While every reverse osmosis (RO) system we carry comes with an owner’s manual which states how often to replace the filters and membranes which the systems use to purify the product’s water, we are often asked how frequently these items should be replaced, so I thought this would be a good time to not only answer that question, but to explain the function of each filter.
The RO’s pre-filter is just that, it pre-filters the water coming into the RO system. It is designed to remove and particles in the water of 5 microns or larger, thus protecting the membrane. In at least a couple of the RO systems we carry, a combination carbon/sediment pre-filter is available. A carbon/sediment pre-filter is a good choice for your RO system if your water contains chlorine. Chlorine can damage a typical RO membrane so unless your water comes from your own private well, a carbon/sediment pre-filter is a good choice. Most manufacturer’s recommend changing this filter every 6 months.
Next is the carbon filter. These filters offer a 2nd layer of protection against chlorine but they also reduce other chemicals which can affect RO membrane performance. The manufacturer’s recommend changing these filters every 8 months.
Next is the RO membrane. In the case of the GE Merlin RO, there are actually two of these membranes. A membrane is technically not a filter at all. In the case of a filter, all water passes through it. An RO membrane does not allow anything but pure water to pass. It rejects contaminants and channels them down the drain. An RO membrane should be changed every 2 to 3 years, but if regular pre-filtration changes were neglected, then the membrane should be changed sooner as it is likely damaged.
Finally there is the carbon post-filter. Not all RO’s have a carbon post-filter. They are generally inline between the membrane and the tank/faucet. These post-filters contain activated carbon and remove any ‘plastic taste’ the water might contain after running through the RO system’s lines. This filter should be replaced every year or after any membrane replacement is performed.