When Should I Replace Multipure Water Filter?
Multipure recommends you change them 1 annually, 2 when the system reaches its rated capacity, 3 when the flow rate diminishes, or 4 when the filter becomes saturated with bad tastes and/or odors. To be covered under the lifetime guarantee you need to at least change the Multipure filters annually.
You might take the filter out and the prefilter around the filter is pristine, this does not mean the filter is still filtering properly as that is to collect sediment and if you do not have much the prefilter will look clean. So this is not an indicator that the filter is still absorbing contaminants in the carbon block beneath the prefilter , as the carbon will only absorb so much before it is exhausted.