre-filter cartridge filter to protect the carbon filter. The sediment and carbon filter don’t really reduce TDS, on the other hand they protect the membrane from undissolved solids and chlorine in the water:
Changing sediment and carbon filters is preventive maintenance to avoid trashing the RO membrane and is unrelated to the TDS. These three filter components complete the three stages required for all reverse osmosis systems:
Stage 1 : Sediment filter : It removes undissolved solids from water to prevent the carbon stage from getting blocked with sediment rapidly.
Stage 2 : Carbon filter : It removes chemicals from water which can damage the RO membrane, particularly chlorine in tap water. The carbon filter will also act as a sediment filter but once its pores become blocked with sediment, its ability to remove chlorine from the water is reduced.
Stage 3 : RO membrane : The job of the membrane is to remove the bulk of the dissolved solids from the water, typically over 95% of TDS is removed by the membrane.
Different water sources have different levels of sediments in the water and the levels of these sediments can change. It is also impossible to give a fixed time but 6 months should be the maximum interval for replacing sediment and carbon filters. You may need to replace them more often if making a lot of water or if you have very high sediment in the source water. For optimum efficiency of RO membrane, routine maintenance should be performed on Reverse Osmosis systems.